Have you encountered a pressure gauge with two entry ports where pressure can be applied?
In this post I will discuss what is a differential pressure gauge, where it is being used and how to calibrate specifically a Dwyer Magnehelic gauge by using a Fluke 754 process calibrator with pressure module.
What is a Differential Pressure Gauge?
There are many types of pressure gauges and Differential pressure gauge are one of them. A differential pressure gauge is a pressure gauge that measures two pressure sources simultaneously in one pressure indicator. But the pressure indicated or displayed is the difference of two pressures, the high and the low pressures.
A differential pressure indicator or gauge is also called DP or Delta P (∆p)
How to calculate differential pressure?
Differential pressure measurement is simply the difference of two applied pressure. One port will result to a negative reading while the other positive.
For example P1 = 100 psi and P2 = 40 psi
So DP = P1-P2 = 100-40 = 60 psi
Most of the differential pressure gauge that I encounter measures a very low pressure value having units in mmH20, mmWC, mmHg and Pa. For this reason, it is also called a differential pressure manometer
Some Applications of Differential Pressure Gauge
- Clean room pressure monitoring – the gauge is installed above the entrance or door. Just in case you cannot remove the differential pressure gauge, you can calibrate it onsite or on its location by opening the door and exposed both ports to ambient before making a measurement. The input ports with a hose are located at the back and front of the gauge, so opening the door will equalize the ambient pressure and the Magnehelic gauge will turn back to zero and it is now ready for calibration.
- Filter in a hood monitoring – installed in hoods or vents
- Use to measure the level of a liquid in a tank or closed vessel
- Monitor pressure in a pass-box
- Filter monitoring in other processes ( usually in pharmaceutical industry)
You may check this link for more detailed applications.
Calibration Setup of a differential pressure gauge ( Dwyer Magnehelic Gauge)
In this post, I will present to the calibration setup for a Dwyer Magnehelic differential pressure gauge. But the principle is the same and can be applied to all including a differential pressure transmitter, the only difference is the output which is digitally displayed and the applied pressure is converted to an electrical signal (4-20ma) going to a PLC.
Connect the output pressure of the pneumatic pump on the positive or high side of the Magnehelic Gauge. Leave the low side or port open to ambient, in this way, the differential pressure gauge functions only as a normal pressure gauge and we can verify one port only with the positive pressure coming from the pump. In this setup, the procedure of calibration is the same with the normal pressure gauge.
This type of pressure gauge should be calibrated using a pneumatic pressure source or pump where-in the fluid used to create pressure is a gas or air. This is to protect most of the differential gauge from possible contamination or blockage since it only requires a small amount of pressure.
Differential Pressure Gauge Calibration Procedure
The reading of the pressure generated by Fluke 754 with pressure module is directly compared to the display or reading of the differential pressure gauge.
- Check for functionality and any visual defect before calibration.
- Record all details about the UUC. Use a Measurement Data Sheet to record your data.
- Open both ports and exposed to ambient. The needle should be in the zero position because no pressure is applied on both ports.
- Connect the pneumatic hose on the positive or high side.
- Then generate the required pressure. Record increasing and decreasing value. Compare reading displayed in Fluke 754.
- Complete necessary record.
- Visit this page to continue data recording—-pressure gauge calibration.
The records and reference standard used in calibrating a differential pressure gauge are the same with an ordinary pressure gauge, the only difference is the setup ( 2 ports), the range of set points and accuracy of the reference standard to be used.
Check this link to see the complete calibration procedure in my older post pressure gauge calibration.
Click this link to check in AMAZON magnehelic gauge.
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