ENMET ISA-44-2OD - Manual (Page 15)

ISA-44-2-OD ENMET Corporation
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3.4 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 panel, specifies the voltage for each sensor. Refer to Figures 3 and 4 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 OPERATION switch to PURGE ON and adjust RV38 (purge POT) to the voltage specified on the chart
inside the unit.
N
OTE : Adjust this POT clockwise to increase, counterclockwise to decrease the voltage.
2. Turn the OPERATION 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 4) 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.
3.5 Oxygen Cell Adjustment
1. Expose the cell to fresh air for 15 minutes.
2. Adjust the Oxygen Gain Potentiometer (front of enclosure) until the meter reads 20.9% oxygen. This is the
normal fresh air concentration. Use a screwdriver to adjust the potentiometer.
3. Turn the HORN back ON.
4. You must adjust the Oxygen cell periodically since atmospheric conditions change. Do this at least every time
you run a safety check on your monitoring equipment.
N OTE : Try not to locate the unit in an area where quick temperature changes are likely to occur, like near an outside
door. The oxygen cell is sensitive to temperatures, and the circuitry for this cell cannot track rapid changes in
temperature. Such a change may cause nuisance alarms, especially for those units calibrated to alarm at a
percent near the normal fresh air volume (20.9%). A rapid temperature change is more likely to cause an alarm
on a unit calibrated to alarm at 19.5% than one calibrated to alarm at 18.0%.