Omega Vehicle Security OMP-MODL manual Wire Configuration

4-Wire Config

3... INTERFACE MODULES

4-Wire Configuration

The 4-wire configuration is used in applications where the lead wire effects calculated as above will have a significant error inducing effect on the resistance measurement. The 4-wire configuration provides the best compensation for lead wire resistance at the expense of running a 4th lead. The 4-wire configuration requires two input channels (A and B or C and D) to implement. From within the HyperNet Window, double-clicking Channel A or C icons displays a dialog and allows for selection of 2, 3, or 4-wire connection. When 4-wire is selected, a second corresponding icon (Channel B or D) is removed as this second channel is required for the 4-wire measurement.

4-Wire Compensation Theory:

With a 4-wire configuration, the excitation current flows to and from the element through one pair of leads. The actual voltage developed across the element is then measured using a second pair of Sense leads that conduct a very small amount of current (hence adding negligible I * R voltage measurement error) .

The 4-wire configuration, as the name implies, requires the use of four discrete wires from the module terminal strip to the element. Two of the leads connect to one end of the element and the other two to the other end of the element.

Due to the fact that the excitation current flows through a separate pair of leads, wire gauge, temperature effects, and connection resistance has no effect on the accuracy of the readings. The Sense leads (connected to terminals 4-5 or 10-11) can be of lighter gauge if desired as a very low current flows through them.

4-Wire Terminal Strip Connections:

As can be seen in the 4-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.

The Excitation wires connect from opposite ends of the element and to terminals 1-2 or 7-8 on the terminal strip. A second pair of Sense wires then connects from opposite ends of the element to terminals 4-5 or 10-11. A wire jumper must then be installed connecting terminals 2-3 for Channel A and 8-9 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.

3-44 USING THE OMP-MODL