Alert CM3 Calibration Procedure .
General
The adjustments described below are the only adjustments that are possible. All other settings are
software configured and internally set by precision temperature compensated devices. The calibration
procedure is carried out without removing any covers or lids.
Safety Information
It is possible to calibrate the CM-3 externally. There are no user serviceable parts inside the unit.
Removal of the internal plate from the enclosure will expose DANGEROUS VOLTAGES that
may still be present after the removal of the mains supply.
Before removing any covers disconnect the mains supply and allow 30 minutes for all voltages to
decay.
Equipment required
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4
Digital Voltmeter (Calibrated)
Transducer Test Input Lead (This is made up from a 5 Pin 180o Din Plug with a black wire
fitted with a 4mm test plug connected to pin 5 and a red wire fitted with a 4mm test plug
connected to pin 4)
6mm Nylon pipe
Known negative pressure source 0-40 PASCALs
5
Stabilisation and set-up
· Connect the positive Air port to the negative Airport using the length of 6mm nylon Pipe
The calibration should be carried out at an ambient temperature of approximately 20oC. The
CM-3 should be left in an ambient temperature of 20oC for 45 minutes before it is calibrated to
ensure that it is at the correct temperature.
§ Remove the Calibration Void if Broken Label from the facia. This exposes 2 adjustment
potentiometers (These are single turn potentiometers DO NOT FORCE)
§ Connect the Voltmeter to the CM3 using the Transducer Test Input Lead.
CM-3 Calibration Process
§ Observe the voltage on the DVM,
§ Adjust the right hand (Zero) potentiometer to achieve 0V ± 1mV reading on the DVM.
§ Disconnect the 6mm pipe from the positive airport and apply a known negative pressure of
40.0 Pascal’s to the CM3
§ Adjust the left hand (Span) potentiometer until the reading on the DVM = 4.0V.
§ Observe the CM3 Display and test the calibration on all ranges.
4.00V on the digital voltmeter equals 40.0 PASCALS or 4.09mm H2O or 0.161 Inches H2O
§ Test for linearity over the full range from 0 to 40 PASCALS.