CY7/670 Series Temperature Sensors
Application Notes
M-4447/0307
An excessive heat flow through the connecting
leads to any temperature sensor can create a
situation where the active sensing element (for the
CY7/670 series this is the diode chip) is at a
different temperature than the sample to which the
sensor is mounted. This is then reflected as a real
temperature offset between what is measured and
the true sample temperature. Such temperature
errors can be eliminated by proper selection and
installation of the connecting leads.
INSTALLATION AND OPERATION
Three aspects of using a temperature sensor are
critical to its optimum performance:
• the proper electrical and thermal installation of
the connecting leads that run to the sensor
• the actual mounting of the sensor to the sample
assembly
• the measurement electronics used for reading
and recording temperature data from the sensor
In order to minimize any heat flow through the
leads, the leads should be of small diameter and
low thermal conductivity. Phosphor-bronze or
manganin wire is commonly used in sizes 32 or 36
AWG. These wires have a fairly poor thermal
conductivity yet the resistivities are not so large as
to create any problems in four-wire
Connecting Leads
Although the majority of the CY7/CY670 series
sensors are two-lead devices, measurements are
preferably made using a four-wire configuration to
avoid all uncertainties associated with lead
resistance. This is done by using four connecting
leads to the device and connecting the V+ and I+
leads to the anode and the V– and I– leads to the
cathode as shown in Figure 1. The exact point at
which the connecting leads are soldered to the
device leads results in negligible temperature
measurement uncertainties.
measurements.
Lead wires should also be thermally anchored at
several temperatures between room temperature
and cryogenic temperatures to guarantee that heat
is not being conducted through the leads to the
sensor. A final thermal anchor at the sample itself
is a good practice to assure thermal equilibrium
between the sample and the temperature sensor.
Note that the CU, CY, SO, and DI mounting
adapters serve as their own sample thermal
anchor.
In a two-wire measurement configuration, the
voltage connections (point A in Figure 1) are made
near or at the current source, so only two leads
are actually connected to the device. Some loss in
accuracy can be expected since the voltage
measured at the voltmeter is the sum of the diode
voltage and the voltage drop across the
connecting leads. The exact temperature
uncertainty will depend on the temperature range
and lead resistance. For a 10-ohm lead
resistance, the diode voltage will be offset by 0.1
mV, which gives a negligible temperature error at
liquid helium temperature but a 50 mK error near
liquid nitrogen temperature. Note the PI and CY
adapter can be used only in a two-wire
I the connecting leads have only a thin insulation
such as vinyl acetal or other varnish type coating,
a simple thermal anchor can be made by winding
the wires around a copper post or other thermal
mass and bonding them in place with a thin layer
of CYAV varnish. There are a variety of other
ways in which thermal anchors can be fabricated;
a number of guidelines can be found in detail in
the following references.
configuration.
Figure 1. Four-Wire Configuration for CY7/670 Series Sensor Installation
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CY7/670-LR
The gold-coated copper LR adapter is designed
3. Lift the edge of the clip using a small pair of
pliers or screwdriver.
for insertion into a 1/8-inch diameter tube. A thin
layer of CYAG grease should be applied to the
copper adapter before insertion. This eases
installation at room temperature and enhances the
thermal contact.
4. Slide the SD package into place underneath
the clip and gently lower the clip onto the lid of
the SD package. Note that a slot is cut
underneath the clip to accept the SD package.
Refer to the drawing for details.
If the device is to be used only below 325 K, a
layer of CYAG grease should be used between
the SD package and mounting surface to enhance
the thermal contact.
CY7/670-CU/DI/CY
The gold-coated copper CU, DI and CY adapters
serve as both a sensor and a thermal anchor
assembly. These adapters are designed to be
mounted to a flat surface using a 4-40 brass
screw. Avoid over-tightening the screw; use only
enough force to firmly hold the sensor in place.
Brass is recommended for the screw as the
differential thermal contraction between the
adapter and the screw will cause the mounting
assembly to tighten as opposed to loosen when
the system is cooled. A thin layer of CYAG grease
should be used to enhance the thermal contact
between the adapter and the mounting surface.
Sensor Operation
Temperature controllers and thermometer
instrumentation offered by Omega Engineering,
Inc. are designed to be directly compatible with the
CY7/670 series sensor to give optimum
performance and accuracy together with direct
temperature readouts. Simply follow the
instructions provided with the instrument
concerning sensor connection and instrument
operation. If a user-supplied current source,
voltmeter, or other instrumentation is going to be
used with the CY7/670 series sensor, special
attention should be given to the following details.
The CU adapter has four color-coded leads: red
(I–), green (V–), clear (V+), and blue (I+). The CY
adapter has two color-coded leads: yellow (+) and
green (–). The green lead on the DI adapter is the
cathode.
The CY7/670 series sensors are designed to
operate at a constant current of 10 µA while the
voltage variation with temperature measurement
depends directly on the specifications of the
current source and the voltmeter. A current source
operating at the level of +0.01 µA (±0.01 K) is
probably suitable for most applications. The
voltmeter resolution required can be estimated
from the sensitivity (dV/dT) of the CY7/670 sensor:
CY7/670-ET/MT
Both adapters are gold-plated copper hex head
bolts with the SD package mounted in a slot on
the adapter head. The ET adapter screws into a ¼
inch deep, 6-32 threaded hole while the MT
adapter screws into a 6 mm deep, 3 × 0.5 mm
threaded hole. Before assembly, the threads
should be lightly greased with CYAG grease. Do
not over-tighten, since the threads are copper and
can be easily sheared. Finger-tight should be
sufficient.
Temperature
Sensitivity
(mV/K)
2.4
(K)
305
77
1.9
4.2
33
Multiplying the above sensitivity by the desired
temperature resolution in K will give the required
voltage resolution in mV.
CY7/670-BO
The BO adapter should be mounted in the same
manner as the CU. The BO adapter contains its
own thermal anchor and is an epoxy-free
assembly.
The static impedance of the CY7/670 series
sensor operating at 10 µA current is on the order
of 100,000 ohms. Therefore, the input impedance
of the voltmeter must be significantly larger than
this to avoid measurement errors. Voltmeters with
input impedances of greater than 109 or 1010
ohms should be used.
CY7/670-CO
The CO adapter is used to attach the CY7/670-SD
package to a flat surface. The adapter is a spring-
loaded clamp designed to maintain pressure on
the SD package as the temperature is varied.
Good quality instrumentation must be used and all
instrumentation and wiring should be properly
grounded and shielded. Temperature
measurement errors will result if there is excessive
AC noise or ripple in the circuitry. Further details
can be found in the article by Krause and Dodrill
given in the references.
1. Remove the hold down cap that holds the
three-piece CO assembly together. The CO
assembly should appear as shown in the
accompanying drawings.
2. Bolt the assembly into a 4-40 threaded hole.
The stop on the brass screw should rest
against the mounting surface and it also
prevents overcompressing the spring.
Note: All materials mentioned above that are used
in sensor installation are available from OMEGA
Engineering, Inc.
3
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REFERENCES
Krause, J.K. and Swinehart, P.R. (1985). Demystifying Cryogenic Temperature Sensors. Photonics Spectra. August, 61–68.
Krause, J.K. and Dodrill, B.C. (1986). Measurement System Induced Errors in Diode Thermometry. Review of Scientific
Instruments 57 (4), 661–665.
Sparks, L.L. (1983). Temperature, Strain, and Magnetic Field Measurements. In Material at Low Temperatures, Ed. By R.P. Reed
and A.F. Clark. American Society of Metals, Metals Park, 515–571.
White, G.K. (1979). Experimental Techniques in Low Temperature Physics. Clarendon Press, Oxford.
CY7/670-SD
CY7/670-ET
CY7/670-BO
CY7/670-CU/DI
Basic sensor soldered onto SAE-
threaded copper adapter.
Temperature range: 1.4 to 325 K
Mass: 1.4 g
Basic sensor mounted into
bolt-on disk with leads thermally
anchored to disk with low
temperature epoxy. CU version is
4-lead. DI is 2-lead.
Basic sensor package style.
Temperature range: 1.4 to 475 K
Mass: 0.03 g
Basic sensor soldered onto bolt-on
copper block with leads thermally
anchored to block.
Temperature range: 1.4 to 325 K
Mass: 1.5 g
Temperature range: 1.4 to 325 K
Mass (excluding leads): 4.3 g
CY7/670-CO
CY7/670-CY
CY7/670-LR
CY7/670-MT
Basic sensor soldered into
cylindrical copper adapter.
Temperature range: 1.4 to 325 K
Mass: 0.15 g
Basic sensor with spring-loaded
brass clamp to hold sensor to
sample.
Temperature range: 1.4 to 475 K
Mass (without sensor): 1.7 g
Basic sensor soldered into metric-
threaded copper adapter.
Temperature range: 1.4 to 325 K
Mass: 1.4 g
Basic sensor epoxied into
relatively large copper disk. 30
AWG stranded copper lead pair is
thermally anchored to disk.
Temperature range: 1.4 to 325 K
Mass (excluding leads): 4.3 g
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