ProTechTPS Total Protection System
Manual 26710V1
42
Woodward
Figure 2-13b. Example Configurable Input Wiring—Discrete Input (External
Power Option)
Configurable Discrete and Analog Inputs—Analog Input Wiring
When a configurable input is programmed to function as an analog input, it
accepts a two-wire, ungrounded, loop-powered signal, and must be wired as
shown in Figure 2-14 to function properly. The input impedance of the analog
input circuit, as indicated in Figure 2-14, is 200
Ω
. When configured as an AI,
twisted shielded pair wiring must be used. Refer to Chapter 3 (Functionality) of
this manual for information on how to program and use each analog input in an
application. Refer to the Chapter 3 (Functionality) of this manual for applicable
analog input specifications.
Because analog inputs are not fully isolated, take care in their application and
maintenance to avoid “ground-loop” type problems. If interfacing to a
non-isolated device with one of these inputs, the use of a loop isolator is
recommended to break any return current paths, which could result in erroneous
readings. Also, if a loop isolator is not used and the non-isolated field device has
a signal (or power) reference to PE ground connection, damage may occur to the
AI. Damage may occur during PE ground bounce or high current transient
ground fault conditions due to large potential differences in the remote PE ground
& the local PE ground.
For reliability reasons, Woodward recommends that input circuitry
for each module (A, B, C) be fully isolated from the input circuitry of
the other two modules. For example, the power source and wiring for
module A should not be shared or connected in any way to modules
B or C.
