The Pressure Laboratory, which includes a Vacuum Laboratory, is one of the oldest laboratories at NMISA. In fact, pressure standards were already being established in the late 1950’s. Initially, the driver was the South African Weather Bureau, but later the South African Airways became the main technology driver. Metrological traceability for barometric pressure measurement was a requirement of the international airline association due to its importance in accurate altitude measurement for safety. Pressure is a derived parameter and obtains its metrological traceability from the NMISA Length and Mass Laboratories. 

 

The Pressure Laboratory currently has Calibration and Measurement Capabilities (CMCs) published in the BIPM Key Comparison Database (KCDB) which demonstrate NMISA’s international metrology equivalence. The Pressure Laboratory is also ISO/IEC 17025 accredited from 1,4 kPa to 7 MPa for pneumatic pressure and 0,5 MPa to 500 MPa for hydraulic pressure.

 

The Pressure Laboratory can also perform vacuum calibrations, but these are not yet covered by the current scope of accreditation. The current National Measurement Standard for pressure is a DHI Pressure Balance together with its de​dicated weight stack. See Figure 1 below.

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Figure 1: DHI Pressure Balance with Weight Stack 

 

 
The force is derived from mass and the area is derived from dimensions according to basic formulae (2) and (3): 

Where:F is the force in Newtons (N), m is the applied mass in kilograms (kg) and g is the gravitation acceleration constant in metres per second squared (ms-2)