ENMET ISA-44-2OD - Manual (Page 24)

ENMET Corporation ISA-44-2-OD
20
5.3 Replacement of Sensors
Gas Sensors
The MOS sensor is durable , it can be purged of contaminants by operating in PURGE for a sufficient length of time
and at regular intervals.
Gross contamination usually occurs during unavoidable misuse. Close exposure to an open gas flame, dipping the
sensor in a hydrocarbon such as lacquer, or continuous exposure to heavy concentrations of industrial vapors will
grossly contaminate a sensor. A grossly contaminated sensor causes a continuous alarm.
If a sensor is bad, replace it.
P ROCEDURE :
1. Obtain a new sensor assembly. Make sure the sensor type is identical to your original sensor (019, 030, 812, 813
or 109).
2. Disconnect the orange, brown and blue sensor wires.
3. Unscrew the assembly from the sensor enclosure.
4. Replace the bad sensor and reconnect the wires.
5. Set the sensor heater voltage (See Section 3.4).
6. Recalibrate the instrument (See Section 5.2).
Oxygen Cell
Replace the cell when you can no longer adjust the Oxygen Gain potentiometer to a meter reading of 21%. At this
point, the expired fuel cell will cause the oxygen circuit (channel 2) to be in constant alarm.
1. Obtain a new S-2 oxygen cell, ENMET P/N 67013-008 as furnished as a replacement cell.
2. Remove the four large screws from the top of the cell enclosure.
3. Remove the two smaller screws that hold the cell board to the inside of the box cover (Figure 6). Remove the
circuit board and cell.
4. Unplug the old cell. Pull firmly, do not twist.
N OTE : If your unit is an older model, there may not be a circuit board for the oxygen cell in the sensor enclosure. In
such a case you will have to carefully unsolder the wires from pins on the old cell and resolder the wires to the
new cell (orange to outside pin; green to center pin).
5. Carefully remove the metal shorting clip from the new oxygen cell. Then plug the new cell into the side of the
board with the thermistor and resistor, (enter pin of center hold; see Figure 6.
6. Replace screws to secure the cell in the enclosure cover.
C AUTION : Do not over tighten the screws; over tightening could cause damage to the oxygen cell.
7. Replace the cover.
8. Wait at least four hours for the cell to stabilize. The cell needs to adjust to oxygen, since it has been packaged in
nitrogen.
9. After at least four hours, adjust the Oxygen Gain so the meter reads 20.9%.
10. Verify the alarm point by exhaling over the cell (for about five seconds). The alarm should trigger at the preset
level.
11. If you replace the oxygen cell and cannot adjust it to the proper alarm threshold, open the circuit board enclosure
and check voltages and make potentiometer adjustments as outlined in Section 5.2.2, to recalibrate the oxygen
circuit.