WattMaster WCC III part 10 - Manual (Page 18)

10. RS-485 COMMUNICATIONS
WCC III Technical Guide 10-16
VAVZ II Troubleshooting with a Digital Voltmeter
Figure 10-21: Typical VAVZ II RS-485 TUC Communications DC Voltage Measurements with the TUC COMM
Loop Connected – LT1785 Driver
The voltage measurements in Figure 10-21 are approximate voltages. All VAVZ II controllers should use the LT1785 driver chip. These
voltages are taken when the VAVZ II 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 voltages measurements
values would be anything above 3.8 VDC and anything below 1.5 VDC.
Figure 10-22: Typical VAVZ II RS-485 TUC Communications DC Voltage Measurements with the TUC COMM
Loop Disconnected – LT1785 Driver
The voltage measurements in Figure 10-22 are approximate voltages. All VAVZ II controllers should use the LT1785 driver chip. These
voltages are taken when the VAVZ II controller is “ON” and the RS-485 TUC communications loop is disconnected. These two voltages
will not fl uctuate. The voltage measurements from “T” to “SHLD” should be around 3.25 VDC. The voltage measurements from “R” to
“SHLD” should be around 3.25 VDC. Typical bad voltages measurements values would be anything above 3.8 VDC and anything below
1.5 VDC.