Why does calibration matter? If the equipment has a current calibration certificate and calibration sticker then we can check that off and we are on our way. Well maybe? Too often we overlook a key component for a successful qualification. Proper calibration starts with the manufacturer’s design and operation of the equipment. We purchase equipment for GMP use and fast track the qualification to meet the project deadline. The service manual usually provides a calibration method based on the design and operation of the equipment. In our expedience we sometimes neglect details that we may consider mundane and jump right to our one size fits all method of calibration for related equipment, calibrate and assume success.
Let’s first understand that if equipment passes calibration it only proves that it maintained its calibrated state since the last calibration. It does not guarantee the next day that it is still in calibration. So, calibrating prior to qualification may be beneficial.
Several years ago I was calibrating three new GMP Freezers for a client prior to qualifying them. Our calibration SOP stated to place the calibration temperature test probe in the center of the chamber or adjacent to the controlling probe of the unit, as prescribed by the manufacturer. The service manual clearly stated that the unit be calibrated to the center of the chamber. It just so happened that the client had their calibration contractor performing “6 month” calibrations on the existing identical freezers in the lab. I curiously asked the technician where in the chamber he was placing the calibration temperature test probe. His answer was that they always place the test probe adjacent to the unit’s controlling probe. The controlling probe for these freezers were located in the back right hand side corner of the middle shelf. This location also happens to be the coldest point in the unit. With a quick demonstration the client was able to see that there was almost a 2° C difference in the recorded temperature in the center of the chamber versus the temperature reading with the calibration temperature test probe placed adjacent to the controlling probe. The client’s SOP stated to place the calibration temperature test probe adjacent to the controlling probe of the unit and directed that the three new units be calibrated as such due to the project time constraint and not being able to revise the calibration SOP in time. Our demonstration proved almost a 2° C difference and by calibrating to the coldest point in the unit would jeopardize the acceptance criteria temperature span on the warm side. The first two brand new freezers failed qualification and could not maintain temperature criteria. The warmest locations in the freezer were more than 10° C less than the required set-point. The devastated client quickly revised their calibration SOP and re-calibrated to the center of the chamber with all three new freezers then able to pass qualification.
It is always beneficial to double-check an equipment manual when performing a calibration, even is there is an established procedure in place and you are familiar and comfortable with a certain process. SOPs are often written based on previous practices and may not take new equipment models and locations of sensors into consideration. Verifying the proper set of instructions insures the proper calibration the first time and in the long run will save time and frustration.
Written By: Jim Scearbo, Senior Consultant
ICQ Consultants, Corp.