Low pressure and differential pressure instrument calibration

Low differential pressure calibration involves verifying the accuracy of instruments that measure very small pressure differences, typically in the 0 to 9,000 Pa range. This range requires specialist reference equipment capable of generating stable, precise low pressures. UKAS accreditation at the low pressure range means the laboratory has been independently assessed for the specific reference equipment and methods used at these pressures, not just for higher-pressure calibration.

At pressures below a few hundred pascals, even small changes in temperature, air currents and the height of the connection tubing can introduce significant errors. Specialist reference equipment — typically precision micromanometers or inclined tube manometers with temperature compensation — is required. Relatively few UKAS laboratories hold accreditation at the lower end of the pressure range, making specialist providers like Labcal an important resource for HVAC and cleanroom applications.

The most common users are quality managers and facilities teams in pharmaceutical cleanrooms, where the positive or negative pressure differential between rooms is a critical GMP parameter. HVAC engineers commissioning and verifying ventilation systems also regularly need low-pressure calibration, as do asbestos surveyors using pressure differential equipment in controlled dismantling environments. Fume cupboard face velocity and containment testing also relies on low differential pressure measurement.

In pharmaceutical cleanrooms, pressure differential instruments are typically calibrated annually as part of the facility’s calibration programme, with more frequent checks as part of the environmental monitoring system. HVAC instruments used in commissioning are usually calibrated before each major project. The calibration interval should be defined by your quality management system and reflect the criticality of the measurement in your specific application.

Gauge pressure is measured relative to atmospheric pressure — the most common type for process pressure gauges. Differential pressure measures the difference between two pressures, neither of which is necessarily atmospheric. Low differential pressure calibration is specifically for instruments measuring small pressure differences, such as the pressure drop across a filter or the pressure differential between two cleanroom grades. Both types are within Labcal’s UKAS accreditation scope.