Issue: If RTD connection with TT breaks down, the serial communication between FC-101 and UFM is also breaking down.
Background: The Pressure transmitter PT & Temperature transmitter TT are connected using HART links to Flow Computer FC-101 and RTD is connected by means of three wire to TT. The Flow computer reads flow values from the ultrasonic Flow meter (UFM) using the RS485 MODBUS link. It also writes the line pressure and temperature values from its registers to the UFM registers. This is required to carry out meter body corrections by calculating young’s modulus and to correct the flow by UFM.
Reason: When the RTD is disconnected from TT, the temperature value calculated by TT is a huge value (what is displayed on FC is of order 108 degrees C.) This huge value when written to UFM causes some kind of overflow and the communication between FC & UFM is dropped with error “SICK LINK”, RX fail.
Therefore, if there is any loose contact in RTD terminals, the flow can keep going to zero intermittently with same SICK link alarms and in normal course, the focus would be on flow computer and UFM for such link issues and this RTD angle may not be looked into.
So spare a thought for this issue if any troubleshooting is required in future.