WattMaster WM-WCC3-TGD-01B - Manual (Page 799)

Operator Interface
VAV/Zone Controller Technical Guide
31
Troubleshooting
Figure 19: Typical TUC2R RS485 TUC Communications DC Voltage Measurements with the Loop
Connected - LT1785 Driver
Figure 20: Typical TUC2R RS485 TUC Communications DC Voltage Measurements with the Loop
Connected - 75176 Driver
The voltage measurements in Figure 19 are approximate voltages. Newer TUC2R controllers use a different RS485 driver chip. These voltage
measurements are taken when the power to the TUC2R controller is “ON” and the RS485 TUC communications loop is connected. These two
voltage measurements will fl uctuate slightly and will also momentarily “fl ip” to the other meter reading’s value. The voltage measurement from
“T” to “SHIELD” should be around 2.70 VDC. The voltage measurement from “R” to “SHIELD” should be around 3.00 VDC. Typical bad volt-
age measurement values would be anything above 3.8 VDC and anything below 1.5 VDC.
The voltage measurements in Figure 20 are approximate voltages. Older TUC2R controllers used a different RS485 driver chip. These voltage
measurements are taken when the power to the TUC2R controller is “ON” and the RS485 TUC communications loop is connected. These two
voltage measurements will fl uctuate slightly and will also momentarily “fl ip” to the other meter reading’s value. The voltage measurement from
“T” to “SHIELD” should be around 2.70 VDC. The voltage measurement from “R” to “SHIELD” should be around 3.00 VDC. Typical bad volt-
age measurement values would be anything above 3.8 VDC and anything below 1.5 VDC.