Omega Vehicle Security OMP-MODL manual Gnd

3... INTERFACE MODULES
	+ XTMR -		+	4-20mA	-
				Panel Meter		Terminal Strip
					1	2	3	4	5	6	7
					+	-		+	-
						A			B
	4-20mA			+ XTMR -
+ Controller		-
+	Power		-		GND
	Supply
											ml057

Figure 3... -16: Terminal strip connections for multiple 4-20mA inputs

To minimize noise pickup on sensor wiring between the OMP-MODL and the end sensor or signal source, 18 to 22 AWG shielded, twisted pair wire is recommended. At the low current levels input to the MLIM-1, voltage drop in signal wiring is not a concern, however for extremely long runs, a voltage drop analysis should be performed for the entire loop and if necessary larger gauge wire should be used.

FYI: Typically, with current signals (in contrast to low level voltage signals), noise pickup will be less due to the low impedances involved in the circuit. However, in real- world applications, one should attempt to minimize noise on signal wires whenever possible... remember, Mother Nature loves to throw surprise parties.

Shielded wire minimizes the amount of noise picked up by the internal conductors carrying the signals by providing an `electrical shell’ or Faraday cage around the internal conductors.

Twisted pair wiring exposes both conductors equally to the ambient electrical noise. This common-mode type noise is easier to reject by the Interface Modules input signal conditioning circuitry than un-balanced (or differential) noise.

Shielding and/or twisted pair wire is especially recommended in electrically noisy environments for optimum signal protection. If shielded wire is used, a ground wire should be run from the MLAD-1 module Chassis Ground (terminal strip connection #16) to an earth ground connection to conduct away noise picked up by the wiring shield (Figure 2-8). Only one ground wire is required as all of the Shield terminal strip connections are

3-28 USING THE OMP-MODL