Calibration in field
Most flow meters are sensitive to their working conditions, installation and liquid type. It is therefore quite often that the TOTAL uncertainty gains from a field calibration, even if the field calibration method has an accuracy that is not as good as in a lab. Another important benefit with field calibration is that process disturbances and production stops can be minimized.A field calibration of a flow meter is equal to a calibration with correct liquid, correct flow profile, correct signal converters and no risk for transportation problems. But a field calibration is at the same time equal to the need of a good reference and a lot of know-how. SP s use a number of different methods and equipment wiht different working principles to match the need as good as possible. For precision metering, like in custody transfer applications, we have a number of compact provers with an uncertainty of less than 0,1%
Provers
A compact prover is basically a cylinder with a known volume. During a flow calibration, this cylinder is mounted in series with the flow meter under test. By measuring the speed of a shaft introduced in the cylinder, the true flow rate can be measured (and compared to the signal from the flow meter). Our largest prover, mounted on a truck, can measure up to 26 000 l/min. Beside many types of liquids (up to 120 degC) our provers also work with LPG.
Three different coonnection spots, by a valve-arrangement (1), spoolpiece (2) or at ship-side (3).
Beside a flow connection, also electrical power and a signal connection is needed on site. All instrumentation on-board is Ex-proof. In addition, a sump for draining must be available.
Weighing
For meters that are not very large, we have portable weighing tanks that can be used for flow meter calibrations. The flow is then simply re-routed to the tank, placed on a high accuracy balance. Under good conditions, this calibration method will allow for a very small uncertainty.
Master meters
Another field calibration method is to use an appropriate, calibrated and "good" flow meter - a master meter. This is often more convenient and easier than to use a prover, and can sometimes offer an uncertainty almost as good. We have access to a large number of master meters for different applications, liquids and sizes. All with a frequent calibration "history" and reliable function. Our range of meters include those for use in heavy oils, high temperatures and corrosive chemicals.