Det-Tronics 505 Combustible Gas Detector Transmitter with Combustible Gas Sensor CGS - Manual (Page 11)

8 95-8472 3.1
SENSOR VOLTAGE ADJUSTMENT
The combustible gas sensor is designed to operate at
3.3 Vdc. Voltages greater than this will shorten sensor
life, while voltages less than this will reduce sensor
sensitivity. The sensor supply voltage potentiometer
is adjusted at the factory to deliver 3.3 volts when the
sensor is coupled directly to the transmitter housing.
However, if the sensor and Model 505 Transmitter
are located separately, and the distance exceeds
the recommended distance indicated in Table 1, re-
adjustment is necessary. To adjust sensor voltage,
connect a digital voltmeter across the white and black
sensor wires (at the sensor).
Adjust the sensor voltage potentiometer (see Figure 8)
to obtain a reading of 3.3 Vdc on the meter. For sensor
separation configurations, this is typically a two-person
procedure.
Always measure the sensor voltage whenever utilizing
a sensor separation kit, and any time a Model 505
transmitter has been replaced. Failure to deliver 3.3 Vdc
to the sensor will result in loss of system accuracy.
CAUTION
The voltmeter must be suitable for use in a
hazardous location.
NOTES
1. SHIELDED SENSOR WIRING CABLE REQUIRED.
2. GROUND SENSOR WIRE SHIELD AT TRANSMITTER END ONLY.
3. SHIELDS SHOULD BE STRIPPED BACK WITHIN JUNCTION BOXES.
4. TERMINAL CONNECTOR REQUIRED FOR SENSOR CONNECTION
4. (PROVIDED WITH SENSOR TERMINATION BOX).
SENSOR LOCATION
TRANSMITTER
LOCATION
CONNECT KEYED SENSOR
PLUG TO PIN CONNECTOR
CONTROLLER
4 TO 20 MA
24 VDC
–
–
+
+
C1939
–
SIG
RED
SENSOR
WHT BLK
+
RED WHT
BLK
Figure 7—Model 505 Transmitter with Sensor Termination Box
Table 1—Maximum Sensor Separation Distances
Wire Size
(AWG)
Recommended
Maximum Transmitter to Sensor Distance*
Maximum Transmitter to Sensor Distance**
Feet Meters Feet Meters
20 12 3.6 65 19
18 20 6.1 100 31
16 31 9.4 160 50
14 50 15.2 260 79
12 78 24.0 410 126
* Transmitter voltage adjustment not required.
** Transmitter voltage adjustment is required.