Gas Detector Question

if the gas detector has a display on it that shows the ppm LEL the following is the procedure. Connect the 50ppm LEL test gas to the gas meter and start to test. If the meter indicates 50 ppm LEL the meter is in calibration. If not at 50 adjust the meter to read 50 ppm LEL. Your meter is now calibrated for the indicated range of the meter. Gas meters are not calibrated with the anticipated LEL level. They are calibrated with a known ppm sample gas and the meter is calibrated to match the LEL of the known concentration calibration gas. This is the standard way of calibrating gas detectors. If the gas meter is a portable multi-gas meter each gas detector part is calibrated to the standard concentration of the test sample for each appropriate gas. A meter such as the MSA 5 gas meter is calibrated with 5 gases, each one with a test sample of a known concentration to a particular level on the meter. As stated, the meter is calibrated with a gas of known concentration to a specified gas level on the meter, not necessarily a gas of a concentration that the user wants to use the meter at.

This is the standard procedure for calibrating most all gas detectors. What sometimes is difficult for some users to understand is when the sample gas is a different gas and different concentration then the gas the meter will be used with. This is quite often done for convenience or stability of the sample gas. It does work. Although this is not identical, but similar, to keeping wintergreen vapors away from many gas meters while being used to test for gasses. The wintergreen vapors causes a false reading. This phenomenon is sometimes used for training purposes when the gas that the meter is set up for is too dangerous to handle or be near without protection. The wintergreen vapors cause the same meter deflection as the real gas. A gas commonly used for ppm LEL meter is Pentane although the meters indicate ppm LEL for Methane.

The directions or user instructions for the use and calibration of the meter should describe how to calibrate the meter. If all else fails, look it up. If even that does not work contact the manufacturer with your questions.

Good Luck, Old Salt

zhedzuka-

Once a meter is calibrated to the calibration point with the calibration gas it is considered to be calibrated throughout the range. If the user wants to actually test his meter at the operating concentration there are two alternatives. Both require contacting the manufacturer and asking them if there is a stock calibration gas at that concentration or an equivalent concentration of a calibration suitable gas source. If this is not available the next steps are both expensive and could take a length of time.

1) If the manufacturer can supply such a gas have them supply it. This will probably cost between 1/4 and 3/4 of the original meter. Take this gas and calibrate the meter with it.

2) If the manufacturer does not supply the calibration gas at the appropriate concentration or equivalent concentration, contact a gas blender (they normally blend gases for the electronic circuit boards manufacturers) and ask them if they could blend a mixture with the 60 ppm concentration. You may have to supply a sample of the concentrate for them to test and blend. They will then blend your mixture of gases, the standard size being a lecture bottle or 14 oz metal container such as used for consumer use of propane. Caution- if you have any other way to test the calibration gas, test it before using as a calibration gas. Make sure the supplier has supplied what you ordered. There are more mistakes made with custom blended gases than there are "stock" concentrations. Next, use the supplied custom blend to calibrate you meter at the concentration desired.

3) Contract with an appropriate meter calibration firm, if one is available. This will probably be the most expensive since they have to recoup the costs as if you did it themselves and then add in labor, overhead and profit.

Either one of these procurement methods will be expensive and require considerable lead time.

If all else fails, contact another user of that type of instrumentation and tested gases and ask them what they do.

If everything completely falls apart post another question on CR4. Caution though, the population you are dealing with might not be what you expected. We are usually engineers, scientists and very knowledgeable people with a lot of knowledge. Some are extremely knowledgeable on several subjects and familiar with several others. From there it goes down to familiar with one subject or less. The "worthless" answerers are the ones you need to ignore. Unfortunately, you are the only person who can decide which are good and which are trash. How would you tell the difference between an extremely expert answer from one that is only posted for the glorification of the author. Likewise some answerers will post a completely error filled answer just to try to make you seem like an ignorant idiot. How do you tell the difference? How do you know that I am not including trash in this answer?

Good Luck, Old Salt