ENMET ISA-M - Manual (Page 9)

ISA – M ENMET Corporation
7
4.4 Sensor Heater Voltage
Heating the sensor promotes the oxidation reaction on the element surface. The temperature to which the sensor
element is heated determines the selectivity of the equipment to certain gases.
A chart, located inside the instrument front cover, specifies the voltage for the sensor. Units requiring purging have
two voltages specified. Refer to Figure 2 for potentiometer locations.
N OTE : Do not increase any sensor voltage to values greater than those given on the chart. Too high voltage can
damage the sensor heater winding; and if that happens you have to replace the sensor.
Y OU NEED :
§ A digital voltmeter with a + or - 0.05% accuracy
§ A small screwdriver for adjusting pots.
Measure DC volts across the brown and orange wires in the sensor assembly at the sensor, not at the terminal strip.
EXCEPTION : If your sensor is mounted directly onto the side of the enclosure, then measure DC volts at the terminal
strip -- TB1-7 (ground) and TB1-6 (heater).
S ENSORS REQUIRING PURGING :
1. Turn the switch to PURGE ON and adjust RV38 (purge POT.) to the voltage specified on the chart inside the unit
(see Figure 2). NOTE: Adjust this pot. clockwise to increase, counterclockwise to decrease the voltage.
2. Switch to HORN OFF .
3. Now adjust the sensor heater pot . RV32 to the required voltage.
N OTE : Adjust this pot. clockwise to increase, counterclockwise to decrease the voltage.
S ENSORS NOT REQUIRING PURGING :
Adjust the sensor heater pot. (RV32; see Figure 2) to the required voltage.
N OTE : Sometimes, if a sensor is located a great distance from the control unit, the heater adjust may not, by itself,
be able to bring the voltage to the required reading. If not, then adjust the purge adjust pot., RV38, to arrive
at the necessary voltage.
N OTE : Once you have set the voltage at the sensor, check and record the voltage across TB1-7 (ground) and TB1-6
(heater). The next time you must check the sensor heater voltage, first check the voltage across TB1-7 and
TB1-6. If this voltage has not changed, the sensor heater voltage at the sensor has also not changed. If the
voltage across TB1-7 and TB1-6 has changed, you must reset the voltage at the sensor as described in the
procedures above.