ENMET ISA-44-RALE-OD - Manual (Page 32)

ENMET Corporation ISA-44RALE-OD/ISA-44RAHE-OD/ISA-44E-OD
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7.5 Sensor Heater Voltage
Heating the sensor promotes the oxidation reaction on the sensor element surface. The temperature to which the sensor
element is heated determines the selectivity of the equipment to certain gases.
The heater voltage is specified and labeled on the display plate of the instrument. Channels with PURGE switches have
two voltages specified; one is for heater voltage, one is for PURGE voltage.
N OTE : Do not increase any sensor voltage to values greater than those given on the unit. Too high voltage can damage the
sensor heater winding, making sensor replacement necessary.
If the sensor is located 10 feet or more from the control unit, you must initially measure the sensor voltage specified in
this procedure across the brown and orange wires inside the sensor assembly. Once the voltage has been set correctly at
the sensor, then measure the corresponding voltage across the heater (positive; red) and ground (negative; black) test
points on the display plate of the unit. Record this voltage. Now whenever the sensor voltage must be corrected, all you
need to do is adjust the voltage so that you gain your recorded voltage across these test points. If the sensor assembly is
closer than 10 feet from the unit, simply measure the sensor voltage specified in this procedure across the heater and
ground test points on the display plate of the unit.
MATERIALS:
q
voltmeter with + or - 0.05% accuracy (digital is best)
q
small screwdriver
PROCEDURE : Instruments with PURGE Switch
1. With PURGE switch on, adjust the purge adjust pot. (R38...see Fig. 7) to the purge voltage specified on the enclosure.
2. Turn the PURGE switch off.
3. Now adjust the heater adjust potentiometer (R32) to the specified voltage.
PROCEDURE : Instruments without PURGE Switch
1. Adjust the heater adjust potentiometer (R32) 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. (R38) to arrive at the necessary
voltage.
7.6 Sensor Assembly Replacement
Replace the sensor assembly if either of the following conditions occur.
♦
Fault Condition: The red fault LED indicates a fault in sensor continuity. Either the sensor is bad and needs to be
replaced, or there is an open wire somewhere between the sensor assembly and the control unit.
♦
Gross Sensor Contamination: Close exposure to an open gas flame, dipping the sensor in lacquer, or continuous
exposure to heavy concentrations of industrial vapors will grossly contaminate a sensor. A grossly contaminated
sensor causes a continuous alarm and the meter to drift slowly upscale.
PROCEDURE : Sensor Replacement
1. Obtain a new sensor assembly. Make sure the sensor type is identical to your original sensor.
2. Disconnect the orange, brown and blue sensor wires.
3. Unscrew the assembly from the sensor enclosure.
4. Replace the bad sensor with the good sensor and reconnect the wires.
5. Set the sensor heater voltage(s).
6. Recalibrate the instrument.
7.7 Hydrocarbon Filter Replacement
The charcoal absorption filter for hydrocarbons will need periodic replacement. The length of time between
replacement depends on the instrument usage and VOC (Volatile Organic Compounds) level in the breathing air supply.
For ISA-RAL monitors that are in continuos air streams, 24 hours, 7 days a week 365 days a year it is recommended
that the filter be replaced when any of these conditions occur:
•
At least annually
•
Any time fluid is found inside the filter
•
Any time the filter is damaged
•
If any odor is detected in the breathing mask