Detective+ Maintenance and Calibration
IX. Maintenance and Calibration
Crowcon recommends monthly gas response checks and a recalibration interval
of 6 months. Flammable sensors will respond to hydrogen and most hydrocar-
bons but will only be calibrated for a specific gas, typically methane.
9.1 Recalibrating
Read about the ‘CALIBRATE?’ option in SETTING UP (CALIB) and the CALIBRATE
functions in Portables PC as either method may be used to adjust gain values,
but a knowledge of both is helpful.
First, remove the pumped flow plate from the instrument, if fitted. Then, zero
the unit in clean air. Place the calibration flow plate over the sensors and secure
with the half-turn fasteners.
Starting with flammable gases and moving on to toxic, connect the appropriate
cylinder of test gas to the inlet of the calibration flow plate. The correct calibra-
tion flow rate is 0.5 litres per minute. Most Crowcon gas bottles use a fixed flow
rate regulator which automatically provides the correct flow rate.
Wait until the reading has stabilised on the Detective+ display before resetting
the reading to the correct level. Now shut off the valve and disconnect the sup-
ply of test gas. Remove the calibration flow plate and allow the sensor to reset
to zero.
9.2 Replacing the Battery Pack
The battery pack should only be replaced by a suitable trained and qualified
Service Engineer. Be careful to retain all nuts, bolts and washers during disas-
sembly. The procedure for replacing the battery pack is as follows.
1) Remove the two security screws on top of the lamp cover on the top
side of the unit, and remove the lamp cover.
2) Remove the centre fixing bolt exposed when the lamp cover is removed.
3) Carefully remove the top half of the unit enclosure, disconnecting the
attached cable at the Main PCB.
4) Remove each cable connection to the Main PCB, making careful note
of where each is attached. Remove the Earth connections from the
stud at the rear of the PCB mounting chassis plate.
5) Remove the four retaining screws from the Main PCB mounting chassis
plate where it is secured to the lower half of the casing on either side.
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