DP Flow Transmitter Testing and Recalibration

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In the first video of this 2-part series, we showed you how a Differential Pressure Transmitter is used to measure the flow rate. (https://realpars.com/flow-rate/)

This second part of our series will take you through the process of checking the output accuracy of a differential pressure flow transmitter and show you how to recalibrate it if necessary.

If you haven’t already done so, you might want to review 2 of our other videos:
Differential Pressure Transmitter Explained (https://realpars.com/differential-pre...)
What is Sensor Calibration and Why is it Important? (https://realpars.com/sensor-calibration/)

The transmitter must be removed from service before any checks or calibration can be performed. Let’s go through the following steps:

– Close the Low-Pressure Block Valve
– Open the Equalizing Valve
– Close the High-Pressure Block Valve

The first thing we need is a calibration chart or table.
The table is important from a calibration perspective as it indicates what we need to apply to the transmitter, and what the expected current output will be.

Calibration Setup:
The scissor-type hand pump with a digital pressure readout is connected to the high-pressure side of the transmitter.
There are several different types of pressure sources used in the industry.

Note that the low-pressure side of the transmitter is vented to the atmosphere.
A digital multimeter set to measure current is connected in series with the transmitter and the 24-volt power supply.

First of all, we’re going to check to see if the transmitter needs to be adjusted.
We begin by applying the desired pressure input values from the calibration table to the high input on the flow transmitter and record the output current measured for each input value.

If the output currents measured are outside of the acceptable ranges as established by your company, then the transmitter must be recalibrated using the Zero/Span adjustments.

We perform the actual calibration using the Zero/Span adjustments on the transmitter

Let’s return the transmitter to service now that it’s been calibrated.

– Begin with all valves closed
– Open the equalizing valve
– Open the High-Pressure Block Valve
– Close the equalizing valve
– Open the Low-Pressure Block Valve

Here is a review of what we discussed in the video:

– Before calibration, a transmitter must be removed from service by closing the Low-Pressure Block Valve first, then opening the Equalizing Valve second, and finally closing the High-Pressure Block Valve.

– Checking and calibrating the transmitter is completed by using values found in a Calibration Table or Chart kept onsite. The Zero/Span adjustments are used to obtain a specific current output range for a 0% and a 100% differential pressure input.

– After calibration, a transmitter is returned to service by opening the Equalizing Valve first, then opening the High-Pressure Block Valve second, followed by closing the equalization valve, and finally opening the Low-Pressure Block Valve.

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Missed our most recent videos? Watch them here:

https://realpars.com/flow-rate/

https://realpars.com/wireless-communi...

https://realpars.com/vba/

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