SMC sierra monitor corporation Sentry Instruction Manual - Version 6
SERVICE
Page: 70
3. Using a Sierra Monitor Model 1200-26 Gas
Calibrator with a Sierra Monitor Model 5358-00
calibration adapter, or Model 5360 Gas
Delivery Fitting. Apply the calibration gas at a
flow rate of 100 cc/min. until the signal out
voltage stops changing (approx. 2 minutes).
Then adjust span adj. potentiometer to the
calculated value.
4. Remove the calibration gas and wait for the
voltage to drop. If the voltage is below 0.30
VDC the procedure is complete. If the voltage
is above 0.30 VDC repeat the zero and span
adjustments.
5. Calibrate the sensor using the instruction manual
procedure.
• A LOW SENSITIVITY message during
calibration indicates one of the two
conditions for a combustible sensor:
• The zero gas voltage must be less than
.3 volts.
• The new span change (span voltage less
zero voltage) must exceed 30% of the
calculated span change.
For Example:
Zero gas voltage = .20 VDC
Span voltage = .43 VDC
Span change is .43-.2 = .23 VDC
As the calculated span value (from step
5 above) is 1.03, the calculated span
change is: 1.03-.2 = .87
By calculation: 30% of .87 = .26
The new span change (.23) is less than
30% of the calculated span change so a
LOW SENSITIVITY message will be
displayed.
The LOW SENSITIVITY calculation is made to insure that
the calibration does not adjust the electronics so that the
"gain" is large enough to cause false alarms due to minor
drift or due to minimal electronic noise.
7.5.4 SENSOR REPLACEMENT
If any of the above adjustments cannot be completed
successfully the sensor and/or electronics will require
replacement. To check the sensor unplug it from the
electronics and remove from the housing so that continuity
and resistance tests can be made. Table 7-4 provides the
pin out for the sensor assembly.
PIN FUNCTION WIRE COLOR
1 DETECTOR WHITE
2 COMPENSATOR BROWN
3 CALIB. SW. RED
4 DETECTOR BLACK
5 DRAIN BARE
6 CALIB. SW. GREEN
Table 7-5
Combustible Gas Sensor
Wiring Pin Out
1. Detector element resistance should be between 1.5 to
2 ohms.
2. Compensator element resistance should be between
1.5 to 2 ohms.
3. Calibration switch should be open in normal
operation and should close when the calibration
magnet is applied.
If the sensor fails any of these tests it should be replaced.
If the sensor passes these tests the electronics are suspect
and BOTH the sensor and electronics should be replaced.
(The electronics and sensor which are removed should be
returned to the factory for evaluation).
When a new sensor is installed the following actions must
be taken:
• Make the bridge voltage adjustment
immediately to avoid over-voltage damage to
the sensor.
• Use diagnostic code 0020 to establish nominal
value calibration.
• Allow 24 hours for full stabilization of the
sensor, recheck the zero and span adjustments
and calibrate the sensor module.