Pressure gauges are commonly found in industries and labs, and their calibration isn’t taken very seriously. But these little devices ensure that everything is going smoothly. They ensure that instruments and machines aren’t over-pressurized. Their accuracy is of utmost importance. Thus, periodic pressure gauge calibration is essential.
Now you must be wondering what the best procedure for it is. Read on to learn how to calibrate a pressure gauge.
What Do You Need for Pressure Gauge Calibration?
- A deadweight tester
- Master Gauge
- And the unit that needs to be calibrated.
The Procedure of Pressure Gauge Calibration
The procedure for calibrating pressure gauges is as follows.
- Check whether the calibrator is correctly calibrated as per the standard specifications.
- Connect your pressure gauge to the device. Ensure that the reading is 0. if it is not. Adjust the pointer.
- Now, apply the maximum pressure that the gauge can handle.
- Release the pressure and see if the pointer goes back to zero. If not, then adjust the pointer.
- Repeat the process several times and adjust the pointer every time it doesn’t come down to zero.
- Now, apply 50% pressure of the maximum pressure. First, check if the meter is reading 50% or not. If not, adjust the scale.
- Repeat the process a few times.
- There are three pressure points on which you must check your pressure gauge- 0, 50%, and 100%.
- Note down the gauge readings.
Factors You Should Consider During Pressure Gauge Calibration
When calibrating a pressure gauge, keep the following factors in mind.
Height Difference
Ensure that both the pressure gauge and the calibration device are on the same level; else, the hydrostatic pressure of the media can cause errors. Keep the gauges in the usual places but find common ground for the calibration device and unit under calibration.
It is not a big deal to use gas as the pressure media. However, if you use oil or water, then gravity will pull at the pressure media inside the tubes, causing errors.
Accuracy Classes
Is every pressure gauge always accurate? Unfortunately, no. A certain margin of error is acceptable. But how to determine it? There is an accuracy class for different pressure gauges, which you must know about before undertaking calibration.
There are different accuracy grades for digital gauges (ASME B40.7) and dial-type gauges (ASME B40.1). Some of them are shown below:
Dial-Type Gauges
| Grade | Permissible Margin |
| A Industrial Gauges | 1%-2% of span |
| B Commercial Gauges | 2%-3% of span |
| C Commercial Gauges | 3%-4% of span |
| D Commercial Gauges | +/- 5% of span |
| 1A Industrial Gauges | +/- 1% of span |
| 2A Process Gauges | +/- 0.25% of span |
| 3A Test Gauges | +/- 0.25% of span |
| 4A Laboratory Precision Test Gauges | +/- 0.1% of span |
Digital Gauges
| Grade | Permissible Margin |
| A Industrial Gauges | +/- 1% of span |
| AR Industrial Gauges | +/- 1% of reading |
| B Commercial Gauges | +/- 2% of span |
| BR Commercial Gauges | +/- 2% of reading |
| 2A Process Gauges | +/- 0.5% of span |
| 2AR Process Gauges | +/- 0.5% of reading |
| 3A Test Gauges | +/- 0.25% of span |
| 3AR Test Gauges | +/- 0.25% of reading |
| 4A Laboratory Precision Test Gauges | +/- 0.1% of span |
| 4AR Laboratory Precision Test Gauges | +/- 0.1% of reading |
| 5A Laboratory Precision Test Gauges | +/- 0.05% of span |
| 5AR Laboratory Precision Test Gauges | +/- 0.05% of reading |
Pressure Media
Pressure media is the matter that is used to gauge pressure. It can be gas or liquid. The choice of pressure media depends on the processes in which the pressure gauge is used.
Adiabatic Effect
The adiabatic effect is the change in temperature of the pressure medium, which influences the pressure and, thus, calibration. The closed environment causes medium, such as gas, to heat up, which increases the pressure. When the gaseous pressure drops, so does the temperature and the pressure, which looks like a leak. But it is the adiabatic effect.
Mounting Position
It is recommended that pressure gauges are calibrated on the same mounting position on which their usual measurements are taken. This is because pressure gauges are mechanical instruments, and their positions can affect the reading.
Contamination
The pressure media you are using should not be contaminated or prone to contamination. Clean the gauges before calibration. Dirt is a major contaminant, commonly present inside the pressure gauges, and can affect calibration.
Leak Testing
Leaks in the pipes can take a toll on the pressure and cause erroneous readings. Thus, leak-test the gauge pipes before starting calibration.
Final Words
Pressure Gauge Calibration is a crucial process that may sound easy in the explanation above, but only professionals can undertake a quality calibration.
If you have pressure gauges at your workplace, you need Biotechnical Service Inc.’s calibration experts to help you. We are proud to be the industry’s most comprehensive equipment calibration service provider. For well-documents, and accurate calibrations, contact us!
