Differential pressure transducer calibration1

Differential pressure transmitter is widely applied to industrial production, in order to guarantee the normal operation and accuracy, regular check, calibration is necessary.

we know that in the application of differential pressure transmitter is connected to guide pressure tube, usually, need to press guide tube joint apart and differential pressure transmitter, then connected to the pressure source for calibration. This is very troublesome, and the work and the intensity of labor is big, the most concerned about dismantling joint when pressed guide tube pull off or leak problem. Today does not need to be removed is to introduce a guide pipe can be field calibration method.

calibration of conventional differential pressure transmitter

damping adjustable to zero state, first to the zero point, and then filled with pressure adjustable full scale, make the output to 20 ma, calibration on site is fast, the zero point, fast calibration method of range. Tone has no effect on full almost zero, but the full, influential to zero when without migration its influence is about 1/5 the amount of range adjustment, namely range adjusted upward 1 ma, zero point will move up about 02 ma, and vice versa. For example: input full range pressure is 100 kpa, 19900 ma, adjustable range potentiometer output for 19900 + ( 20000 - 19900). ×125=20025mA。 125 = 0025. The zero potentiometer output of 20000 ma. Zero and full range adjustment is normal, then check the middle scale, to see if the error? When it is necessary for fine-tuning. And then migrated, linear and damping adjustment work.

smart differential pressure transmitter calibration

with the conventional method for calibration of intelligent transducer is no good, because this is determined by the HART transmitter structure theory. Because smart transducer in the input pressure source and produce 4 - Between 20 ma current signal, in addition to the machinery, circuit, and microprocessor chip operation work of the input data. So calibration with conventional method.

there are instructions for smart transducer calibration is actually manufacturer, such as ABB transmitter, the calibration is: 'setting range', 'reset range' and 'fine-tuning'. Which set the 'range' operation is mainly through the LRV, URV digital setting work to complete the configuration, while 'reset range' operating requirements connect the transmitter to standard pressure source, through a series of instructions to guide, induced directly by the transmitter of the actual pressure and the numeric set. Initial, final and range of the set is determined directly by the pressure of real input values. But to see despite transducer used in the analog output and input value relations correctly, but the process value of digital readout value will be slightly different, this item can be fine-tuning for calibration. Do a 4 - first 20 ma fine-tuning, the rectification of transmitter internal DA converter, because it does not involve the sensing component, without external pressure signal source. Do it again the fine-tuning, 4 - 20 ma, digital readout in conformity with the actual pressure signal, so you need to pressure signal source. Finally do reset range, 4 - through adjusting the analog output 20 ma in conformity with the additional pressure source, its role and zero (transmitter enclosure Z) , the tuning range ( R) The effect of switch is exactly the same.

discussion: some people believe that as long as the operator can change with HART hands intelligent transmitter range, and can be adjusted to zero and range of work, without the need to input pressure source, but it cannot be called a calibration, can only be called a set the 'range'.

the real calibration is need to use a standard pressure source input transducer. Because do not use the standard and the tuning range ( LRV、URV) Not calibration, ignore the input part ( Input pressure transmitter) To adjust the output ( Conversion transmitter circuit) Calibration is not correct. Moreover pressure, differential pressure detection components and AD conversion circuit, the relationship between the output current is not equal, the purpose of calibration is to find the relation of the three.

emphasize: only on the input and output ( Input pressure transmitter, the AD conversion circuit, the loop current output circuit) Debugging together, just is a real sense of calibration.