Watch Out When Using A Zero Filter

Especially when doing low range work, it is important to make sure that your instrument is properly zeroed. Ideally, zeroing should be performed with a certified zero gas. However, mostly since it adds another step to the calibration process, this practice has somewhat fallen out of favor. The alternative to a zero gas requires that…

Bump testing

The closest thing to an official definition of “bump test” appears in an OSHA Safety and Health Information Bulletin (SHIB 09-30-2013) entitled “Calibrating and Testing Direct-Reading Portable Gas Monitors.” We have posted a Knowledge Base article providing some commentary on that Bulletin. Here is what the Bulletin says about Bump Testing (DRPGM = Direct Reading…

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…