Calibration in the Cleanroom
The importance of particle counting, testing of HEPA filters, etc. is widely known, but how important is the calibration of the associated instrumentation within a cleanroom environment?
One of the most prevalent devices in a cleanroom environment is the Magnehelic gauge. These are used as an easy to read indicator for operators to confirm that the differential pressure between two rooms is as it should be, they are often used in conjunction with an alarm monitoring system. The question is, have yours been calibrated correctly though? In our experience gauges like this are checked and perhaps adjusted at 0Pa but that’s it. Magnehelic gauges are known to be very accurate; however they still require more than a zero point calibration check. A full 5 point, rising and falling test is the most thorough calibration that can performed with these and many other pressure gauges.
UKAS Calibration companies are able to provided the knowledge and training to perform complete calibrations of any instrumentation within a cleanroom. This ensures that customers receive a complete package of cleanroom testing and validation as well as calibration.
Refering closely to the “Orange Guide” (The MHRA Rules and Guidance for Pharmaceutical Manufacturers and Distributors 2007) which states the following with regard to calibration, Equipment Section 3.14
“Measuring, weighing, recording and control equipment should be calibrated and checked at defined intervals by appropriate methods. Adequate records of such tests should be maintained.”
The guide states the above for good reasons, some of which are identified below.
Differential pressure switch calibration
One example of a situation encountered by our engineers was in a plant room at a pharmaceutical site. The differential pressure switch across a bag filter had been set to alarm to the BMS at 240Pa to flag up the need to change the filter. However when our engineers calibrated this switch we found it to be switching at just 80Pa! The BMS interface was therefore prematurely flagging up this filter as being blocked. Discussions with the customer found that the particular filter in question had been changed more often than others. Thanks to our findings the faulty pressure switch was changed thus saving the customer any further unnecessary filter replacements, not to mention time and money.
AHU sensor calibration
Another area where calibration can aid in energy and money saving is within the Air Handling Units themselves. Correct calibration of temperature and relative humidity probes that control the heating, cooling, humidifying and dehumidifying can save energy. The outputs of the sensors control the amount of heating and cooling that is called for via the BMS and conflicting sensor outputs at various stages of the AHU can result in wasted energy from steam heating the air and chillers running unnecessarily to cool air. We have witnessed on several occasions systems that are both heating AND cooling at the same time.
Furthermore, sensor outputs must correspond with the condition that the sensor is measuring otherwise the error will be passed onto the BMS which will produce further errors. A situation could arise from this where your BMS system says that a room is being controlled at 21°C and your EMS says that the room is at 23°C. Offsets created by the calibration of the BMS sensors can eradicate these discrepancies to allow the system to be more easily manageable, more accurate and more reliable as an information source.
The most important instrumentation within a cleanroom is the environmental monitoring system (EMS). This should be a CFR21 Part 11 logging system monitoring several aspects of the room such as temperature, relative humidity, and the pressure between rooms. It is crucial that these are calibrated properly to help maintain regulatory compliance. This calibration ideally should be performed during a plant shutdown due to the amount of access required by the engineers and the disruption caused to the EMS system. To reduce confusion and any discrepancies, indicators and gauges within the cleanroom such as the aforementioned Magnehelic gauges should be calibrated to the same method as the EMS sensors.
In conclusion it has to be said that calibration of instrumentation in cleanrooms is very important from the logging system of the EMS to the air handling units supplying the air to the room. Each part of the system plays vital role in the efficient operation of a cleanroom.
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