Det-Tronics 505 Combustible Gas Detector Transmitter with Combustible Gas Sensor CGS User Manual
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3.1
1. Use formula: C x K = S
C = Concentration of calibration gas in % LFL = 50
K = K-factor from Table 1 in 76-1017 = 1.44
50 x 1.44 = 72
S = 72
2. Use formula: (S x 0.0067) + 0.17 = S1
S = span output level (determined in step 1) = 72
(72 x 0.0067) + 0.17 = S1
(72 x 0.0067) = 0.48
0.48 + 0.17 = 0.65
S1 = 0.65
3. Calibrate the Model 505 for a reading of 0.65 Vdc on
the voltmeter with a calibration mixture of 50% LFL
methane applied to the sensor.
NOTE
This procedure applies only to the Model 505
Transmitter. Other Det-Tronics transmitters use the
standard K-factor formula.
Table 2—Calibration Procedure
WARNING
Before removing the junction box cover, verify that no dangerous levels of gas are present.
Step
Switch Position
Operator Action
1
CAL/NORM switch in the CAL position.
1. LED turns on.
2. Connect a digital voltmeter to the transmitter test jacks.
3. Set the meter range to 2 Vdc.
2
ZERO/SPAN switch in the ZERO position.
1. Adjust the ZERO potentiometer to read 0.000 Vdc on the
voltmeter. See Note 3 below.
3
ZERO/SPAN switch in the SPAN position.
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.
4
ZERO/SPAN switch in the ZERO position.
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.
5
CAL/NORM switch in NORM position.
1. The LED turns off.
2. The calibration is complete.
3. Replace the junction box cover.
NOTES:
1. When the CAL/NORM switch is in the CAL position, the yellow LED turns on and the 4 to 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.