Omega-vehicle-security OMP-MODL Manuel d'utilisateur télécharger pdf (Page 67)

3... INTERFACE MODULES

USING 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).

21 1211109876543

RTD Element

Cable Shield

Jumpers

3rd Wire used as SENSE lead

Connect Shield to an Earth Ground

ML126

Figure 3... -29: 3-Wire Configuration

1 2 ... 62 63 64 65 66 67 68 69 70 71 72 ... 296 297

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Omega-vehicle-security OMP-MODL Manuel d'utilisateur Page 67