WattMaster WM-WCC3-TGD-01B - Manual (Page 798)

VAV/Zone Controller Technical Guide
Operator Interface 30
Troubleshooting
TUC2R Communications Troubleshooting with a Digital Voltmeter
The voltage measurements in Figure 17 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 disconnected. These two
voltages will not fl uctuate. The voltage measurement from “T” to “SHIELD” should be around 3.25 VDC. The voltage measurement from “R”
to “SHIELD” should be around 3.25 VDC. Typical bad voltage measurement values would be anything above 3.8 VDC and anything below 1.5
VDC.
Figure 17: Typical TUC2R RS485 TUC Communications DC Voltage Measurements with the Loop
Disconnected - LT1785 Driver
Figure 18: Typical TUC2R RS485 TUC Communications DC Voltage Measurements with the Loop
Disconnected - 75176 Driver
The voltage measurements in Figure 18 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 disconnected. These two
voltages will not fl uctuate. The voltage measurement from “T” to “SHIELD” and from “R” to “SHIELD” should be around 2.50 VDC. Typical
bad voltage measurement values would be anything above 3.8 VDC and anything below 1.5 VDC.