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cAlibrAtion
model 505
The Model 505/CGS must be calibrated when the
system is commissioned as well as when the CGS
sensor is replaced. Calibration is performed at the
Model 505 using the following procedure. Calibration
at the UD10 is not supported.
Before removing the junction box cover, verify that no dangerous levels of gas are present.
Step
CAL/NORM switch in the CAL
1
position.
ZERO/SPAN switch in the ZERO
2
position.
ZERO/SPAN switch in the SPAN
3
position.
ZERO/SPAN switch in the ZERO
4
position.
CAL/NORM switch in NORM
5
position.
NOTES:
1. When the CAL/NORM switch is in the CAL position, the yellow LED turns on and the 4-20 mA output signal goes to 3.4 mA.
2. The voltmeter must be suitable for use in a hazardous location.
3. if the possibility of background gases exists, purge the sensor with clean air prior to the zero adjustment to assure accurate
calibration.
4. A typical sensitivity reading with 50% LFL gas applied to the sensor is 35 to 50 millivolts for a new sensor. Sensor replacement
is recommended when the sensitivity reading is less than 15 millivolts.
5. if a dust cover or splash shield is used, inspect it to be sure that it is not dirty or plugged. A plugged dust cover can restrict
the flow of gas to the sensing element, seriously reducing its effectiveness. For optimum performance, sensor covers/filters
should be replaced frequently to ensure that they are not degraded or plugged.
4.3
Switch position
ZERO/SPAN SWITCH
SENSOR VOLTAGE ADJUST
CAL/NORM SWITCH
CALIBRATE LED
4 mA ADJUST
WarnIng
Operator Action
1. LED turns on.
2. Connect a digital voltmeter to the transmitter test jacks.
3. Set the meter range to 2 Vdc.
1. Adjust the ZERO potentiometer to read 0.000 Vdc on the
voltmeter. See Note 3 below.
1. Adjust the 4 mA potentiometer to read 0.167 Vdc on the
voltmeter.
2. Apply the 50% LFL calibration gas to the sensor. When the
output has stabilized, adjust the SPAN potentiometer for a
reading of 0.500 on the voltmeter.
1. Sensitivity test. The meter must read greater than 0.015 Vdc.
See Note 4 below.
2. Remove the calibration gas.
3. When the meter reads 0.002 Vdc or less, remove the test
probes.
1. The LED turns off.
2. The calibration is complete.
3. Replace the junction box cover.
H-3
ZERO ADJUST
SPAN ADJUST
TEST POINTS
A1944
95-8618
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