Checking the CDR/SRC100/SRC200/TER/RHR Communication Channel
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Checking the CDR/SRC100/SRC200/TER/RHR Communication Channel

Author Jukka H...
Moderator
#1 | Posted: 15 Oct 2018 13:30 | Edited by: Jukka Hurtta  
On occasions we get reports on the CDR/SRC100/SRC200/TER/RHR that communications does not work to the Modbus master / BACnet MS/TP client. Typically the communication issues are resolved by:-
- using correct communication cable (twisted pair with shield)
- linking all devices to the same potential using G0 terminals
- making sure that devices are powered from 'floating' power supplies to make sure that ground loops are not present

On occasions the communication electronics on the above devices are damaged by incorrect wiring (e.g. connecting 24Vac to the communications ports), or after installation high voltage peaks are induced to the comms cable (e.g. because of lightning).

The quick and easy way to check the physical communication channel on the electronics is by measuring resistance using multimeter:

The procedure is as follows:
- Remove power from the device
- Remove any cables from A+, B- and G0 terminals

Measure resistance between terminals
A+ and B-
A+ and G0
B- and G0

All should be around 250-310kOhms

If the resistance is massively different e.g. mega Ohms, then the communication channel is damaged. On occasions the communication channel can be repaired, please contact SyxthSense Team for further details.
Author Jukka H...
Moderator
#2 | Posted: 31 May 2019 08:51  
Further checks that can be done is by removing the PCB (electronics board) from the plastics enclosure, and then measuring the resistance on resistors R10 & R11 on the back of the unit (bottom right). No wires connected. These should be about 22 Ohms. If they are substantially different the devices have been damaged.
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