Recently Emerson received a call from a customer stating its GC was not operating properly and requested a highly skilled Emerson service technician be deployed as the customer was convinced it was a GC problem. It took a few days until the technician could get on-site. The technician realized the calibration gas had gone bad within a short period of time being on site. How? The tech followed the Verification Process to determine if the GC is operating properly. Emerson thinks this process is so important that it gives classes on it. Customers state they “run the calibration gas as an unknown” and compare the results to the gas’ certificate to determine if the GC is operating correctly.
Running the calibration gas as an unknown will only confirm that the GC reads what it has been told to read, not whether it’s operating correctly. So what is the Verification Process? It starts with the downloading and checking of Alarm and Event Logs, Final Calibration Report and Calibration Chromatograms and ends with checking for changes that may affect the future reliability of the GC. On the Final Calibration Report, you look at the Calibration Gas concentrations and the Response Factor order. It was this report that clued in the technician to the problem. First the magnitudes of the Response Factors were not in the proper order (smallest to largest: Methane, Nitrogen, Carbon Dioxide, Ethane, Propane, iso-Butane, normal-Butane, neo-Pentane, iso-Pentane, normal-Pentane and C6+). This indicates there is a calibration or a valve-timing error. After adjusting the timing and running a calibration cycle, the magnitudes of the Response Factors were still not in the proper order. The technician then looked at the calibration gas concentrations on the Calibration Report. While the values on the report matched the certificate, the values did not sum up to 100%. This helped to convince the customer it was the calibration gas and not the GC. I could not help but think that if the customer had taken our Verification Process class, he could have found the problem on his own, saving himself time and money.