Sensaphone SCADA 3000 Users manual - Manual (Page 247)

23-3
Chapter 23: Universal Input Module
It is extremely important that the EG pin be connected to a good earth ground. This will pre-
vent communication errors due to differences in ground potential between modules in addition
to possible damage due to voltage transients and surges.
The two LED lights in the center of the module, marked Power and Pulse indicate that the
module is receiving power and operating properly. The Pulse LED will blink at a regular rate,
like a heartbeat, once it establishes communication with the main unit.
The module generates a 24V power supply for use with 4–20mA transducers. Module power
consumption will vary depending on how much power is being drawn from this supply. For
estimation purposes add 38mA to the power consumption specification for every 4–20mA
loop powered by the module. For example, since the module consumes 100mA by itself, if two
4–20mA transducers are connected to the 24V supply, then the estimated total power con-
sumption should be 176mA.
Communications Wiring
The Universal Input Module communicates with the SCADA 3000 using a high-speed serial
communications bus. This 4-wire bus is used to connect up to 15 modules to the main unit to
provide additional inputs and/or outputs. Perform all wiring with power to the main unit and
modules turned off.
Modules may be located a maximum of 2000' away from the main unit and should be con-
nected in a daisy-chain fashion from one module to the next. Each module connects to the
next via a 4-wire communications cable connected to the terminals labeled A,B, Y & Z. The
cable must be 4-Conductor Twisted Pair (shielded or unshielded) with a nominal impedance
of 120Ω (for example, Belden #8132 or 9842 cable). Use one pair for A & B and the other pair
for Y & Z. The proper wiring from the main unit to the modules, and from module to module,
is shown in Figure 3:
Figure 3: Correct daisy chain setup: Main unit on the end.
Figure 4: Incorrect daisy chain setup: Main unit in the middle of the chain.
The Main Unit should always be on one end of the chain, never in the middle.