Sierra Monitor Corporation 5000 instruction manual SMC sierra monitor corporation, SERVICE Page

SMC sierra monitor corporation		Sentry Instruction Manual - Version 6
7.5 COMBUSTIBLE GAS SENSOR MODULE
(5100-02)
7.5.1 DESCRIPTION
The Combustible Gas Module includes the sensor
and electronic assembly installed in an explosion
proof housing. The sensor screws into one hub of
the enclosure and plugs into the bottom
electronics card via a six pin connector. Cabling
to the controller connects to a three pin spring
loaded terminal strip.
7.5.2 TROUBLE ANALYSIS
Electrical adjustment, or replacement of the
sensor will be necessary under the following
conditions:
	• Controller displays the following error
	messages:
	CHK BRIDGE VOLT
	SENSOR FAILURE
	LOW SENSITIVITY
	• False readings or alarms are received
	due to sensor inaccuracy.
Warning: : During sensor adjustments the
		Figure 7-6
concentration reading on the controller will be		Cover Plate - Combustible Gas Module
inaccurate and alarm level concentrations may be
displayed. If false activation of the alarm relays
will cause a problem disconnect the relay wiring		Comparing to the "GND" (ground) test point measure
prior to adjustment or turn the module off using the
		"BRIDGE VOL" (bridge voltage) and adjust to 2.00 VDC
CHANGE MODULE mode.
		using "BRIDGE ADJ" potentiometer. Turn counter-
	NOTE	clockwise to increase.
	Although all the necessary data can be collected with a
	voltmeter at the sensor module, some helpful information	7.5.3.2 ZERO ADJUSTMENT
	can be displayed or printed. See diagnostic codes 0004
	and 0008 in Appendix C.	Comparing to ground measure SIGNAL OUT and adjust to
7.5.3 ADJUSTMENT PROCEDURE		0.18 VDC by turning ZERO ADJ potentiometer. Turn
		counter clock-wise to increase.
Prior to reading voltages and making adjustments perform
a visual inspection to confirm that there are no physical		7.5.3.3 SPAN ADJUSTMENT
problems such as water in the electronics enclosure,
		1. Determine the concentration of the calibration
wiring damage or corrosion.
Use Figure 7-6 to locate test points during the following		gas (CG) in % LEL.
		2. Use the following formula to determine the
procedures:
Caution: The area must be free of flammable vapors or		response to the calibration gas at SIGNAL OUT.
		Voltage (Signal Out) = (CG+12)/60
gases during any adjustments or maintenance procedures.
		For Example:

7.5.3.1 BRIDGE VOLTAGE ADJUSTMENT

Confirm that no combustible gas is present and remove sensor module cover.

If CG = 50% L.E.L Signal Out = (50+12)/60

= 1.03 volts

SERVICE Page: 69