Figure 6. 4-20mA Output Module Wiring Diagram
INSTALLATION INSTRUCTIONS FOR
SYMCOM’S 4-20mA OUTPUT MODULE
MODULE FUNCTIONS
The 4-20mA output module provides an analog output that is proportional to a selected parameter,
such as current or power. It must be used with a Model 777-AccuPower.
The 4-20mA module serves two very important functions. Its primary purpose is to convert the
communications signals from the microprocessor’s 5-volt levels into 4-20mA output, and to
electrically isolate the 4-20mA circuit from the high voltages present in SymCom’s units.
SymCom’s units are connected to high AC voltages with a floating ground circuit. As long as there
are three balanced line voltages present, the resulting ground level will often be near case ground.
However, if one phase is lost or if the line voltages become unbalanced, the floating ground may be
as much as 480 volts above the case ground. The 4-20mA module has optical isolation chips to
isolate the 4-20mA output from the AC line voltages.
The signals from the microprocessor go through resistors to provide current limiting before
connecting to the 9-pin external connector. Therefore, the 9-pin SUB D connector on the SymCom
unit provides un-isolated CMOS signals and is NOT RS232 or TTL compatible.
Note: Do not plug a modem or other PC compatible device directly
into the 9-pin SUB D connector on SymCom s units.
WIRING
The 4-20mA output module must be plugged in to the 9-pin connector on the Model 777-
AccuPower. Connect the + and – terminals to the load using 18-24 AWG twisted-pair cable. Connect
the shield to the terminal marked “S.” The 4-20mA output module is self-powered; no external
connections are required to energize the 4-20mA loop.
Terminal
Function
+
Positive 4-20 mA Output Connection
-
Negative 4-20 mA Output Connection
S
Shield Connection
Do Not Use
Do Not Use
Do Not Use
Do Not Use
Do Not Use
Do Not Use
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