Know Your Curves

Know Your Curves-

Calibration That Is...
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Been a while since I've posted since I've been continuing my research into calibration gas stability with our new coating for both aluminum and steel cylinders. Easy to get carried away with this kind of research after having been involved in this field for forty years!

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So you're trying to keep your people safe and you've bought a new hazarardous gas detector or two or three or twelve. No doubt you've got a combustible (LEL) sensor in whatever you bought since you're likely to run into a flammable gas or two. But just what flammable gas

was your monitor calibrated to at the factory? Some instrument companies, such as Industrial Scientific, prefer pentane. Others use methane. And there are those companies that prefer to send out their combustible monitors calibrated to propane. Are they all equal? More important, what's the difference to you?
There's a world of difference is the simple answer.
First, why is it that gas detector manufacturers use different gases to calibrate their combustible sensors at the factory?
Let's start with the basics. When you're buying a portable gas detector with a combustible gas capability, chances are the combustible gas sensor in your unit has no idea what the gas being detected actually is. It responds to any combustible gas.
Surprised?

You mean you actually thought your portable combustible gas detector actually knew the difference between methane and pentane? Well it doesn't. It's technically what's called a dumb sensor. It's not like it can identify separated components by molecular weight.
But when you're called to an indicident site where potentially flammable liquids and/or gases have been released, wouldn't you like to be able to have your portable four-gas detector tell you which gases you were being exposed to? Sure, we all would, but it's not going to happen unless there's a major technology change.

So, knowing this, the portable four gas detector manufacturers have to also realize that neither their customers are not always going to know what type of flammable gases they're going to encounter in the field. Some do. Say you work for a propane delivery company, or are part of the Hazmat response team for a propane company. You're most likely to see propane. But that's not always a given, since propane delivery companies typical have storage depots full of diesel fuels for their trucking fleet. So you see the problem.

Because of this, some detector companies factory calibrate their combustible sensors with methane since this is a likely gas to encounter, and if a sensor is comprised, it will lose the ability to calibrate quicker than it will with the other gases. In other words, by calibrating to methane, so the thinking goes, you'll be able to detect a compromised sensor more quickly. This is a smart idea.

Other companies factory calibrate their portable combustible detectors to pentane so that they will be more sensitive to methane, i.e., they'll go off more quickly. This also has some good points.

Factory calibrating with propane like some portable gas detector companies do has less to recommend it, and is kind of the bottom curve on the good idea chart.

And all combustible gas detectors have cross-sensitivity factors that you need to be aware of- and you should be aware that they're not always accurate. More on that next time.