Magnehelic Differential Pressure Guage Calibration

Magnehelic Differential Pressure Guage Calibration

The Magnehelic® differential pressure gauge is the industry standard to measure fan and blower pressures, fluid and gas air velocity, air filter resistance, furnace draft, the pressure drop across orifice plates, and pressures in fluid systems. It can also check automatic valves’ performance, gas-air ratio controls, and respiratory air pressures in medical equipment.

Manufactured by Dwyer Instruments Limited under its brand name, the Magnehelic differential pressure gauge measures positive, negative, or differential pressures. It has a large dial that provides quick measurements, that are accurate within 4% of full scale.

This gauge is commonly used in chemical processing, power plants, oil refineries, food production, hospital environment, pharmaceutical manufacturing, and industrial processes. It assists with flow measurement and filtration system monitoring. It is often used in biosafety ventilation systems to ensure that appropriate negative pressure conditions are being maintained.



The Magnehelic gauge has a very sensitive diaphragm that responds to changes in pressure. When pressure is exerted on the diaphragm, the dial of the Magnehelic gauge responds accordingly and indicates the appropriate pressure. For this diaphragm to function correctly, it is important to position the instrument in a vertical position. If the Magnehelic is not in a level position, then the diaphragm may sag and give incorrect readings.



The main purpose of calibration is to ensure that the measuring device is giving accurate results. Putting it simply, calibration is the process of adjusting a device to satisfy its manufacturer’s specifications.

Calibration is performed by comparing the output of the under test equipment to standard equipment having known measurement characteristics. Once this relationship with the standard gauge is established, the under test gauge can be certified to be accurate and can be used to measure the pressure of other equipment or systems.

A Magnehelic pressure gauge is usually calibrated by using a standard pneumatic calibrator or a deadweight tester.



Virtually all equipment degrades in some way over time, as some wear and takes place continuously. As a device ages, it loses stability and drifts from its specifications. Even normal use can adversely affect calibration over time, and abnormal usage may lead to a device go completely out of calibration quickly even though it may appear physically undamaged.

Calibration assures that the equipment meets the required specifications. Calibration is required after any maintenance to ensure that the equipment still conforms to the required accuracy. Any organization must have a proper calibration program so that all its equipment functions accurately which leads to quality, efficiency, and thereby increased revenue.



  • Verify that the standard calibrator unit has been currently calibrated following the manufacturer’s specifications.
  • Note and record the temperature and humidity parameters.
  • Clean the test gauge which is to be calibrated and physically inspect it for any damage and physical deterioration. If there is damage then the unit should be repaired first.
  • Select the appropriate standard gauge for calibration.
  • Keep the standard gauge and the test gauge at the ambient conditions for at least 15 minutes or as recommended by the manufacturer, to ensure that both units are stabilized.
  • Connect the high-pressure port of the standard gauge and the test gauge to the corresponding ports of the calibration equipment by using appropriate fittings.
  • Maintain the low-pressure port of the standard gauge and test gauge at some arbitrary constant pressure to avoid the effect due to change in ambient pressure conditions.
  • Ensure that there is no leakage in the calibration system i.e., the low-pressure pump, the standard gauge, and the test gauge.
  • Check and confirm the zero setting of the standard gauge. Adjust pointer.
  • Apply full-scale pressure on the test gauge to check its readings at full-scale. In the case of vacuum range operation, check by applying a full-scale vacuum. Adjust pointer, if necessary.
  • Observe the indicator for confirmation of the smooth functioning of the test gauge.
  • Divide the scale of the test gauge into a minimum of 4 points or as per the client’s specifications.
  • Apply the desired pressure to the standard gauge and the test gauge in ascending order and then in the descending order at the same points. Adjust pointer if necessary.
  • At every point, lightly tap the test gauge, if it is an analog gauge.
  • Compare the desired set readings on the test gauge with that of the standard gauge & record the readings on the calibration data sheet only after attaining the pressure stability.
  • If the measured readings do not match within the specified accuracy of the test gauge, then repeat the calibration steps as mentioned above.



The manufacturer performs the calibration after the equipment is manufactured and tested. Subsequent calibrations are the responsibility of the end-users. They can do this in-house or use a specialized calibration service such as e2b calibration to perform calibration of your equipment. The frequency of recalibration varies depending on the equipment and its usage. Normally manufacturers recommend recalibration frequency but generally, it should be performed once a year. In critical applications, this frequency may be higher.

e2b calibration provides reliable and cost-effective calibration services for Magnehaulic Gauges. Our verifiable and traceable services are unmatched in the industry. We are ISO-17025: 2017 compliant and registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. We are NIST Traceable Wide scope of ISO/IEC 17025 accreditation. e2b calibration can also provide on-site calibration services. Please contact us for more information.


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