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One of the pitfalls of not having your vacuum system calibrated regularly is that all electronic
signal converters and amplifiers will tend to drift from their calibrated values over time. Water or steam
from cleaning or sterilisation procedures can also affect the accuracy of measurement. This means that the
actual controlled vacuum is different from the value fed to the control software. Cycle set points may
then be met too quickly, resulting in poorly-dried product; or the set points may take too long to reach,
decreasing overall efficiency and lengthening cycle times. The error may also worsen with time.
GMP and GLP guidelines also require verification of the accuracy of instrumentation.
Calibration of vacuum sensors is a service provided by Biopharma’s technical department.
Vacuum gauges should be calibrated at least annually but every 6 months is not unusual for high
use production machines. The need for calibration depends upon the type of gauge and telemetry
loop fitted, which will vary depending on what freeze dryer you currently have. On small bench-top
and some pilot scale machines, thermocouple vacuum devices are common. Calibration is usually a
simple procedure, utilising a single zero adjustment and perhaps recording the offset across the
working range compared to a known reference.
Other common vacuum gauges used in freeze dryers, particularly larger scale, are the Pirani and
high accuracy capacitance manometer. These devices often require a more sophisticated form of
calibration service where the device in question is tested for accuracy across the operating
range by comparing it with a calibrated reference vacuum gauge.
When we calibrate your freeze dryer's vacuum system we use calibration equipment tested and
maintained to UKAS standards, and a full written report with appendices is provided as standard.
So to maintain the best from your freeze dryer, it is important that you not only keep it
maintained, but you also keep it calibrated!
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