Omega Vehicle Security OMP-MODL manual As can be seen in the 3-Wire Wiring Diagram, each channel

3... INTERFACE MODULES

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

				A						C
3rd Wire used as SENSE lead
	1	2	3	4	5	6	7	8	9	10 11 12
RTD Element
								Jumpers
Cable Shield				Connect Shield to an Earth Ground
										ML126
Figure 3... -29:	3-Wire Configuration

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).

USING THE OMP-MODL 3-43