Sierra Monitor Corporation Carbon Monoxide Alarm TR 005 User Manual

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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