Omega Vehicle Security OMP-MODL - Manual (Page 67)

3... I NTERFACE M ODULES
U SING THE OMP-MODL 3-43
nearly the same level of error compensation as the 4-wire
configuration with one less wire.
Due to the fact that only one of the lead wires resistance is actually
measured and the other lead wire is assumed to match, in using the
3-wire configuration, it is important that both lead wires used for the
excitation current (connected to terminals 1 & 2, or 7 & 8 and
opposite ends of the element) are of the same approximate length,
same gauge, and operating at the same temperature. The third lead
(connected to terminal 4 or 10) can be of lighter gauge if desired as
a very low current flows through it.
3-Wire Terminal Strip Connections:
As can be seen in the 3-Wire Wiring Diagram, each channel
requires 6 of the 12 terminals. Channel A uses terminals 1 through
6, and Channel C uses terminals 7 through 12.
Two matching gauge Excitation wires should connect from opposite
ends of the element and to terminals 1-2 or 7-8 on the module
terminal strip. A third Sense wire then connects from the element
(sharing the connection with a lead from terminal 1 or 7 on the
terminal strip) to terminal location 4 or 10. Two wire jumpers must
then be installed connecting terminals 2-3 and 5-6 for Channel A
and 8-9 and 11-12 for Channel C.
Refer to Chapter 6 for steps to generate a Terminal Strip Wiring
printout after construction of a Program Net for use in making field
wiring connections.
For long lead wire runs and in applications in electrically noisy
environments, it is recommended that twisted pair and/or shielded
wire be used. If shielded wire is used, the shield at the OMP-MODL
end should be connected to an external earth ground (Figure 3... -
29) or if available, a grounded Shield connection provided on
another type installed interface module (such as the MLIM-1).
2 1 12 11 10 9 8 7 6 5 4 3
RTD Element
Cable Shield
A C
Jumpers
3rd Wire used as SENSE lead
Connect Shield to an Earth Ground
ML126
Figure 3... -29: 3-Wire Configuration