In pressure calibration, reference modes refer to the methods or standards used as a reference to establish the pressure applied to the instrument being calibrated. The choice of reference mode depends on factors such as accuracy requirements, the range of pressures being calibrated, and the availability of suitable reference standards. Here are the different reference modes commonly used in pressure calibration:

1. Dead Weight Tester (DWT):

   • Dead weight testers use calibrated weights and a piston-cylinder assembly to generate known pressures.
   • The weight of the masses applied to the piston generates a force, which, when divided by the area of the piston, yields the pressure.
   • Dead weight testers are highly accurate and are often used as primary standards for pressure calibration in laboratories.

2. Pressure Comparator:

   • A pressure comparator compares the pressure applied to the instrument under test with a reference pressure generated by a calibrated piston-cylinder assembly or other standard.
   • Pressure comparators can be hydraulic or pneumatic and are suitable for calibrating pressure gauges, transducers, and transmitters.

3. Digital Pressure Calibrator:

   • Digital pressure calibrators use electronic pressure transducers to generate and measure pressure.
   • They are versatile and can be used for a wide range of pressure calibration applications.
   • Digital pressure calibrators may have built-in reference standards or allow for connection to external reference standards.

4. Master Gauges:

   • Master gauges are high-precision pressure gauges calibrated to national or international standards.
   • They are used as reference standards for calibrating other pressure instruments.
   • Master gauges are typically calibrated by accredited calibration laboratories and are traceable to national standards.

5. Pressure Balances:

   • Pressure balances use the principle of force balance to generate and measure pressure.
   • They are often used for high-pressure calibration applications, such as testing safety relief valves and high-pressure transmitters.

6. Digital Multifunction Calibrators:

   • Digital multifunction calibrators are versatile instruments capable of calibrating various parameters, including pressure.
   • They may use internal pressure transducers or allow for connection to external pressure standards for calibration.

7. Pressure Transducers/Transmitters:

   • High-accuracy pressure transducers or transmitters can be used as reference standards for pressure calibration.
   • These instruments are calibrated to traceable standards and can provide accurate and stable pressure references.

The choice of reference mode depends on factors such as the required accuracy, range, and application-specific requirements. Calibration laboratories and facilities may use a combination of reference modes to cover a wide range of pressure calibration needs. It's essential to ensure that reference standards are properly maintained, calibrated, and traceable to national or international standards for reliable pressure calibration.