WattMaster WCC III part 10 - Manual (Page 17)

10. RS-485 COMMUNICATIONS
WCC III Technical Guide 10-15
TUC-2R Troubleshooting with a Digital Voltmeter
Figure 10-19: Typical TUC-2R RS-485 TUC Communications DC Voltage Measurements with the TUC COMM
Loop Connected – LT1785 Driver
Figure 10-20: Typical TUC-2R RS-485 TUC Communications DC Voltage Measurements with the TUC COMM
Loop Connected – 75176 Driver
The voltage measurements in Figure 10-19 are approximate voltages. These voltages are taken when the TUC2R controller is “ON” and
the RS-485 TUC communications loop is connected. These two voltages will fl uctuate slightly and also will momentarily “fl ip” to the
other meter reading’s value. The voltage measurements from “T” to “SHLD” should be around 2.70 VDC. The voltage measurements
from “R” to “SHLD” should be around 3.00 VDC. Typical bad voltage measurement values would be anything above 3.8 VDC and
anything below 1.5 VDC.
The voltage measurements in Figure 10-20 are approximate voltages. These voltages are taken when the TUC2R controller is “ON” and
the RS-485 TUC communications loop is connected. These two voltages will fl uctuate slightly and also will momentarily “fl ip” to the
other meter reading’s value. The voltage measurements from “T” to “SHLD” should be around 2.70 VDC. The voltage measurements
from “R” to “SHLD” should be around 3.00 VDC. Typical bad voltage measurement values would be anything above 3.8 VDC and
anything below 1.5 VDC.