CALIBRATION
Establish calibration figures with respect to the L.E.L. limit or the T.L.V. limit of the calibration gas
being used.
The following calibration gases are recommended:
Flammable gases - 2.5% methane in air
Toxic gases - T.L.V.
When using this gas ensure adequate ventilation.
If necessary zero each detector channel in clean air (for ambient oxygen monitoring the meter
reading should be adjusted to read 20.8%).
Apply calibration gas to the appropriate head at a flow rate of approximately 1 litre per minute.
When the METER reads a steady value adjust the Calibration Potentiometer to obtain the correct
reading for the calibration gas being used.
Shut off the calibration gas.
CALIBRATION WHEN USING CV TRANSMITTER (4-20mA DEVICE)
Where a sensor CV transmitter has been supplied the setting up procedure as described on page
15 should be followed.
ALARM LEVEL ADJUSTMENT
The alarm level is factory set at the level stated on the instrument test certificate.
To adjust the gas alarm level.
Adjust the Zero Alarm Potentiometer so that the meter indicates the desired alarm level.
Adjust the Alarm Potentiometer until the alarm is initiated. (The Sounder will sound and the
Alarm Lamp will illuminate)
Accept the alarm by pressing the Reset Switch.
Adjust the Zero Potentiometer so that the Meter reads Zero. Reset alarm by pressing the Reset
Switch.
OVERRANGE LEVEL ADJUSTMENT
As for alarm level adjustment procedure.
SENSOR SUPPLY ADJUSTMENTS (CATALYTIC SENSOR)
For ease of setting, measurements are taken across a 1 ohm resistor (located on the alarm card)
which is connected in series with the supply to the detector head. Current required by each type of
sensor is (VQ21-300mA/VQ23DCP-335mA) therefore measuring mV across the 1ohm resistor at
test points TP (see page 12) will provide a mV reading proportional to mA’s supplied. Adjustment
may be carried out using potentiometer 13 (sensor supply adjustment).
Alternatively the sensor voltage may be set at the detector head across terminal P and W (VQ21-
2v/VQ23DCP-2.5v).
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