![]() Note that these screws each connect to a variable resistance (potentiometer) and can be turned indefinitely. Locate the manufacturer’s instruction manual and with it locate the transmitters ZERO and SPAN adjustment screws sometimes called Zero and Range adjustment screws. For example, suppose a DP transmitter with output 4 – 20mA is to be used to measure pressure in the range 0 – 300 psig, then the transmitter zero percent ( LRV) is 4mA and will be calibrated to 0psig and the transmitter’s 100%, URV, which is 20mA will be calibrated to 300psig. Note that during the calibration process, the transmitter’s zero percent, ( LRV), is to be calibrated to the, LRV, of the calibration range and the transmitter’s span is to be calibrated to the, URV, of the calibration range. You are now ready to calibrate the DP transmitter. If you calibrate the DP transmitter before first testing and recording the as found data, the history of the device performance data will be lost All the reading obtained will be the as found readings. Continue pressurizing the transmitter and recording your readings for the five points (0%, 25%, 50%, 75% and 100% of input pressure). Record the current reading in (m A) which will be your first data point. ![]() ![]() ![]() So once your equipment is well setup, power it up and pressurize the high port of your DP transmitter. Whether you are doing a bench calibration or a field calibration, the low port of the DP transmitter cell is vented to the atmosphere(as shown in the connection diagram above) and the high port of the DP transmitter connected to a pressure source e.g a hand pump or any other suitable pressure source in a bench calibration or the actual process pressure through a pressure regulator and a pneumatic calibrator in a field calibration. In most calibration done, you will be doing either a bench(shop) calibration – A bench calibration is a procedure where the device is calibrated at a calibration bench using calibration devices to simulate the process, – or a field calibration where the actual process is used. Readings are taken for both increasing and decreasing input values and the corresponding transmitter output values are recorded
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