Teledyne TV Video Accessories HPM 2002 OBE User Manual

TELEDYNE  
HASTINGS  
INSTRUMENTS  
INSTRUCTION MANUAL  
HPM-2002-OBE  
VACUUM GAUGE  
I S O 9 0 0 1  
C E R T I F I E D  
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Table of Contents  
1. GENERAL INFORMATION............................................................................................................................................ 5  
1.1.  
1.2.  
1.3.  
1.4.  
1.5.  
1.6.  
1.7.  
FEATURES:............................................................................................................................................................. 5  
MODEL 2002 SENSORS........................................................................................................................................... 5  
HPM-2002-OBE ANALOG OUTPUT MODULE........................................................................................................ 5  
HPM-2002-OBE ANALOG OUTPUT (4-20MA) MODULE ....................................................................................... 5  
HPM-2002-OBE RS232/485 OUTPUT MODULE.................................................................................................... 6  
HPM-2002-OBE DEVICENET MODULE................................................................................................................. 6  
SPECIFICATIONS..................................................................................................................................................... 6  
2.  
3.  
INSTALLATION.......................................................................................................................................................... 7  
2.1.  
RECEIVING INSPECTION ......................................................................................................................................... 7  
QUICK START......................................................................................................................................................... 7  
TRANSDUCER INSTALLATION................................................................................................................................. 7  
OBE MODULE INSTALLATION ............................................................................................................................... 7  
INITIAL OPERATION ............................................................................................................................................... 8  
2.2.  
2.3.  
2.4.  
2.5.  
OPERATING INFORMATION.................................................................................................................................. 9  
3.1.  
ANALOG OUTPUT (0-10V) ..................................................................................................................................... 9  
3.1.1. Overall Functional Description........................................................................................................................ 9  
3.1.2. High and Low Set Point Modes ........................................................................................................................ 9  
3.1.3. Run Mode ....................................................................................................................................................... 10  
3.1.4. Cal Mode........................................................................................................................................................ 10  
3.1.5. GAS Mode....................................................................................................................................................... 11  
3.1.6. Analog Output (0-10V)................................................................................................................................... 11  
3.2.  
ANALOG OUTPUT (4-20MA) ................................................................................................................................ 13  
3.2.1. Overall Functional Description...................................................................................................................... 13  
3.2.2. High and Low Set Point Modes ...................................................................................................................... 13  
3.2.3. Run Mode ....................................................................................................................................................... 13  
3.2.4. Cal Mode........................................................................................................................................................ 14  
3.2.5. GAS Mode....................................................................................................................................................... 15  
3.2.6. Analog Output (4-20mA) ................................................................................................................................ 15  
3.3.  
RS232/485 WITH DISPLAY .................................................................................................................................. 17  
3.3.1. Overall Functional Description...................................................................................................................... 17  
3.3.2. COMMAND SYNTAX..................................................................................................................................... 17  
3.3.3. Interrogation Commands................................................................................................................................ 18  
3.3.4. Paramater Modification Commands .............................................................................................................. 18  
3.3.5. Calibration Adjustment Commands................................................................................................................ 19  
3.3.6. Reset / Restore Commands ............................................................................................................................. 19  
3.3.7. Device Status .................................................................................................................................................. 20  
3.3.8. Default RS232/485 Specifications .................................................................................................................. 20  
3.3.9. Modular Connector Pinout (R2-232) RJ-11 connector on left side................................................................ 21  
3.3.10.  
3.3.11.  
3.3.12.  
3.3.13.  
Modular Connector Pinout (RS-485)......................................................................................................... 21  
High and Low Set Point Modes ................................................................................................................. 21  
Run Mode................................................................................................................................................... 22  
Cal Mode ................................................................................................................................................... 22  
3.4.  
DEVICENET TM ..................................................................................................................................................... 23  
3.4.1. Overall Functional Description...................................................................................................................... 23  
3.4.2. DeviceNet description .................................................................................................................................... 23  
3.5.  
CALIBRATION OF THE HPM-2002-OBE............................................................................................................... 24  
3.5.1. Zero Coefficient Adjustment........................................................................................................................... 24  
3.5.2. Midrange Coefficient Adjustment................................................................................................................... 24  
3.5.3. Atmosphere Coefficient Adjustment................................................................................................................ 24  
4.  
THEORY OF OPERATION ..................................................................................................................................... 25  
4.1.1. ............................................................................................................................................................................. 25  
4.2.  
4.3.  
PIEZORESISTIVE SENSOR...................................................................................................................................... 26  
PIRANI SENSOR .................................................................................................................................................... 28  
HPM-2002-OBEVacuum Gauge  
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4.4.  
DUAL SENSOR OPERATION .................................................................................................................................. 30  
5.  
6.  
7.  
TROUBLESHOOTING ............................................................................................................................................. 32  
5.1.  
5.2.  
ADVANCED SETUP GUIDE .................................................................................................................................... 32  
FREQUENTLY ASKED QUESTIONS ........................................................................................................................ 34  
WARRANTY .............................................................................................................................................................. 36  
6.1.  
6.2.  
WARRANTY REPAIR POLICY ................................................................................................................................ 36  
NON-WARRANTY REPAIR POLICY ....................................................................................................................... 36  
DIAGRAMS AND DRAWINGS ............................................................................................................................... 37  
HPM-2002-OBEVacuum Gauge  
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1. General Information  
The Hastings HPM-2002-OBE is a small, low cost electronics module which provides the user with  
accurate vacuum measurements over a wide range of pressure. The HPM-2002-OBE uses the same rugged  
HPM-2002s transducer tube as the HPM-2002 bench top instrument. This tube features two sensors; a  
patented thin-film Pirani sensor and a piezoresistive sensor combined in a single tube with a matched EEPROM  
(Electrically Erasable/Programmable Read Only Memory).  
The HPM-2002-OBE electronics module combined with the HPM-2002’s tube provides accurate vacuum  
measurement from 1x10-4 Torr to 1000 Torr. The HPM-2002-OBE is designed for quick, easy installation and  
will provide the user with long lasting, trouble free, reliable vacuum measurement.  
1.1. Features:  
Low-Cost Electronics Module  
Wide Dynamic Range 1x10-4 Torr to 1000 Torr  
Combined Sensors in a Single Tube  
Input Voltage (11.5-30 VDC)  
Connector: 15-pin high-density male “D”  
Optional 4-digit LED Display  
Optional Outputs (Dual 0-10 volt analog or RS232/485)  
1.2. Model 2002 Sensors  
The Model 2002 transducer tube is comprised of an ion implanted piezoresistive, direct force sensor and a  
thin film Pirani type sensor. The Pirani sensing element is a Pt thin film serpentine element deposited on a 1  
micron thick Si3N4 membrane. The membrane is peripherally supported by a Si box shaped die and is covered  
by a thick Si lid parallel to the membrane and open on two ends. The piezoresistive unit is an ion implanted  
Wheatstone bridge in a 50 micron thick Si membrane peripherally supported by a Si box shaped die which has  
been anodically bonded to a Pyrex substrate.  
The dual sensor assembly is encased in a corrosion resistant 316 stainless steel tube shell. The durable tube  
design withstands high pressure (150 psig/10.2 bar) and high pressure surges. Since the Pirani sensor is  
miniaturized and employs a Pt thin film on a Si3N4 membrane (instead of a conventional long fragile wire), the  
transducer can withstand high levels of mechanical shock.  
The Model 2002 is designed for fast response. The micro machined sensing elements have a very small  
mass and operate in a constant temperature (Pirani) and a constant current (piezo) feedback mode. This makes  
response time very fast as compared to other commercially available sensors which have to change the  
temperature of a significant mass to reflect pressure changes and have a large internal volume which must  
equalize in pressure with the system before the sensor can reach its final value. The transducer’s small internal  
volume (<1.5 cc) permits rapid pneumatic response to system pressure changes. Further, the small geometry of  
the transducer prevents thermal convection currents which allows the sensor to be mounted in any orientation  
without calibration shifts.  
1.3. HPM-2002-OBE Analog Output Module  
The analog output (0-10 V) module consists of a power conversion/sensor transducer board,  
microprocessor board and a user interface option board. Two 0-10 Volt linear outputs are generated for the user  
via the high-density 15-pin “D” connector. The first of these outputs covers the pressure range from 0 to 1024  
Torr. The second output covers the range from 0 to 1000 mTorr. A four digit floating-point LED display is  
standard.  
1.4. HPM-2002-OBE Analog Output (4-20mA) Module  
(Identical to 1.3, except replace 0-10 V with 4-20 mA)  
HPM-2002-OBEVacuum Gauge  
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1.5. HPM-2002-OBE RS232/485 Output Module  
The RS232/485 module consists of a power conversion/sensor transducer board, microprocessor board and  
a user interface option board. Serial communication is conducted via an RJ-11 type connector. With RS232  
option (EIA-232 Rev. E) communication can easily be established between the module and the serial port of a  
PC. The RS485 option allows the user to address multiple units and allows operation at distances of up to 4000  
feet. The RS232/485 module includes a four digit floating-point LED display.  
1.6. HPM-2002-OBE DeviceNet Module  
The DeviceNet module consists of a power conversion/sensor transducer board, microprocessor board and  
a user interface option board. All communication is conducted via a 5-pin “Micro” style with center pin, male  
pin contacts. The module has passed the ODVA DeviceNet test and conforms to the vacuum/pressure gauge  
device profile, an Electronic Data Sheet (EDS) with limited features is also available upon request.  
1.7. Specifications  
Measuring range ............................................................................................................. 1x10-4 to 10+3 Torr  
..............................................................................................................................1.3x10-4 to 1.3x10+3 mbar  
Accuracy (N2, T=23°C) .................................................................. + 20% of reading (1 x10-3 to 50 Torr)  
............................................................................................................ + 1.5% of reading (50 to 1000 Torr)  
Ambient temperature operating range...........................................................................................0° to 50°C  
Process control .........................................................2 TTL outputs (1 TTL remote zero command input)  
Digital readout.......................................................................................................................Four digit LED  
Equipment operating ranges .......................................................................................................12-30 VDC  
Transducer mounting ............................................................................ Any position without recalibration.  
Transducer internal volume ..............................................................................................................< 1.5 cc  
Wetted material ...................................................................................................... Au, Si3N4, Si, PyrexTM  
,
....................................................................................................................KovarTM, 316 stainless steel and  
....................................................................................................High Temp/Low Outgassing UHV Epoxy  
Weight (OBE & HPM-2002s tube) ..........................................................................12 oz (1/8” NPT tube)  
Calibrated for nitrogen .....................................................Conversion Factors for other gases are selectable  
Burst Pressure (Tube)...................................................................................................................... 150 psig  
Proof Pressure (*) .............................................................................................................................. 30 psig  
Nominal Operating Pressure (Tube) .............................................................................. 1x10-4 to 10+3 Torr  
Input Operating Range ........................................................................................................11.5 to 30 VDC  
Input Power....................................................................................................................24 VDC @ 125 mA  
* Maximum pressure above which may cause permanent damage.  
HPM-2002-OBEVacuum Gauge  
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2. Installation  
This section is designed to assist in getting a new pressure gauge into operation as quickly and easily as  
possible. Please read the following instructions thoroughly before installing the instrument.  
2.1. Receiving Inspection  
Carefully unpack the Hastings Model HPM-2002-OBE Instrument (part # HPM-2002-OBE), and  
transducer tube (part #HPM 2002s-xx). Inspect all items for any obvious signs of damage due to shipment.  
Immediately advise the carrier who delivered the shipment if any damage is suspected.  
Compare each component shipped against the packing list. Ensure that all parts are present (i.e. transducer,  
electronics module, hardware, etc.). Optional equipment or accessories will be listed separately on the packing  
list.  
2.2. Quick Start  
Unpack and inspect all items for any obvious signs of damage due to shipment. Immediately advise the  
carrier who delivered the shipment if any damage is suspected.  
Wire the 15-pin “D” connector according to cable pinout (see Table below) using 24 AWG or other  
suitable wire.  
Using a unipolar DC Power Supply, set the desired operating voltage within the range of 12 VDC to  
30 VDC.  
Connect the HPM-2002-OBE module to the HPM-2002s transducer tube.  
Note that the connector is keyed.  
A finger tight connection is all that is required for adequate operation.  
Transducer tube may be installed in any orientation. However, if condensation is likely to occur, then  
the tube port should be orientated downward.  
When installing 1/8” NPT style transducer tube, use the 7/16” wrench flats.  
Attach cable.  
With the vacuum chamber at atmosphere, turn on the power supply (typically +24 VDC. Gauge is  
now reading pressure.  
For best accuracy, the gauge should now be zeroed. Pump the vacuum system down to low (10-6 Torr)  
pressure if possible. Ideally the gauge should be operated in this condition for one hour before setting  
the “Zero”.  
To set the “Zero”, place the HPM-2002-OBE in the “CAL” mode by using the “SELECT” button.  
Using a small flat head screwdriver, rotate the “ADJUST” rotary encoder until the unit flashes  
between “0.0” and “-0.0”.  
Return to the “RUN” mode by using the “SELECT” button  
2.3. Transducer Installation  
The transducer tube may be installed in any orientation. Although the transducer tube is rugged and will  
perform well in many harsh environments, the tube should be installed in a clean and careful manner. The tube  
is configured with the vacuum fitting requested. If your vacuum environment is highly contaminated or has  
unique fitting requirements, a Hastings filter or special adapter may be needed. Please contact the Hastings  
Instruments Sales Department for assistance in your system configuration.  
2.4. OBE Module Installation  
Environment:  
Indoor use  
Altitude up to 2000 meters  
Operating temperature range from 5 to 40°C  
HPM-2002-OBEVacuum Gauge  
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Maximum relative humidity: 80% for temperatures up to 31°C decreasing linearly to 50% relative  
humidity at 40°C.  
Installation category II  
HPM-2002-OBE  
CABLE PINOUT  
Analog Ouput  
Analog Ouput  
Digital Output  
Pin  
No.  
0-10 Volt  
4-20 mA  
RS232/485  
1
2
High Setpoint Output  
Low Setpoint Output  
High Setpoint Output  
Low Setpoint Output  
High Setpoint Output  
Low Setpoint Output  
3
Power Input (+12 to 30 VDC) Power Input (+12 to 30 VDC) Power Input (+12 to 30 VDC)  
4
5
6
7
8
9
10  
11  
12  
13  
14  
15  
Power Return  
Channel 1 Vout (+)  
Analog Return  
Channel 2 Vout (+)  
Digital Ground  
Remote Zero  
NC  
Power Return  
Channel 1 Iout (-)  
Analog Shield  
Channel 2 Iout (-)  
Digital Ground  
Remote Zero  
Channel 1 Iout (+)  
Channel 2 Iout (+)  
NC  
Power Return  
NC  
NC  
NC  
Digital Ground  
Remote Zero  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
NC  
Rx In (Internal Use)  
Tx Out (Internal Use)  
Rx In (Internal Use)  
Tx Out (Internal Use)  
2.5. Initial Operation  
Upon applying power to the control unit a pressure measurement will be given in Torr for nitrogen.  
However, it is recommended that the user follow the instructions for zeroing and adjusting the output at  
atmosphere.  
HPM-2002-OBEVacuum Gauge  
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3. Operating Information  
This section contains information on operating the HPM-2002-OBE in any of its various configurations.  
Refer to the appropriate section for information on the mode in use.  
3.1. Analog Output (0-10V)  
3.1.1.  
Overall Functional Description  
The status bar gives information about the condition of the HPM-2002-OBE. High and Low indicate  
whether the set points are activated. ERROR indicates if there was a problem downloading the EEPROM. Torr  
and mTorr indicate what pressure regime the gauge is measuring.  
The mode bar indicates which mode has been selected. The HPM-2002-OBE has five modes which the  
user may enter. This is similar to the six modes which can be entered in the bench top/panel mounted HPM-  
2002, there is no interlock feature; when the user changes the setting within a mode, any adjustments that have  
been made will be permanent once the mode is exited. To exit without making changes permanent, the user  
must turn the power off.  
3.1.2.  
High and Low Set Point Modes  
The HPM-2002-OBE provides TTL outputs for process control. These signals are available on the 15-pin  
connector (see previous table in Section 2.4).  
To view the High set point, place the HPM-2002-OBE in the High mode by pressing the SELECT button  
until the High mode light is illuminated. The display then shows the set point selected. During normal operation  
the alarm light will illuminate and the TTL output (pin # 1) will go high (+5V) if the pressure exceeds the set  
point.  
Similarly, to view the Low set point, place the HPM-2002-OBE in the Low mode by pressing the SELECT  
button until the Low mode light is illuminated. The display then shows the set point selected. During normal  
operation the alarm light will illuminate and the TTL output (pin # 2) will go high (+5V) if the pressure  
becomes less than the set point.  
To adjust a setpoint, place the HPM-2002-OBE in either setpoint mode (High or Low). Next, use the  
ADJUST rotary encoder until the desired setpoint is displayed. Finally, place the HPM-2002-OBE back in the  
Run mode. The new setpoints are now stored in the HPM-2002-OBE’s memory.  
HPM-2002-OBEVacuum Gauge  
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3.1.3.  
Run Mode  
The HPM-2002-OBE will automatically enter the Run mode upon start-up. This is the mode for normal  
operation and the mode in which the instrument will spend most of its time. In the Run mode the HPM-2002-  
OBE will continuously monitor the pressure, update the alarm conditions, and update the display about ten  
times a second.  
3.1.4.  
Cal Mode  
Optimal performance of the HPM-2002-OBE is achieved by performing in situ adjustments to the  
calibration coefficients in the Cal mode. There are three calibration coefficients. These are the zero coefficient,  
the midrange coefficient, and the atmosphere coefficient. Once a tube has been fully calibrated the midrange  
coefficient should never need further adjustment, but it may be helpful to adjust the zero coefficient or the  
atmosphere coefficient under certain circumstances. The CAL MODE presupposes that the operator is  
applying a known pressure of the correct gas composition (see GAS MODE). The factory calibration points are  
800 Torr, 7 Torr, and < 10-6 Torr. The user’s calibration points are not required to be exactly those values, but  
should be somewhat close, and must be within the ranges shown in the following figure. The HPM-2002-OBE  
detects the voltage signal within the sensor tube, which is converted and displayed as a pressure reading. The  
resulting pressure reading determines which of the three coefficients will be adjusted.  
The operator action is the same for adjustment of all three of the coefficients, except that he must apply the  
proper calibration pressures according to the calibration point he is about to adjust. To adjust a calibration  
HPM-2002-OBEVacuum Gauge  
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coefficient, place the HPM-2002-OBE in the Cal mode using the SELECT button. Then turn the ADJUST  
rotary encoder. The Cal light will begin to flash during adjustment and will continue to flash until the Cal mode  
is exited using the SELECT button.  
To perform a full calibration on the HPM-2002-OBE, first use the Zero Coefficient Adjustment Procedure.  
Followed by the Midrange Coefficient Adjustment Procedure, and finally perform the Atmosphere Coefficient  
Adjustment Procedure. Sensor Coefficients are stored in the Sensor’s EEPROM upon exiting the Cal mode.  
3.1.5.  
GAS Mode  
The HPM-2002-OBE can provide true pressure measurements in many gas environments. At pressure  
levels where the direct force piezoresistive sensor is operative, the instrument is gas composition independent  
and measures the true pressure regardless of gas composition. The Pirani is gas composition sensitive so the  
actual composition must be known and the Pirani calibrated in that gas. When the vacuum system’s gas  
composition is dominated by a single gas species (for example, during system venting with an inert gas), the user  
can enter a gas selection into the HPM-2002-OBE by rotating the ADJUST rotary encoder. To view the gas  
selection, depress the SELECT button until the GAS light is illuminated. The number on the display  
corresponds to the gas. See the table below.  
Gas Selection Table  
Gas Mode  
Gas  
Displayed Number  
00  
01  
02  
03  
04  
Nitrogen  
Argon  
Helium  
Water Vapor  
Custom  
3.1.6.  
Analog Output (0-10V)  
The dual (0 - 10V) output option board provides voltage outputs proportional to the HPM-2002-OBE’s  
pressure reading. The first channel (pin 5) corresponds to the higher-pressure range (0 - 1024 Torr). The  
second channel (pin 7) corresponds to the lower pressure range (0 - 1000 mTorr). The equation below gives the  
output voltage on the pressure:  
pressure  
V (channel1) =  
100  
V (channel2) = 10× pressure  
Where V(channel 1) is the voltage between pins 5 and 6, V(channel 2) is the voltage between pins 7 and 6,  
and the pressure is indicated in Torr.  
HPM-2002-OBEVacuum Gauge  
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3.2. Analog Output (4-20mA)  
The HPM-2002-OBE with analog output and display is shown in the figure below. The user interface  
consists of a status bar, a mode bar, and setpoint test jacks.  
3.2.1.  
Overall Functional Description  
The status bar gives information about the condition of the HPM-2002-OBE. High and Low indicate  
whether the set points are activated. Error indicates if there was a problem downloading the EEPROM. Torr  
and mTorr indicate what pressure regime the gauge is measuring.  
The mode bar indicates which mode has been selected. The HPM-2002-OBE has five modes which the  
user may enter. This is similar to the six modes which can be entered in the bench top/panel mounted HPM-  
2002, there is no interlock feature; when the user changes the settings within a mode any adjustments that have  
been made will be permanent once the mode is exited. (To exit without making changes permanent, the user  
must turn the power off.)  
3.2.2.  
High and Low Set Point Modes  
The HPM-2002-OBE provides TTL outputs for process control. These signals are available on the 15-pin  
connector (see previous table in Section 2.4).  
To view the High set point, place the HPM-2002-OBE in the High mode by pressing the SELECT button  
until the High mode light is illuminated. The display then shows the set point selected. During normal operation  
the alarm light will illuminate and the TTL output (pin # 1) will go high (+5V) if the pressure exceeds the set  
point.  
Similarly, to view the Low set point, place the HPM-2002-OBE in the Low mode by pressing the SELECT  
button until the Low mode light is illuminated. The display then shows the set point selected. During normal  
operation the alarm light will illuminate and the TTL output (pin # 2) will go high (+5V) if the pressure  
becomes less than the set point.  
To adjust a setpoint, place the HPM-2002-OBE in either setpoint mode (High or Low). Next, use the  
ADJUST rotary encoder until the desired setpoint is displayed. Finally, place the HPM-2002-OBE back in the  
Run mode. The new set points are now stored in the HPM-2002-OBE’s memory.  
3.2.3.  
Run Mode  
The HPM-2002-OBE will automatically enter the Run mode upon start-up. This is the mode for normal  
operation and the mode in which the instrument will spend most of its time. In the Run mode the HPM-2002-  
HPM-2002-OBEVacuum Gauge  
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OBE will continuously monitor the pressure, update the alarm conditions, and update both analog output  
channels about ten times a second.  
3.2.4.  
Cal Mode  
Optimal performance of the HPM-2002-OBE is achieved by performing in situ adjustments to the  
calibration coefficients in the Cal mode. There are three calibration coefficients. These are the zero coefficient,  
the midrange coefficient, and the atmosphere coefficient. Once a tube has been fully calibrated the midrange  
coefficient should never need further adjustment, but it may be helpful to adjust the zero coefficient or the  
atmosphere coefficient under certain circumstances.  
The CAL MODE presupposes that the operator is applying a known pressure of the correct gas  
composition (see GAS MODE). The factory calibration points are 800 Torr, 7 Torr, and < 10-6 Torr. The  
user’s calibration points are not required to be exactly those values, but should be somewhat close, and must be  
within the ranges shown in the following figure. The HPM-2002-OBE detects the voltage signal within the  
sensor tube, which is converted and displayed as a pressure reading. The resulting pressure reading determines  
which of the three coefficients will be adjusted  
The operator action is the same for adjustment of all three of the coefficients, except that he must apply the  
proper calibration pressures according to the calibration point he is about to adjust. To adjust a calibration  
coefficient, place the HPM-2002-OBE in the Cal mode using the SELECT button. Then turn the ADJUST  
rotary encoder. The Cal light will begin to flash during adjustment and will continue to flash until the Cal mode  
is exited using the SELECT button.  
HPM-2002-OBEVacuum Gauge  
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To perform a full calibration on the HPM-2002-OBE, first use the Zero Coefficient Adjustment Procedure.  
Followed by the Midrange Coefficient Adjustment Procedure, and finally perform the Atmosphere Coefficient  
Adjustment Procedure. Sensor Coefficients are stored in the Sensor’s EEPROM upon exiting the Cal mode.  
3.2.5.  
GAS Mode  
The HPM-2002-OBE can provide true pressure measurements in many gas environments. At pressure  
levels where the direct force piezoresistive sensor is operative, the instrument is gas composition independent  
and measures the true pressure regardless of gas composition. The Pirani is gas composition sensitive so the  
actual composition must be known and the Pirani calibrated in that gas. When the vacuum system’s gas  
composition is dominated by a single gas species (for example, during system venting with an inert gas), the user  
can enter a gas selection into the HPM-2002-OBE by rotating the ADJUST rotary encoder. To view the gas  
selection, depress the SELECT button until the GAS light is illuminated. The number on the display  
corresponds to the gas. See the table below.  
Gas Selection Table  
Gas Mode  
Gas  
Displayed Number  
00  
01  
02  
03  
04  
Nitrogen  
Argon  
Helium  
Water Vapor  
Custom  
3.2.6.  
Analog Output (4-20mA)  
The dual output option board provides current output proportional to the HPM-2002-OBE’s pressure  
reading. The first channel (pins 5 & 10) corresponds to the higher-pressure range (1-1024 Torr). The second  
channel (pins 7 & 11) corresponds to the lower pressure range (0-1000 mTorr). The equation below gives the  
output current of the pressure:  
16mA  
(
)
(
(
)
)
Ι channel1 = 4mA + p Torr *  
1024Torr  
16mA  
Ι
(
channel2  
)
= 4mA +  
(
p
(
mTorr))  
*
1000mTorr  
Note that for both channels, the output is always between 4mA and 20mA specifically, when the pressure goes  
below 1 Torr, channel 1 current will be approaching its minimum of 4mA and when the pressure is above 1  
Torr, channel 2 current will be 20mA.  
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3.3. RS232/485 With Display  
The HPM-2002-OBE with RS232/485 output and display is shown in the figure below. The user interface  
consists of 4-digit LED display, a status bar, and a mode bar.  
3.3.1.  
Overall Functional Description  
The status bar gives information about the condition of the HPM-2002-OBE. High and Low indicate  
whether the set points are activated. Error indicates if there was a problem downloading the EEPROM. Torr  
and mTorr indicate what pressure regime the gauge is measuring.  
The mode bar indicates which mode has been selected. The HPM-2002-OBE has five modes which the  
user may enter. This is similar to the six modes which can be entered in the standard HPM-2002, there is no  
interlock feature; when the user changes the settings within a mode any adjustments that have been made will be  
permanent once the mode is exited. (To exit without making changes permanent, the user must turn the power  
off.)  
Communication with the serial interface of the HPM-2002-OBE is via an ASCII data string. In the RS-232  
mode the command message consist only of a command string and the terminator. The attention character and  
address string are not required, but if they are used they MUST be valid. If all components of the ASCII data  
string are valid the command will be accepted and executed. The RS-232 mode is sometimes referred to as  
point-to-point mode since only one device may be connected to the controller at any given time.  
A message to the HPM-2002-OBE in the RS-485 mode consists of an attention character followed by the  
address string, the command string, and the terminator. If all components of the ASCII data string are valid the  
command will be accepted and executed. The RS-485 mode is also referred to as multipoint mode since up to  
31 devices may be connected to the same controller in a network scheme.  
3.3.2.  
COMMAND SYNTAX  
In the following examples of syntax codes, the special characters are explained:  
The characters in square brackets [ ] represents a command string, either upper or lower case command  
characters accepted. All characters must follow each other in the string with no spaces or other characters.  
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The characters within wavy brackets { } contain choices for the appropriate command.  
The characters within the symbols < > are the common abbreviations for the one digit ASCII control codes  
which they represent, (e.g. <CR> represents carriage return).  
When entering more than one command in the same data string, they must be separated by a comma.  
All command strings must be followed by the terminator character (carriage return <CR>, also known as  
ENTER).  
When a lower case character is present in an example it represents an option.  
Character Description  
Valid Inputs:  
01 - DF  
1 - 9  
a
RS-485 Address (hexadecimal 0-9, A-F)  
m
Most Significant Digit Of Mantissa  
Decimal Digit  
d
0 - 9  
e
Exponent  
0 - 5  
u
Unit Of Pressure  
T, M, or P  
N/A  
,
Command Separator (comma)  
Command Terminator (carriage return)  
<CR>  
N/A  
3.3.3.  
Interrogation Commands  
Command Description  
Format  
Sample Response  
Transmit Averaged Pressure  
Transmit Pirani Pressure  
Transmit Piezo Pressure  
Transmit RS-485 Address  
Transmit Decimation Ratio  
Transmit Selected Gas #  
Transmit High Setpoint  
Transmit Low Setpoint  
P<CR>Pa: 1.23456e+0 Torr<CR>  
R<CR>Pr: 1.98765e-3 Torr<CR>  
Z<CR>Pz: 7.65432e+2 Torr<CR>  
A<CR>Multidrop Address: 01<CR>  
D<CR>  
G<CR>  
H<CR>  
Decimation Ratio: 255<CR>  
Gas#: 0<CR>  
Hi: 1.00000e+1 Torr<CR>  
L<CR>Lo: 1.00000e-2 Torr<CR>  
S<CR> 00044<CR>  
Transmit Device Status  
Transmit Turnaround Delay  
Transmit Selected Units  
Transmit Software Version #  
T<CR>  
U<CR>  
Comm Delay: 6<CR>  
Torr<CR>  
V<CR>Hastings Instruments-OBE 2002  
Version 1.4 - (7-21-00) <CR>  
Valid Range:  
3.3.4.  
Paramater Modification Commands  
Command Description  
Format  
Modify High Setpoint  
Modify Low Setpoint  
Modify Selected Gas #  
Modify Selected Units  
Modify Decimation Ratio  
Modify RS-485 Address  
H={m.dd}E{+e}<CR> 1.00000e-9 to 9.99999e+9  
L={m.dd}E{-e}<CR>  
G={d}<CR>  
1.00000e-9 to 9.99999e+9  
0 to 4  
(Decimal)  
U={u}<CR>  
D={dddd}<CR>  
*{aa}A={aa}<CR>  
T, or M, or P  
63 to 7936  
1 to DF (Hexadecimal)  
0 to 255(Decimal)  
(Decimal)  
Modify Turnaround Delay *{aa}T={dd}<CR>  
Notes:  
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The setpoints may also be entered as a decimal number, e.g. [H=760.99<CR>] will be same as entering  
[H=7.6099E+2<CR>] .  
When inputting setpoint data, it should be entered in the same Units of Pressure as the presently selected  
Units of Measurement (i.e. Torr, mbar or Pascal). The data is only checked to be a valid number with a one  
digit exponent before being accepted. There are no limit checks on the data; the user is free to choose any value  
appropriate to his use of the instrument.  
The Turnaround Delay and RS-485 address are unique to multipoint communications. In order to prevent  
inadvertent modifications of these parameters, the multipoint attention character and the Model 2002’s present  
address [*{aa}] MUST be used and are checked for validity before the command is executed.  
If the RS-485 address is unknown, the ‘UNIVERSAL ADDRESS’ [*00] may be used to set the address to a  
known value, e.g. [*00A=35<CR>] will change the RS-485 address to 35.  
Caution: Since all units will respond to the ‘UNIVERSAL ADDRESS’, make sure that only the unit to be  
modified is connected to the RS-485 Bus. If more than one unit is connected, this will result in all of the units  
being set to the same address.  
The ‘UNIVERSAL ADDRESS’ is used for setup only; (i.e. to set all units to the same gas #) data is never  
transmitted when the ‘UNIVERSAL ADDRESS’ is used.  
The value entered for the Turnaround Delay is used to modify an internal timer which normally runs at ~8  
millisecond, e.g. [*{aa}T=10<CR>] will set the delay to ~80 milliseconds.  
If the command syntax is not met or if the number is out or range, the HPM-2002 will respond with the  
ASCII codes for <bell>?<CR>, and the command will be ignored.  
3.3.5.  
Calibration Adjustment Commands  
Command Description  
Format  
Valid Range:  
Set Full Scale Calibration  
CF={m.d}E{e}<CR>  
5.12e+2 to 1.023e+3 Torr  
6.83e+2 to 1.365e+3 mbar  
6.83e+4 to 1.365e+5 Pascal  
4.00e+0 to 7.999e+0 Torr  
5.34e+0 to 1.066e+1 mbar  
Set Midpoint Calibration  
CM={m.d}E{e}<CR>  
5.34e+2 to 1.066e+3 Pascal  
Set Low Scale Calibration CL={m.d}E{e}<CR>  
0 to 1.2499e-1 Torr  
0 to 1.666e-1 mbar  
0 to 1.666e+1 Pascal  
Notes:  
The calibration adjustment data may also be entered as a decimal number, e.g. [CF=760.99<CR>] will be  
same as entering [CF=7.6099E+2<CR>].  
When inputting calibration adjustment data, it must be within the valid range of the presently selected Unit  
of Measurement (i.e. Torr, mbar or Pascal). The data is checked to be valid before being accepted.  
If the command syntax is not met or if the number is out or range, the HPM-2002-OBE will respond with  
the ASCII codes for <bell>?<CR> and the command will be ignored.  
The ‘UNIVERSAL ADDRESS’ may be used to calibrate all connected units simultaneously, e.g.  
[*00CF=760<CR>].  
3.3.6.  
Reset / Restore Commands  
Command Description  
Escape  
Format  
<Esc>  
Notes:  
Reset Command Buffer (ignore prior Input)  
Software Reset  
/R<CR>  
Reinitialize Software  
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Restore Factory Defaults  
Set Zero  
/#<CR>  
/0 <CR>  
Restore Calibration Register Default Values  
Store Present Pressure as Instrument ZERO  
(if Piezo <32 Torr & Pirani <50 mTorr)  
Force Zero  
/!<CR> Override Limit Checks and Store Present  
Pressure as Instrument ZERO  
3.3.7.  
Device Status  
When requested to transmit its status the HPM-2002-OBE responds with a five digit number which is  
explained in the following:  
digit#:  
Serial Receiver Overflow  
Main Board EEPROM Error  
Probe EEPROM (any) Error  
1
2
3
4
5
=4  
=2  
=1  
Probe EEPROM Not Responding  
Probe EEPROM Read Error  
=8  
=1  
Probe EEPROM Checksum Error  
Probe EEPROM Verification Error  
Probe EEPROM Identification Error  
=4  
=2  
=1  
Communications Syntax Error  
Piezo Sensor Bad (voltage out of range)  
Pirani Sensor Bad (voltage out of range)  
=4  
=2  
=1  
High Setpoint Alarm (pressure exceeds setpoint)  
Low Setpoint Alarm (pressure less than setpoint)  
Gas# Changed (not the same as when unit last calibrated)  
=4  
=2  
=1  
3.3.8.  
Default RS232/485 Specifications  
Baud Rate.....................................................................................................................................9600  
Character Length .......................................................................................................... Eight data bits  
Parity...........................................................................................................................................None  
Stop Bits.............................................................................................................................................1  
RS 485 Universal Address................................................................................................................00  
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3.3.9.  
Modular Connector Pinout (R2-232) RJ-11 connector on left side.  
Pin #1 ..............................................................................Ready to receive (output signal from OBE)  
Pin #2 .......................................................................................................... Data (output from OBE)  
Pin #3 and #4 ....................................................................................... Common Ground Reference  
Pin #5 .................................................................................................................Data (input to OBE)  
Pin #6 ..........................................................................................Clear to send (input signal to OBE)  
A common application of the RS232 version of the HPM-2002-OBE is to connect the pressure gauge  
directly to the serial port of a PC. This is done by first wiring the supplied communication cable in the manner  
shown below:  
3.3.10. Modular Connector Pinout (RS-485)  
The two RJ-11 Connectors are “Feed Thru” connections, since they are wired in parallel (see above fig.).  
RS 485 half duplex  
RS 485 full duplex  
Pin #1  
Pin #2  
Pin #3  
Pin #4  
Pin #5  
Pin #6  
T+/R+  
T-/R-  
GND  
GND  
n/a  
Pin #1  
Pin #2  
Pin #3  
Pin #4  
Pin #5  
Pin #6  
T+  
T-  
GND  
GND  
R-  
n/a  
R+  
3.3.11. High and Low Set Point Modes  
The HPM-2002-OBE provides TTL outputs for process control. These signals are available on the 15-pin  
connector (see previous table in Section 2.4).  
The High set point can be viewed using either the display or the serial connection. To view the high  
setpoint, place the HPM-2002-OBE in the High mode by pressing the Select button until the High light (on the  
mode bar) is illuminated. The display then shows the set point selected. During normal operation the alarm  
light will illuminate and the TTL output (pin # 1) will go high (+5V) if the pressure exceeds the set point. To  
view the setpoint using the serial connection, send “H<CR>”.  
Similarly, to view the Low set point, place the HPM-2002-OBE in the Low mode by pressing the SELECT  
button until the Low light (on the mode bar) is illuminated. The display then shows the set point selected.  
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During normal operation the alarm light will illuminate and the TTL output (pin # 2) will go high (+5V) if the  
pressure becomes less than the set point.  
To view the setpoint using the serial connection, send “L<CR>”.  
The set points can be adjusted using either the controls on the gauge or the serial connection. To adjust a  
setpoint using the manual controls, place the HPM-2002-OBE in either setpoint mode (High or Low). Next, use  
the ADJUST rotary encoder until the desired setpoint is displayed. Finally, place the HPM-2002-OBE back in  
the Run mode. The new set points are now stored in the HPM-2002-OBE’s memory. Or simply use one of the  
Modify High Setpoint Commands e.g. “H={m.dd}E{=+e}<CR>”.  
3.3.12. Run Mode  
The HPM-2002-OBE will automatically enter the Run mode upon start-up. This is the mode for normal  
operation and the mode in which the instrument will spend most of its time. In the Run mode the HPM-2002-  
OBE will continuously monitor the pressure; update the alarm conditions, and update the display about ten  
times a second.  
3.3.13. Cal Mode  
Optimal performance of the HPM-2002-OBE is achieved by performing in situ adjustments to the  
calibration coefficients in the Cal mode. There are three calibration coefficients. These are the zero coefficients,  
the midrange coefficient, and the atmosphere coefficient. Once a tube has been fully calibrated the midrange  
coefficient should never need further adjustment, but it may be helpful to adjust the zero coefficient or the  
atmosphere coefficient under certain circumstances. The CAL MODE presupposes that the operator is applying  
a known pressure of the correct gas composition (see GAS MODE). The factory calibration points are 800  
Torr, 7 Torr, and < 10-6 Torr. The user’s calibration points are not required to be exactly those values, but  
should be somewhat close, and must be within the ranges shown in the figure on page 15. The HPM-2002-  
OBE detects the voltage signal within the sensor tube, which is converted and displayed as a pressure reading.  
The resulting pressure reading determines which of the three coefficients will be adjusted.  
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3.4. DeviceNet TM  
The HPM-2002-OBE with DeviceNet option is shown in figure below.  
3.4.1.  
Overall Functional Description  
The DeviceNet module consists of a power conversion/sensor transducer board, microprocessor  
board  
and a user interface option board. All communication is conducted via a 5-pin “Micro” style with center pin,  
male pin contacts. The module has passed the ODVA DeviceNet test and conforms to the vacuum/pressure  
gauge device profile; an Electronic Data Sheet (EDS) with limited features is also available upon request.  
3.4.2.  
DeviceNet description  
DeviceNet is a low-level network that provides connections between industrial devices (sensors and  
actuators) and higher-level devices (controllers). Both power and high speed digital signaling are contained  
within the same cable. Controller Area Network (CAN) protocol is used to transfer commands and data across  
the bus. Up to 64 nodes are addressable per network.  
Some of the user benefits of using DeviceNet are:  
Reduced hardwiring and reduced start-up time through the use of standardized cables for the Trunk  
and Branch lines, in addition to standardized Taps for making physical interconnections.  
Ease of integrating products from multiple vendors. More than 250 vendors produce DeviceNet  
products.  
For more information, contact the Open DeviceNet Vendor Association (ODVA) at their web site.  
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3.5. Calibration of the HPM-2002-OBE  
3.5.1. Zero Coefficient Adjustment  
The zero coefficient corrects for the constant power level which is present over the entire pressure range.  
Typically, this adjustment corrects for low pressure errors. The instrument will need to be re-zeroed often if  
measurements are being made in the 10-4 Torr range, especially if the ambient temperature changes. The transducer  
may have a temperature coefficient of up to 2x10-4 Torr/oC. The instrument remote zero input will allow an external  
gauge such as an ion gauge to automatically re-zero the HPM-2002-OBE whenever the pressure drops below the desired  
pressure level (if it has a TTL output).  
NOTE: Do not attempt to zero the Model 2002 in pressures above 10-2 Torr; the microprocessor will not accept a  
zero above this pressure.  
To manually adjust the zero use the following procedure:  
1. If possible, evacuate the vacuum system into the low 10-6 Torr (1.33x10-6 mbar) range or as low as possible  
below 10-4 Torr.  
2. Allow the sensor to operate in this condition for a minimum of 15 minutes.  
3. Place the instrument in the CAL mode, using the “SELECT” button, then turn the “ADJUST” rotary encoder.  
The CAL light will start to flash indicating that the calibration mode has been activated.  
4. Use ADJUST until the display reads 0.0 (or 0.0 with an occasional -0.0). OR using the RS232/485 send  
“/0<CR>”.  
5. The unit is now fully zeroed. Place the HPM-2002-OBE back in the RUN mode to store the zero in permanent  
memory.  
3.5.2.  
Midrange Coefficient Adjustment  
The midrange coefficient corrects for errors in the slope of the power curve of the thin film Pirani.  
Typically, this is due to the geometry of a particular sensor and will only need to be performed once in the  
lifetime of the sensor. This adjustment might be needed if a full calibration is being performed in a gas other than  
nitrogen. The zero adjustment will need to be performed before making this adjustment.  
To adjust the midrange coefficient use the following procedure:  
1. Evacuate the vacuum chamber and refill with the desired gas to a pressure of 7 Torr, as indicated by a  
reference vacuum gauge.  
2. Place the instrument in the Cal mode using the SELECT button.  
3. Turn the ADJUST rotary encoder until the HPM-2002-OBE display matches the reading on the reference  
gauge OR using the RS232/485 send “CM={m.d}E{e}<CR>”.  
4. Place the HPM-2002-OBE back in the Run mode.  
3.5.3.  
Atmosphere Coefficient Adjustment  
If a reference high pressure gauge is not available, the ambient barometric pressure acquired from the  
weather channel or other weather service can be used to adjust the proper reading.  
To adjust the atmosphere coefficient, use the following procedure:  
1. Backfill with the desired gas to a pressure between 700 and 800 Torr.  
2. Place the instrument in the Cal mode using the SELECT button.  
3. Turn the ADJUST rotary encoder until the HPM-2002-OBE display matches the reading on the reference  
gauge OR using the RS232/485 send “CM={m.d}E{e}<CR>”.Place the HPM-2002-OBE back in the Run  
mode.  
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4. Theory of Operation  
The 2002s transducer tube is comprised of two very different sensors which provide a span of measurement  
extending from 1000 Torr down to less than 1 × 10-4 Torr. The piezoresistive device is a direct force sensor  
which provides pressure indication from 1000 Torr down to less than 1 Torr. The thin film Pirani device is a  
thermal conductivity sensor that provides pressure indication from 100 Torr down to less than 1 × 10-4 Torr.  
The two decade overlap in measurement range is convenient for smooth transition either descending or  
ascending in pressure. Both sensors are small micro machined die that are bonded to a Au coated Al2O3 preform  
(stress-isolation) which in turn is bonded to a TO-8 header. The header is resistance welded into a 316 stainless  
steel envelope as shown in the Figure 4.1.  
4.1.1.  
PCB  
EEPROM  
TO-8  
HEADER  
PIRANI  
SENSOR  
PIEZO  
SENSOR  
Figure 4.1  
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4.2. Piezoresistive Sensor  
Figure 4.2 shows a typical schematic of a Boron ion implanted Wheatstone bridge network in a Si  
diaphragm inverted box type geometry. The inside of the box is evacuated during anodic bonding to a Pyrex  
substrate. The membrane has maximum deflection at atmosphere (or higher pressure) and the membrane  
resistances change value as the differential pressure is decreased during pump down. The resulting differential  
output is  
Vo = SPV+V1  
where  
S is the sensitivity  
P is the pressure  
V is the applied bridge voltage  
V1 is the no load output voltage  
Since the sensitivity changes so dramatically with temperature, some correction is required for  
compensation. The change in output voltage  
dVo  
dT  
SdV VdS  
= P  
+
dT  
dT  
To insure temperature invariance,  
dVo  
dT  
= 0  
1 dV  
1
dS  
therefore  
= −  
+
V dT  
S
dT  
which requires for any change in sensitivity to be countered by an equal but opposite change in applied voltage.  
The temperature compensation is a network of temperature dependent resistive components and fixed  
temperature compensation current source compensation, TCR = -TCS.  
Sensitivity of the sensor is proportional to the sensor factor (K), the strain gauge positioning of the  
diaphragm (φ) and the diaphragm geometry (θ) thus S Kφθ. Once the defining geometry of the resistive film  
and piezo membrane have been established, the sensor factor is dependent on the crystal orientation of the  
membrane material, the doping level and diffusion parameters and the strain gauge geometry. The sensor factor  
is essentially the change in resistance for a change in strain or,  
ΔR  
R
ΔL  
K =  
L
Boron ion implanted doped Si matrix resistance elements are employed as shown in Figure 4.2. The die is  
electrostatically bonded on to a Pyrex substrate in a good vacuum so that the die cavity is evacuated; this  
provides maximum deflection at atmospheric pressure. When the sensor is exposed to vacuum the deflection  
becomes less and less as the die cavity pressure and the vacuum system pressure equalizes. Eventually the strain  
in the membrane due to P becomes zero and only the residual strain in the lattice remains. The bridge resistive  
elements are oriented to give maximum change in bridge resistance which in turn gives maximum voltage out for  
a given strain.  
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Figure 4.2  
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4.3. Pirani Sensor  
Figure 4.3a shows a thin metal film resistive element on a one micron thick Si3N4 continuous membrane  
surrounded by a thin film reference resistor on a Si substrate. The membrane is heated to a constant 8 °C above  
ambient temperature that is monitored by the substrate resistor. The membrane resistor is approximately 60 Ω  
and a constant substrate to membrane resistance ratio is maintained. Figure 4.3b shows the Pirani die in cross  
section. A parallel Si lid is eutectically bonded to the Au pads and sits 5 microns above the membrane. As  
shown, this dimension gives a Knudsen number of greater than 0.01 up to atmospheric pressure, which ensures  
a molecular flow component. At 10 Torr the region above the membrane is totally in the molecular flow regime  
and thus provides a relatively linear output verses pressure overlapping the linear output versus pressure of the  
piezo.  
The measurement technique is to produce an output signal that is proportional to the power supplied to the  
heated resistor by using the product of the current and voltage. This rejects errors introduced by resistance  
changes since the sensor resistance is no longer part of the power equation.  
A signal proportional to the power is obtained by multiplying the voltage across the heated sensor and the  
voltage impressed by the direct current across a constant series resistance. The power supplied to the sensor  
resistor must equal the heat dissipated (Et). The three main heat loss routes from the heated sensor are thermal  
conduction through the silicon nitride membrane to the silicon substrate (Es) radiation losses (Er) and thermal  
conduction through the gas to the silicon substrate (Eg); thus, as shown in Figure 4.3b,  
Et = Es + Er + Eg  
The first term, Es, is dependent on the thermal conductivity of the silicon nitride (K), the temperature  
difference (T) between the heater and silicon substrate and geometric factors (AM & L). ES is given by  
Es = (K T Am)/L  
Am is the membrane cross sectional area through which the heat transfer occurs. This is, approximately, the  
outer circumference of the membrane multiplied by the membrane thickness. L is the distance from the edge of  
(Rs) the heated sensor resistor to the silicon substrate.  
For any particular sensor, all of the factors, except T, are constants dependent on its construction. The T  
is held constant by the control circuit. The thermal loss through the silicon nitride will be a constant value  
independent of the thermal conductivity and pressure of the gas.  
Radiation is another source of thermal losses. It can be determined from  
Er = σε(Th4-Ta4)As  
where  
σ = Stefan-Boltzmann radiation constant  
ε = thermal emissivity of the silicon nitride membrane  
AS = surface area of the heated portion of the membrane  
Th = temperature of Rs  
Ta = ambient temperature  
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Figure 4.3a  
Figure 4.3b  
This radiation loss is also independent of the thermal conductivity of the gas. It is somewhat dependent  
upon the absolute temperature of Rs and the ambient temperature, but since T is kept to less than 20 °C, this  
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loss is only approximately 10% of Es. If ambient changes are small compared to the absolute values of the  
temperature this loss can approximated as a constant with temperature.  
Since the first two losses are essentially constant at high vacuum for a given sensor, we can measure these  
losses and subtract them from the input power which leaves only the rate of heat transmission through the gas  
(Eg).  
In the viscous flow regime, the Eg loss is directly dependent on the thermal conductivity of the gas (Kg), the  
surface area of the membrane, the differential temperature and is inversely proportional to distance between the  
membrane and the lid. It can be written as  
Eg = (Kg T As)/x  
The thermal conductivity of the gas is essentially constant when in viscous flow where the Knudsen number  
(Kn) is less than 0.01. In the viscous flow regime there is no change in sensor output with pressure since all of  
the losses are constants with pressure.  
In the molecular flow regime where (Kn > 1) the thermal conductivity of the gas becomes directly  
proportional to the gas pressure as shown below. We can expect then that Eg will be constant at high pressures  
and directly proportional to the pressure at low pressures. The energy loss, Eg, changes between these two  
controlling equations as the system passes through the transition region (0.01 < Kn < 1).  
Eg = arLt(273/Th)1/2(Th-Ta)AgP  
where  
ar = accomodation coefficient  
Lt = free molecule thermal conductivity  
Th = temperature of heated membrane  
Ta = ambient temperature  
P
= pressure  
Ag = surface area of the heated portion of the membrane  
For nitrogen at a pressure of 760 Torr and a temperature of 20 °C the mean free path (λ) is less than 1 x 10-  
7 meters and is inversely proportional to pressure. Since the thermal transfer distance (x) is a few micrometers,  
this sensor will remain in the molecular flow regime at a much higher pressure (10 Torr) than is typical for a  
thermal vacuum gauge. This extends the linear response part of the output curve up into the 1 Torr range. The  
nonlinear transition region will extend up to 1000 Torr.  
4.4. Dual Sensor Operation  
The microprocessor in the control unit continuously monitors the outputs of both the piezoresistive sensor  
and the Pirani sensor. Figure 4.4 shows representations of the sensors output over the pressure range from 10-5  
Torr to 10+3 Torr. The microprocessor uses the output of the piezoresistive sensor at high pressures (>32  
Torr) and uses the output of the Pirani sensor at low pressures (<8 Torr). In the crossover region, a software  
averaging algorithm ensures a smooth transition between the two sensors.  
HPM-2002-OBEVacuum Gauge  
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Figure 4.4  
HPM-2002-OBEVacuum Gauge  
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5. Troubleshooting  
5.1. Advanced Setup Guide  
The HPM-2002-OBE has several setup and control commands which can be accessed by using the  
ADJUST rotary encoder and SELECT pushbutton and at the same time viewing the display. Note that most of  
the commands, which are described below, can be accessed using equivalent RS232/485 commands.  
The advanced setup is accessed from the Run mode. With the Run light illuminated (and not flashing),  
each click of the ADJUST rotary encoder in the clockwise direction will advance the display through each  
command. Once arriving at the desired command, the user can change the parameter (or initiate command) by  
pressing the SELECT pushbutton. When finished with the advanced setup, the user may return to the normal  
Run mode by turning the ADJUST counter-clockwise until the pressure is once again displayed. The  
parameters are not stored upon leaving the command and entering the normal Run mode via ADJUST. To  
make the changes permanent, the SAVE EEPROM command is used. Note that turning the ADJUST clockwise  
indefinitely will simply cycle through the commands.  
Normal Run  
RS485 Address  
Baud Rate  
Data Bits/Parity Bits/Stop Bits  
Turnaround Delay  
Decimation Ratio  
Save EEPROM  
Restore EEPROM  
Restore Calibration  
Restore Factory Defaults  
Software Reset  
Normal Run  
etc…  
The following list gives a description of each of the commands listed above along with the syntax for the  
equivalent RS232/485 command. See RS232/485 section for more details.  
RS485 Address  
A_01  
Multipoint A_01, A_02, … A_FE, A_FF  
The RS485 address is the multipoint address of the HPM-2002-OBE. If the unit is configured for RS232,  
then this parameter must set to a value of E0 or greater.  
(Valid multipoint range 01 to DF)  
*{aa}A={aa}<CR>  
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Baud Rate  
B_2.4  
B_2.4, B_4.8, B_9.6, B_19.2, B_38.4, B_57.6, B_125, B_250, B_500  
The baud rate is given in kbaud. For example, B_9.6 corresponds to a 9600 baud.  
Note: There is no equivalent RS232/485 command.  
Data Bits/Parity Bits/Stop Bits  
P8n1  
8n1, 8n2, 7n2, 7E1, 7E2, 7o1, 7o2, 701, 702, 711,712  
The first character, “8” corresponds to the number of data bits. (e.g. 7 or 8).  
Second character, “n” corresponds to the parity bit. (e.g. n- no parity, E- even parity, o- odd parity, 0-  
space, 1- mark)  
The last character, “1” corresponds to the number of stop bits. (e.g. 1 or 2)  
Note: There is no equivalent RS232/485 command.  
Turnaround Delay  
dt06  
dt00, dt01, ...dtFE, dtFF  
The turnaround delay is unique to multipoint communications. It is the delay between receipt of an  
incoming command to transmission of the response. Each increase in the hex value corresponds to an  
increase in the delay time of approximately 8 ms.  
*{aa}T={dd}<CR>  
Decimation Ratio  
dr5F  
5F, 6F, …, FF  
The decimation ratio can be used to set the amount of sampling which is performed by the HPM-2002-  
OBE’s A/D converters. The higher the value of the hex number, the more sampling takes place before the  
pressure reading is updated. More sampling leads to more stability of pressure readings particularly below 1  
mTorr. However, the increased sampling increases the response time of the gauge to sudden pressure  
changes.  
D={dddd}<CR>  
Save EEPROM  
S_EE  
Save EEPROM stores the calibration parameters which are in the HPM-2002-OBE’s CPU into the HPM-  
2002-OBE’s CPU board’s EEPROM. The CPU board’s EEPROM is not the HPM-2002s tube EEPROM.  
The CPU board EEPROM stores the gauge setup (baud rate, parity, address, set points, gas selection, etc.).  
The HPM-2002s tube EEPROM stores the tube’s calibration parameters.  
EEW<CR>  
Restore EEPROM  
r_EE  
Restore EEPROM transfers the setup from the HPM-2002-OBE’s CPU board’s EEPROM into the HPM-  
2002-OBE’s CPU.  
EER<CR>  
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Restore Calibration  
r_CL  
Restore Calibration transfers the calibration from the HPM-2002s tube EEPROM into the HPM-2002-  
OBE’s CPU.  
EEI<CR>  
Restore Factory Defaults  
r_Fd  
The Restore Factory Default command is used to place calibration parameters into the CPU. From this  
point the gauge can be calibrated. After calibration, the calibration parameters are stored in the HPM-2002s  
tube’s EEPROM.  
/#<CR>  
Software Reset  
rrrr  
This command performs a complete reboot of the HPM-2002-OBE. The CPU is reset and the tube’s  
calibration parameters are loaded.  
/r<CR>  
5.2. Frequently Asked Questions  
Why does my display read, “Err1”?  
This message indicates that an error has occurred during transfer of data between the HPM-2002-OBE’s  
CPU and the sensor tube’s EEPROM where the calibration coefficients are stored. If this error occurs during  
initial startup, then the factory default calibration coefficients will be automatically loaded. The factory  
defaults are often not accurate (typically ±50% or greater), however they allow the user to calibrate the  
gauge. If the sensor tube’s EEPROM cannot communicate with the CPU, then any new calibration will be  
lost when the gauge power is disconnected.  
Sensor tube EEPROM performance can be verified by use of the RESTORE FACTORY DEFAULTS and  
the RESTORE CALIBRATION commands in the following manner. After calibration, use the RESTORE  
FACTORY DEFAULTS command. The pressure reading will shift dramatically. Immediately use the  
RESTORE CALIBRATION command. The pressure reading will return to the calibration value if the tube  
EEPROM communication is working properly. See the advanced setup guide (Section 5.1) for more  
information.  
Why does my display read, “Err2”?  
This message indicates that an error has occurred in the CPU’s EEPROM where the set points, gas number,  
and communication port settings are stored. If this error occurs during initial startup, then the factory default  
values for these settings will be in effect. CPU EEPROM performance can be verified by use of the  
RESTORE EEPROM command. See the advanced setup guide (Section 5.1) for more information.  
Caution: Use of the SAVE EEPROM command at this time will overwrite all previously stored values with  
default values.  
Note: An “Err2” message is a exceedingly rare occurrence. If this error occurs then the CPU’s EEPROM is  
most likely defective.  
Why does my display read, “Err4”?  
This message indicates that a communications error has occurred between the HPM-2002-OBE and a data  
acquisition computer. This error is associated with the serial interface (RS232/485) and can indicate a baud  
rate or parity mismatch, a framing error or an overrun condition. The error can also occur if the data  
acquisition computer is powered down while the HPM-2002-OBE is still connected.  
Modifying as necessary the baud rate, parity, word length and/or the stop bits on either the data acquisition  
computer or the HPM-2002-OBE, usually eliminates this error. Many operating systems are shipped with a  
HPM-2002-OBEVacuum Gauge  
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communications program (e.g. WindowsÔ Hyperterminal) which can be used to communicate with RS232  
versions of the HPM-2002-OBE. The Transmit Device Status (“S<CR>”) command will retrieve the  
HPM-2002-OBE’s status register. A successful read of the status register will clear the “Err4” condition.  
What are Err3, Err5, Err6 and Err7?  
These are simultaneous error conditions, i.e. Err3 = Err1+Err2.  
Why does my display read, “U.U”?  
“U.U” stands for unconnected piezo/unconnected Pirani. This message indicates that the voltage readings  
from the sensors are outside any usable range. Most often this occurs when there is no sensor tube connected  
to the HPM-2002-OBE. This error will also occur if there is a problem with the user’s DC power supply.  
Verify that the voltage supplied to the HPM-2002-OBE is within the specified range using a voltmeter at  
pins 3 and 4 on the power cable. After power verification and with the voltage still applied, hot plug the cable  
into the HPM-2002-OBE. If the “U.U” still appears, most likely the sensor tube (HPM-2002s) needs to be  
replaced.  
Why does my display read, “U .”?  
“U.” stands for unconnected piezo. This message indicates that the voltage reading from the piezoresistive  
sensor is outside any usable range. While this message can mean that the sensor tube (HPM-2002s) will  
need to be replaced, it can also indicate that the piezo zero calibration parameter, which is stored in the  
sensor tube’s EEPROM, has become corrupted or lost. (See next FAQ)  
Why does my display temporarily show, “U .” as I pump the system down?  
“U .” stands for unconnected piezo. This message may flash near the dual sensor crossover pressure range if  
the piezo zero calibration parameter has been corrupted or lost.  
The RESTORE CALIBRATION command will download the calibration parameters from the HPM-2002-  
OBE to the sensor tube. See the advanced setup guide (Section 5.1) for more information. If the error  
persists at the crossover point, then a calibration of the Piezo sensor should be performed. The Piezo Zero is  
updated when the Pirani pressure is less than 125 mTorr. In order to update and save the Piezo Zero  
parameter:  
Pump out to 100 mTorr or less  
Using SELECT, step to the CAL function  
Rotate ADJUST one step in either direction and then back to its original position (CAL light starts  
flashing)  
Using SELECT, exit the CAL function and return to the Run mode  
Changing the Piezo Zero will shift the atmospheric reading by the same amount. therefor the atmospheric  
readong should also be checked and re-adjusted if necessary.  
Why does my display read, “. U”?  
This message indicates that the voltage readings from the thin film Pirani sensor are outside any usable  
range. This usually indicates that the sensor is defective and will need to be replaced.  
HPM-2002-OBEVacuum Gauge  
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6. WARRANTY  
6.1. Warranty Repair Policy  
Hastings Instruments warrants this product for a period of one year from the date of shipment to be free  
from defects in material and workmanship. This warranty does not apply to defects or failures resulting from  
unauthorized modification, misuse or mishandling of the product. This warranty does not apply to batteries  
or other expendable parts, or to damage caused by leaking batteries or any similar occurrence. This warranty  
does not apply to any instrument which has had a tamper seal removed or broken.  
This warranty is in lieu of all other warranties, expressed or implied, including any implied warranty as to  
fitness for a particular use. Hastings Instruments shall not be liable for any indirect or consequential  
damages.  
Hastings Instruments, will, at its option, repair, replace or refund the selling price of the product if Hastings  
Instruments determines, in good faith, that it is defective in materials or workmanship during the warranty  
period. Defective instruments should be returned to Hastings Instruments, shipment prepaid, together with a  
written statement of the problem and a Return Material Authorization (RMA) number.  
Please consult the factory for your RMA number before returning any product for repair. Collect freight will  
not be accepted.  
6.2. Non-Warranty Repair Policy  
Any product returned for a non-warranty repair must be accompanied by a purchase order, RMA form and  
a written description of the problem with the instrument. If the repair cost is higher, you will be contacted for  
authorization before we proceed with any repairs. If you then choose not to have the product repaired, a  
minimum will be charged to cover the processing and inspection. Please consult the factory for your RMA  
number before returning any product repair.  
TELEDYNE HASTINGS INSTRUMENTS  
804 NEWCOMBE AVENUE  
HAMPTON, VIRGINIA 23669 U.S.A.  
ATTENTION: REPAIR DEPARTMENT  
TELEPHONE  
TOLL FREE  
FAX  
(757) 723-6531  
1-800-950-2468  
(757) 723-3925  
E MAIL  
INTERNET  
Repair Forms may be obtained from the “Information Request” section of the Hastings Instruments web  
site.  
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7. Diagrams and Drawings  
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