A flow meter is only as reliable as its calibration! Whether we’re talking about factory calibration before it arrives at your operation, or periodic re-calibration in the field, proper flow meter calibration is necessary for your systems to function properly.
In fact, there are several different methods of meter calibration currently in use. This gives technicians the opportunity to cross-check results, or simply to pick the method which will be most accurate for a given flow meter implementation. These are the methods most commonly seen in the field.
The Three Most Common Flow Meter Calibration Methods
- Master Meter
This is the most basic and straightforward of calibration methods: Use a pre-calibrated master meter which is known to adhere to accepted standards, then compare its results against the meter being calibrated. As long as the meter itself is reliable and has been recently calibrated, this method is often all that’s needed to verify the accuracy of another meter.
The downside is, of course, ensuring the master meter is properly calibrated. Also, the meter must be compatible with the fluid being measured.
- Piston Prover
Piston provers are one of the most common calibration styles. It consists of a piston sealed within a round cylinder with a known internal diameter. Then you send a known quantity of whatever fluid is being monitored. Positive displacement of the piston creates volumetric flow, and the specifics of flow volume and flow rate can be derived mathematically from the piston’s speed.
This is a highly accurate method and often preferred when calibrating ultrasonic and turbine-based flow meters.
Gravimetric flow meter calibration could be more simply called a weight test. In this method, the flow of liquid is briefly diverted onto a set of scales which weigh the water passing through the pipe, and this is done for a specific duration – usually one minute. Once you have the total weight of the liquid flow for that minute, you can simply divide weight by time to get the flow rate. Then this is compared to the flow meter in question.
This can be an accurate test when performed properly, but it’s difficult to implement ad-hoc. Often, systems will be pre-built to allow gravimetric calibration.
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