Carbon Monoxide Transmitter Modbus
Installation Manual
May 5, 2017
IN-CMD5B4MOD-01-01 Page 10
Calibration
The CO transmitter features a cover mounted sensor pcb that is pre-calibrated. This means that the entire sensor pcb can
simply be replaced with a new calibrated pcb if desired without having to remove the enclosure and the main processor
board. This sensor swap can be completed in seconds. Simply unplug the device ribbon cable connection, remove the old
sensor pcb, install the new pcb and reconnect the ribbon cable. There is no need to make any adjustments or apply gas to the
transmitter using the sensor swap method.
In this case, the Fault Mode should be reset if it is enabled.
The device may also be calibrated or verified with CO gas if required. This requires a field calibration kit consisting of a
bottle of gas (250 ppm CO in air for example), a tank pressure regulator with flow restrictor and the necessary tubing with a
calibration cap to cover to the sensor. Calibration can be done at 20-27
C.
Verification with gas can be done without removing the device cover. Simply apply gas using the calibration cap attached
directly to the port on the cover and monitor the output signal or LCD.
The device cover must be opened to perform an actual calibration. In this case, the gas calibration cap attaches to the sensor
fixture on the cover as before. The sensor must be continuously powered for at least 1/2 hour prior to calibration. Calibrate
the sensor first in clean air with no CO gas present. Simply adjust the ZERO pot on the sensor board until a 4 mA (or 0 Vdc)
output is obtained and the LCD displays 0 ppm. Note that the "0 Filter" menu item should be disabled to set the 0 ppm. The
ZERO and SPAN pots are located on the edge of the cover sensor pcb and are clearly marked on the pcb.
Then attach the gas supply. Turn the regulator on/off knob fully off and attach it to the 250 ppm gas bottle and firmly tighten
it by hand. Moisten the sponge and squeeze out any excess water. Place the sponge in the cap so that it will not touch the
sensor but does not plug the hole in the side of the cap. Attach the cap to the fixture over the sensor. If the gas cap is too loose
on the fixtures, simply place a wrap of electrical tape around the cap to tighten it up. Slowly turn the valve knob on the
regulator to let the gas begin flowing.
The regulator will restrict the flow rate to the specified 200 ml/min and the sponge will ensure the gas is in the right humidity
range. Wait for 5 minutes and then adjust the SPAN pot on the sensor board until the output and LCD reads 250 ppm. Close
the valve on the tank and take the cap off from the sensor. Calibration is complete.
In this case, the ReCal Mode should be
reset if it is enabled.
