Loop Testing Procedure for Non-SMART Transmitters

How else would you check loop integrity, regardless of isolated transmitters or not?

There is no difference to the nature of the loop testing procedure done on Smart or Non-smart or FFB transmitters. The non-smart transmitter can be loop tested using pressure calibration equipment to simulate process conditions and verify/confirm the output at the system end. In this way the integrity of the instrument and the loop wiring are checked.

The current simulation is also acceptable, it is a matter of preference and what is specified in the contract since simulating process conditions using pressure calibrators involves increased man-hours and additional equipment.

Yeap, These procedure are correct. In the old days, Loop testing procedure for NON-SMART Transmitters" is the following steps,

1. Disconnect the signal wiring at the transmitter terminal and connect a 4-20 mA signal generator to the signal wire.
2. Simulate 0, 50, 100% signals and confirm the reading at the receiving end.
3. Restore the current wiring to normal after the test.

I have been using this step for last 10 years until we replace it with a Smart Transmitter.

There is no reason why a non-smart transmitter cannot be loop tested using the same method as a smart transmitter i.e. using pressure simulating/calibrating equipment such as hand-pump and test gauges or a druck pressure calibrator.

Another advantage of this is that an ammeter can be placed in series with the transmitter (connected in the field) so that

1. it can be identified if the calibration is off and,

2. calibration adjustments can be made on the spot.

With the smart transmitters this is achieved using the HHT such as HART 375, with the non-smart transmitter the only way of identifying this is using the ammeter to measure the 4-20mA (or to wait until the operator complains).

Again this is a matter of preference and/or what is specified in the contract or by the client/owner/operating company.

All the suggested procedure is doing is checking that when a 0%, 50% and 100% signal goes in at the transmitter end, that a 0%, 50% and 100% signal comes out at the other. If the loop has too much resistance in it, it might be a bit shy at the higher percentages, in which case it needs to be reconfigured either to reduce the loop resistance or increase the loop supply voltage. Of course, this is the purpose of the test.

Nothing here is HART transmitter-specific. In fact, it shouldn't matter whether a HART or a non-HART transmitter is present; the procedure is valid for all 4-20mA current loops.

Just Make sure the loop is open ,

For Closed loops u have to consider the Final Element also

Regards

Jose

Hi there,

Whether we are testing a smart transmitter or not - this is the procedure we follow. I will use a simple pressure transmitter as an example. This procedure verifies the trasmitter calibration as well as the wiring.

1. Disconnect impulse leg from process line.

2. Attach pressure pump to transmitter leg

3. Check zero

4. Use pump to induce pressure

5. Check 50%

6. Check 100%

7. Release pressure slowly

8. Check 50%

9. Check zero.

Depending on your transmitter type - you could have your multi-meter in series and measure the current - and/or talk to your operations personnel monitoring the control system.

Purely using a current source at one end does not verify the transmitter calibration or that the transmitter is working correctly.

The pressure pump we use is a Beamex or something similar.

Regards,

Craig