Instrumentation Interview Question:

Explain How can a D.P. transmitter be calibrated?

Submitted by: Administrator

D.P. transmitter can be calibrated using following steps:
1. Adjust zero of Xmtrs.
2. Perform static pressure test: Give equal pressure on both sides of transmitter. Zero should not shift either side. If the zero shifts then carry out static alignment.
3. Perform vacuum test: Apply equal vacuum to both the sides. Zero should not shift.
4. Calibration procedure: Give 20 psi air supply to the transmitter and vent L.P. side to atmosphere. Connect output of the instrument to the standard test gauge. Adjust zero. Apply required pressure to the high pressure side and adjust the span. Adjust zero gain if necessary.
Submitted by: Administrator

According to the LRV and URV of DP transmitter,Apply Standard pressure to the HP side of the DP transmitter,and measure the output from transmitter,obviously,in the range 4 to 20 mA ,for the LRV output should be 4 mA an 20mA for the URV,for 4-20mA o/p transmitters.
Apply the standard pressure within LRV and URV of transmitter as 0%,25%,50%,75%,100%,and measure the corresponding output with respect to 4mA,8mA,12mA,16mA,20mA.
LRV=Lower range value
URV=Upper range value
Submitted by: Shefeek Salim