What is calibration?
Comparison of any measured quantity with respect to its standard values is known as calibration.
Span value
The difference between two minimum value and maximum value of readings is known as span value. As shown in fig. below span = 20mA - 4mA
Zero Value
The value of readings at zero line (Y-axis) is known as zero value as shown in figure.
In instrument there are two terms about zero signal,
Live zero :- It means signal coming from field at its lower range value (LRV) means 4mA.
Dead zero :- It means value of actual signal coming from field is 0 i.e, signal is fail to come at controller side.
Comparison of any measured quantity with respect to its standard values is known as calibration.
Span value
The difference between two minimum value and maximum value of readings is known as span value. As shown in fig. below span = 20mA - 4mA
Zero Value
The value of readings at zero line (Y-axis) is known as zero value as shown in figure.
 |
| Fig. showing span and zero adjustment |
In instrument there are two terms about zero signal,
Live zero :- It means signal coming from field at its lower range value (LRV) means 4mA.
Dead zero :- It means value of actual signal coming from field is 0 i.e, signal is fail to come at controller side.
Flow transmitter calibration
If we have to do calibration for flow transmitter we first have to take any transmitter from field, now follow following procedure
1. First give pressure supply (3 to 15 psi) to high pressure side (HP tapping) and low pressure side (LP tapping) leave open to atmospheric pressure.
2. Give +24v power supply to transmitter and connect 250 ohm resistor to +24 v side. Now for getting the signal in form of 4 to 20 mA connect two wires across 250 ohm resistor and connect it to multimeter or hart calibrator as shown in video below.
3. Now give 3 psi signal from compressor to transmitter and note down the reading in multimeter or hart calibrator also check the pressure from compressor side for comparision. Gradually increase the pressure from compressor and note down the appropriate reading in multimeter.
4. After getting all readings, plot the graph of input pressure vs. Output current.
5. If you found the graph characteristics in linear way then its good. Your transmitter is calibrated. But if you found any error please watch following video which will give brief idea of span and zero adjustment.
6.There are two adjustments in transmitter and positioners i.e ZERO and SPAN adjustment. For example, if we calibrate the level transmitter for 4 to 20 mA with the range of 3 psi to 15 psi for 3 psi we must get 4 mA and if it not 4 mA(say 4.6 mA) means, we start to adjust the zero adjustment to make 4 mA for 3 psi And for 15 psi we must get 20 mA and if it not 20 mA (say 19.88 mA) means, we start to adjust the span to 20 mA. This is the way to calibrate the transmitter with the help of zero and span adjustment.
For more information please go through below video :
1. First give pressure supply (3 to 15 psi) to high pressure side (HP tapping) and low pressure side (LP tapping) leave open to atmospheric pressure.
2. Give +24v power supply to transmitter and connect 250 ohm resistor to +24 v side. Now for getting the signal in form of 4 to 20 mA connect two wires across 250 ohm resistor and connect it to multimeter or hart calibrator as shown in video below.
3. Now give 3 psi signal from compressor to transmitter and note down the reading in multimeter or hart calibrator also check the pressure from compressor side for comparision. Gradually increase the pressure from compressor and note down the appropriate reading in multimeter.
4. After getting all readings, plot the graph of input pressure vs. Output current.
5. If you found the graph characteristics in linear way then its good. Your transmitter is calibrated. But if you found any error please watch following video which will give brief idea of span and zero adjustment.
6.There are two adjustments in transmitter and positioners i.e ZERO and SPAN adjustment. For example, if we calibrate the level transmitter for 4 to 20 mA with the range of 3 psi to 15 psi for 3 psi we must get 4 mA and if it not 4 mA(say 4.6 mA) means, we start to adjust the zero adjustment to make 4 mA for 3 psi And for 15 psi we must get 20 mA and if it not 20 mA (say 19.88 mA) means, we start to adjust the span to 20 mA. This is the way to calibrate the transmitter with the help of zero and span adjustment.
For more information please go through below video :
Also refer following link
2 comments
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ReplyThanks, Busarakham.
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