Technical Reprint TR-005
Gas Detection Systems
How to make your facility's monitoring data accessible
by Gordon Arnold
You really have to have back-
bone to survive in the safety
monitoring world today. No,
there is no heavy lifting re-
quired. I am referring to the
data backbone of the facility,
plant or process to which the
monitoring system is applied.
In times past, gas monitor-
ing systems were free-stand-
ing, and any data they gen-
erated was collected and used
on a local basis. Today, plants
and other facilities most likely
require that all data be cen-
tralized so monitoring sys-
tems can perform their func-
tions and provide data to
higher-level systems. Data must be accessible
on plant-wide backbones, which come in many
flavors.
For purposes of meeting future requirements
to integrate data to a facility backbone, this
minimum system with serial communications
is now well on the way to plant-wide integra-
tion. At the Control level the system provides
sensor monitoring and also controls the alarm
activities. At the Information level data can be
retrieved from the controller via the serial con-
nection. The facility IT group, plant process
control team or the building automation con-
sultants are now free to investigate opportu-
nities to interface to the gas detection system
via the plant backbone.
In addition to various proprietary data busses,
some plant backbones are serial-based
(Modbus RTU, DF1, Metasys), many are based
on Ethernet architecture (Modbus TCP,
EtherNet/IP, BACnet/IP) and others are based
on fieldbusses such as Profibus, DH+ and
ControlNet. This discussion is confined to se-
rial data busses and Ethernet networks, but
the principals and issues are universal.
A strong backbone
The terms “serial communication” or “Ethernet”
describe only the electrical hardware charac-
teristics of the backbone, such as the type of
wires and the methods of connection. Com-
paring to an office equipment environment, a
serial connection would interface a computer
to a modem, while an Ethernet connection
would network the computer and allow it to
communicate with a server, a network printer
or many other devices. The aspect that is not
yet described is the protocol, which is the data
format and handling instructions that travel
on the backbone.
The challenge for industrial hygiene profes-
sionals is to determine which backbone inter-
face is required and then ensure that the se-
lected equipment meets that requirement.
Figure 1 represents the minimum requirements
for a gas detection system that are generally
well understood. The system must include gas
detection modules, a method to communicate
to a controller, flexible alarm handling with relay
outputs, and a method for communicating data
to higher-level systems. In this case, serial
communications are used to provide data to a
dedicated computer.
Sierra Monitor Corporation 1991 Tarob Court Milpitas, CA 95035 USA (408) 262-6611 (800) 727-4377 Fax: (408) 262-9042
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