I soon found out that this analyzer could be calibrated in the field using calibration gas and factory instructions! Later, I decided to offer this field calibration service to my customers.
As my customers and students know, most instrument manufacturers thought no one was harder on their combustion analyzers than me. Every analyzer I used was exposed to levels of CO most would never encounter intentionally or not intentionally. Manufacturers believed such treatment would ruin the sensor. That never happened.
So how often was my analyzer out of calibration? How often were the hundreds of analyzers I checked out of calibration?
In some cases, the instruments I checked hadn’t been inspected or calibrated in four or five years. Most were less than 5% off the calibration gas, which was within the manufacturers’ specifications. The only one I found worse than that was a brand-new analyzer just back from factory calibration and it was off by more than 20%!
Even that shouldn’t keep anyone from diagnosing any CO problem.
The Real Problem
CO sensor calibration never misses or overlooks problems.
If the calibration or accuracy of the CO sensor is 100% but you only test a furnace in a home with a water heater and a furnace, the accuracy is only 50%. What if there is a furnace, water heater, and gas range and you only test the furnace? Your accuracy (calibration) is 33%.
If there is a furnace, water heater, gas range, and a gas log and you only test the furnace, your accuracy (calibration) is 25%. By the way, if you only look at one CO reading after five or 10 minutes, your accuracy is off another 50% or more.
And finally, if your analyzer is sitting in your vehicle and you don’t use it, your accuracy is zero.
For years I was told the only reason I found so many CO problems is because I looked for them. Isn’t that our job? If you use your analyzer on a regular basis, you know if it is or isn’t out of calibration.
WARNING: NEVER TURN YOUR ANALYZER PUMP OFF WHEN IT OVER-RANGES ON CO!!
This causes the CO sensor to be saturated and take much longer to recover. Removing your probe from the flue is acceptable but don’t turn the analyzer off. Unfortunately, there are manufacturers that automatically program their pumps to shut down even though they have been advised not to do that.
No matter what — do not turn off the power and try to restart the unit. It will give you error messages for possibly hours. Do not let anyone tell you your CO analyzer is defective. This will not affect the accuracy once the CO clears.
Here’s the Conundrum
Calibration matters, but not as much as how you use your analyzer. A perfectly calibrated instrument sitting in a truck does nothing to protect your customers. The real key to accuracy is thoroughness: checking every potential source of carbon monoxide, not just the obvious ones.
In my decades of experience, my advice is to keep your analyzer in good shape, but more importantly, use it everywhere CO can hide. That’s how you truly keep people safe.
Jim Davis’ career began back in 1971 when he went to work for an HVAC contractor before moving on to work for a distributor in 1977. That is where he became involved with selling the first digital combustion analyzers. He went on to develop the first combustion testing protocols and field diagnostics using a digital combustion analyzer. All (100%) of the combustion taught at National Comfort Institute (NCI)is based on hands-on field experience and actual results. Contact him with any questions at ncilink.com/ContactMe.
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