Sierra Monitor Corporation 5100-06-IT - Manual (Page 6)

Model 5100-XX-IT Toxic Gas Sensor Module
Page: 2
1.2 PRODUCT CONFIGURATION
Various module mounting configurations can be implemented without special fixtures. Where applicable,
these options are factory configured prior to shipment. Mounting configuration can be selected by the installer
or field technician and are fully described in this manual. Sensor must always be oriented downward.
1.3 THEORY OF OPERATION
Electrochemical sensors are fuel cell-like devices consisting of an anode, cathode, and electrolyte. The
components of the cell are selected so a subject gas, allowed to diffuse into the cell, will cause a chemical
reaction and generate a current. The cells are diffusion limited so the rate the gas enters the cell is solely
dependent on the gas concentration. The current generated is proportional to the rate of consumption of the
subject gas in the cell.
Sierra Monitor electrochemical sensors provide improved reliability by allowing the gas to diffuse into the
sensor through a capillary port, rather than diffusing through membranes. The result is an extremely stable
sensor with very low temperature and pressure coefficients and the capability to monitor gas as ppm.
1.4 MODES OF OPERATION
1.4.1 SENTRY INTERFACE
IT gas sensor modules can be installed on Sierra Monitor Sentry Model 5000 controllers Ver. 6.XX MFD
after 9/1/95. When it is installed in a Sentry system the IT module must have a unique address which can
be established by setting an address between 1 and 8 on the Module Address Switch accessible from the
cover plate as illustrated in Figure 4-2. Figure 4-7 in this manual provides the wiring terminations for
connections to the Sentry controller.
Note 1: The Model # 5100-88-IT CO2 gas sensor module range is 0-5000 ppm. Therefore, the Sentry
Controller must be configured for a 0-100 % full scale input. The Sentry does not have the ability to
display engineering units up to 5000. The alarm set points need to be set as a percentage of full
scale. Example, a 2500 ppm alarm set point is equal to 50% scale.
When the module is operated in conjunction with a Sentry controller, the alarm relay setup (See section
5.3) should be set to “Sentry”, allowing the Sentry controller to manage alarm relay action rather than the
5100-XX-IT Gas Sensor Module.
1.4.2 MODBUS OPERATION
An RS-485 Modbus RTU serial interface allows direct connection to standard PLCs and DCSs. The
Module Address Switch (section 4.5) allows the user to select up to 15 different Modbus addresses. Also,
an additional 254 Modbus addresses are available via menu selection. Figure 4-7 in this manual provides
the wiring terminations for Modbus connections. The 5100-XX-IT provides the wiring terminations for
Modbus connections.
1.4.3 ANALOG OPERATION
The analog 4-20 mA interface allows direct connection to standard controller and distributed system. The
module is an active current source.
The standard configuration is set up for a 3-wire non-isolated connection. An optional 4-wire isolated
connection is also available and can be enabled by changing JP1 and JP2. (Figure 4.6)
1.4.4 REMOTE SENSOR (APPENDIX D)
The Remote Sensor option can be used to remotely mount some sensors up to 15’ from the transmitter
(refer to Appendix D for allowable distances).
1.4.5 HART CONNECTION (APPENDIX F)
A HART interface option is available. Refer to Appendix F for information.