We have 05 Vortex Flow Transmitters of make Rosemount and model 8800D installed for fuel gas metering of Gas Engines.

Recently, we tried to calibrate these transmitters with HART-375 field communicator and found that 03 of these transmitters were unable to communicate with HART-375. We have all the updated Device Descriptions of the relevant transmitters in HART-375, and that's why it was able to communicate successfully with the remaining 02 transmitters.

The 03 non-communicating transmitters are displaying the process value normally and no Error Code is being displayed on the LCD of these transmitters.

What could be the possible cause of communication problem in these transmitters? If anyone has experienced such problem please share it.

 

Things to check out:
1) Some wise guy assigned some HART address other than zero to the three devices that don't communicate.

2) The three uncommunicative meters are connected to an analog input whose input resistance is less than 230 ohms. Add some loop resistance.

3) Insufficient loop voltage - the bare minimum needed to run the transmitter, might not run HART.

page 28: "A minimum loop resistance of 250 ohms is required to exchange information with a HART-based communicator. With 250 ohms of loop resistance, the flowmeter will require a minimum power supply voltage (Vps) of 16.8 volts to output 24 mA.)"

4) The three uncommunicative units are subject to a high electrical noise level that interferes with the HART signal.

5) You're connected at a point in the loop where the HART signal is stripped off by a loop powered meter, isolator, splitter, or some other device with typical 4-20mA low pass filtering.

The 8800D manual offers this troubleshooting advice:

- Check for a minimum of 10.8 Vdc at transmitter terminals.
(minimum voltage level contradicted by the separate note on page 28 (above)

- Measure loop resistor value (Rloop) and source power supply voltage (Vps). Check that [Vps - (Rloop x 0.024)] > 10.8 Vdc.

- Check for transmitter in multidrop mode.

- Check for transmitter in burst mode.

- Remove pulse connection if you have a three wire pulse installation (infers an electrical noise situation).

 

Thanks David !!

We have checked the following:

1- Used multi-drop and burst mode for HART communication but not successful.

2- Have added a loop resistance of 250 ohms in series with the supply voltage but no success.

3- Checked our loop voltage which is 24Vdc. Moreover, we also have provided independent supply of 24Vdc to one of the transmitters in our workshop away from the field. Still not successful.

4- As far as high noise interference is concerned, we have checked one transmitters in Workshop using an independent noise-free DC power supply but still no communication.

We even sent one transmitter to our local supplier/vendor and he suggested that there seems to be a problem with the electronics. However the unit is displaying no Error code and is showing real-time process value correctly. So, electronics seems healthy.

Still unable to locate the fault.