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11.3.6 Troubleshooting
If you are experiencing a communication issue with a Tan Delta sensors following a ModBus
installation, please carefully review the following points;
1) Does whatever monitoring system you are using (Monitoring System) use an RS485, 2 wire,
half duplex serial interface?
2) Does the Monitoring System use Modbus RTU, not ASCII?
3) Is the Monitoring System set to use the correct COM port (that is connected to the sensor)?
4) Is the Monitoring System set to use 9600 baud, 8 bits, 1 stop bit with no parity?
5) Is the Monitoring System trying to communicate with the correct Node ID for the sensor
(Sensor Node ID 0 will be forced to Node ID 1)?
6) Has the sensor been set to Modbus using Tan Delta Configuration & Data Software, or
register 12 (zero based) to 0x03 or 0x13 (decimal 3 or 19) by other means?
7) Has the sensor been powered off and restarted after setting to Modbus?
8) Is the sensor firmware V2.28 or V3.xx? If not, please ask TD for confirmation.
If no response whatsoever is being received….
1) Does the Monitoring System use zero-based register addresses? The sensor registers are
listed as zero based (starting from register zero); some Modbus master devices start from
register 1
– if this is the case, add 1 onto every register address listed in the manual.
Check that the sensor Serial Type has been set correctly, if set using other than Tan Delta
Configuration and Data Software, as a typical test, try to read the value back from any
(or all) of Registers 0 to 2 (zero based) or 1 to 3 (one based). These are the three live
readings.
2) Does your Monitoring System give communications errors? If so, check these to see if they
give any further indication of the issue. (eg. time-
out errors, CRC errors, overrun errors…)
3) What time-out is set within the Monitoring System? If this is too short the system may be
timing out before the sensor can respond. Time-outs of less than 50ms may cause
problems; 500ms to 1s are good starting points. If you are configuring the oil type via
Modbus then a timeout of 2000ms is recommended.
4) What polling rate is being used by the Monitoring System? If this is too short the system
may be asking for the next response before the sensor can respond to the first. Again
polling rates of something like 1s are a good starting point.
5) Does the Monitoring System use a standard Modbus 16 bit CRC for error checking? If not
the system will not communicate correctly.