With over 30 years’ experience, Michell Instruments designs and manufactures a wide range of transmitters, instruments and systems capable of measuring Dew-point, humidity and oxygen in a variety of applications and industries that includes power generation, process, oil and gas and, significantly, compressed air.

 

Its production and calibration processes are critically dependent upon a continuous and reliable supply of quality compressed air and over the past ten years, as the company’s production and calibration facility has expanded, Atlas Copco has matched this growth and production demand with oil-free compressor solutions that offer increased capacity and technical sophistication.

 

Graham Daines, Michell’s calibration laboratory manager, explained: “The compressed air is used to supply the Dew point calibration systems we use. These systems vary in design, but basically perform the same function of mixing varying amounts of moisture into very dry air (-100degC Dew point) to give a range of Dew points from -100 to +90degC. The systems perform Dew points calibrations under our UKAS accreditation and all traceable Dew point calibrations on manufactured instruments and sensors.”

 

The UKAS calibrations are low volume, typically less than 10 units per week, but the production calibration systems are high volume, at the rate of more than 250 units per week. As the number of systems in the production and development departments has increased over the years, and with the latest high volume systems using 100 litres of air per minute, there has been a corresponding need to increase the air supply.

 

Air quality vital to calibration procedures

The most recent addition of an Atlas Copco oil-free ZT22 compressor and two CD dryers, supplied and installed by Peterborough-based Anglian Compressors and Equipment Ltd., underlines the fact that air quality is vital to the calibration procedures. Daines commented: “The calibration systems use pressure swing dryers to achieve the -100degC Dew point air and require the air supplying them to be dry and oil free. We cannot risk contaminating the calibration systems or the sensors we calibrate. This is why we have never considered oil lubricated compressors with oil filtration.”

Continuity of supply is equally important, that is why the company has set up a system of compressors and dryers to ensure continuity in the unlikely event of a breakdown or when scheduled equipment servicing is required.

 

Previously there were two existing dryers plus three piston compressors, installed by Anglian Compressors, but this system was upgraded when the company moved from Cambridge to its new Ely factory in 2007. An Atlas Copco SF-15 scroll compressor was installed with one of the existing dryers. This enabled Michell to maintain the calibrations system in Cambridge and transfer the others one at a time to Ely, ensuring that each was fully operational at the site before moving the next one. When the move was complete, the set up comprised the SF-15 with two dryers (one for backup), with the two piston units working together as backup for the SF-15, should it be required.

 

The factory then underwent a substantial expansion programme during 2011 to meet global demand − a 20,000sq.ft extension that would enable the company to double its production output through additional calibration systems.

The air supply was already very close to its limit so, in July 2011, an Atlas Copco ZT-22 oil-free compressor was installed together with two CD70+ dryers (again, one for backup) with the scroll compressor and the two piston units working together as backup for the ZT machine during service periods. Anglian Compressors were able to install the ZT-22 and the Atlas Copco dryers plus all the compressed air system’s pipework without any interruption to the essential air supply.