Calibration procedure for the Monoxor II

First off, do remember, only calibrate the CO sensor of any instrument in a well ventilated area!!!

Carbon monoxide is a toxic gas and while only a small amount of CO is used during the calibration procedure and quickly diluted by the ambient air, it is a toxic gas and exposure to even small amounts in a confined space can potentially ruin your entire day!!

If you are primarily performing flue gas testing, we suggest you calibrate your Monoxor II with 500 ppm calibration gas.  If you are primarily doing ambient testing, you may wish to consider 100 ppm calibration gas.  If you have any questions, please feel free to contact us.

The first step in calibrating the instrument is to turn it on in 'clean air' for a minute or two until the reading stabilizes.  If it is not reading zero, use the 'zero adjust' screw to adjust the display to zero.

If you have trouble getting the instrument to adjust to zero, there is a good chance the sensor has reached the end of its life.

To replace the sensor either send the instrument to an authorized service center or it can be replaced by the customer.  Do keep in mind that when a CO sensor is replaced, it is absolutely necessary to calibrate the sensor.

Set up the calibration kit as described in the manual with the long hose going to the regulator, one of the shorter hoses going to the flow meter and the other to combustion gas intake on the bottom of the instrument.

Tip:  Set the bottom of the flow meter stand under the cylinder of gas to support it.

Once the connections have been made, adjust the regulator on the cal gas cylinder so the flow meter reads approximately 2 SCFH.  The valve on the regulator is turned clockwise to open, counter clockwise to close.

Wait 2 to 3 minutes or until the reading stabilizes (Photo below is using 100 ppm calibration gas).

If the reading in the display does not match the ppm level of the calibration gas, adjust the reading through a hole located on the back of the instrument.

You will need a small straight slot screwdriver to make the adjustment or the 'special' screwdriver from Bacharach.

Below is a photo of the adjustment screw with the instrument case removed and the circuit board exposed - it is small and may require a little patience to locate.

Turn the screw clockwise (from the back of the instrument) to increase the reading in the display, counterclockwise to decrease it.

Adjust the screw until the reading matches the ppm reading on the calibration gas cylinder - 100 ppm in this case..

Once the adjustments have been made and the reading is stable, shut off the regulator on the calibration gas and disconnect the hose running to the top of the instrument.

Leave the instrument running until the display reads zero (plus or minus 3).  If the reading does not return to zero (plus or minus 3 ppm) perform the calibration procedure again.

Note:  When the instrument is turned on again, adjust the 'zero adjust' screw (in fresh air) on the front of the instrument until the display reads '0'.

It is very important to remember that once the zero adjust is set (to within plus or minus 3ppm), there should be no need to continually reset the zero adjust. Continually having to zero the instrument is typically caused by a weak sensor.

Also keep in mind that adjusting the zero in an area with ambient carbon monoxide levels (near a busy street, for example) will result in a 'false' zero.

Go somewhere you know the air is clean, set it and leave it.