Calibrating and testing direct-reading portable gas monitors

This material is presented on OSHA’s website as a Safety and Health Information Bulletin [SHIB 09-30-2013]. The content was written by the International Safety Equipment Association (ISEA). We post the article here, and offer commentary in maroon type… The information in this Safety and Health Information Bulletin (SHIB) provides workers and employers guidance on calibrating…

Perm tube tech: Rigorous discussion of “K” value and best way to calculate gas concentration

Time to get seriously techie on perm tube calibration fundamentals… This is a detailed analysis of the so-called “K” constant used with permeation devices, to enable the calculation of the emitted gas concentration.  Over the years, many of our customers—and Interscan’s own technical personnel—have been frustrated by the confusing and inconsistent documentation on this matter…

Atmospheric Pressure Corrections on Interscan Instruments

Atmospheric Pressure Corrections on Interscan Instruments When a gas concentration is measured or reported, we may talk in terms of ppm, but in reality we are measuring the partial pressure of the gas. (Refer to Dalton’s Law of Partial Pressures) Thus, any instrument reading is going to be affected by changes in ambient pressure. It…

Permeation devices

How To Use Permeation Devices (courtesy of VICI Metronics, Inc.) Permeation devices provide an excellent method of producing known gas concentrations in the PPM and PPB level for calibration of analytical instrumentation. The basic requirement of any calibration system used with these devices is to maintain the permeation device at a constant temperature in a…

Surrogate Calibration

The term “surrogate calibration” refers to a practice in instrument calibration whereby a standard different from the entity to be measured is utilized. For example, thermal flowmeters are based on convective heat transfer effects, and can be calibrated at ambient conditions on a specific gas, and then be used at process conditions to make accurate…

I have seen two numbers relating response of Cl 2 in a ClO 2 detector. One is 3.1 to 1 and the other is 10 to 4, both in favor of ClO 2 . What is the relative response of the Interscan ClO 2 detector and can Cl 2 be used to spot calibrate it?

As you may know, surrogate gas calibration for chlorine dioxide is recommended because it is extremely difficult to generate a stable source of ClO2, especially for practical field use. Indeed, the use of chlorine as a surrogate for chlorine dioxide calibration is one of the very few instances whereby Interscan advocates such a method. Pioneering…

Can the detector be calibrated at one concentration to cover the entire range? Since the response is linear, I think the answer is yes. Please confirm. Thanks.

The answer to your question is YES. You are correct in noting that the response of our instruments is linear. More than that, electrochemical voltametric sensors (such as we use) are inherently linear, with no electronic compensation required. However, for optimum accuracy in most applications, it is best to calibrate the instruments at a concentration somewhere…

Calibration Basics

Introduction It is quite unlikely that you will ever use an absolute method for gas detection. Rather, you will employ any one of dozens of “relative” [or “reference,” but not necessarily EPA Reference] methods—that is, methods that produce some output that must be calibrated against a known standard. Then, its display can be directly read…

In Search of Zero

As discussed in the Calibration Basics Knowledge Base article, Interscan’s gas analyzers, and virtually all other direct-reading gas analyzers are not absolute methods. Rather, they employ “relative” [or “reference,” but not necessarily EPA Reference] methods. That is, methods that produce some output that must be calibrated against a known standard. Generally, these units must also…