WattMaster WCC III part 10 - Manual (Page 15)

10. RS-485 COMMUNICATIONS
WCC III Technical Guide 10-13
SAT 3P Troubleshooting with a Digital Voltmeter
Figure 10-15: Typical SAT 3P TUC RS-485 Satellite Communications DC Voltage Measurements with the SAT
COMM Loop Connected
The voltage measurements in Figure 10-15 are approximate voltages. All SAT 3P controllers should use the LT1785 driver chip. These
voltages are taken when the SAT 3P controller is “ON” and the RS-485 SAT 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 10-16: Typical SAT 3P TUC RS-485 Satellite Communications DC Voltage Measurements with the SAT
COMM Loop Disconnected
The voltage measurements in Figure 10-16 are approximate voltages. All SAT 3P controllers should use the LT1785 driver chip. These
voltages are taken when the SAT 3P controller is “ON” and the RS-485 SAT 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.