Murphy MDTM89 One Thermocouple Only, Open Thermocouple Input, Using Thermocouple Extension Wire

MOUNTING DIMENSIONS

Mount the MDTM89 temperature SWICHGAGE® in a place where it will be protected from rain and splashing water. A minimum distance of 12 in. (305 mm) from any ignition coils or coil leads should be main- tained. The MDTM89 flush mount case is intended for mounting in a flat panel .032 in. (1 mm) to .125 in. (3 mm) thick.

First, cut a 4-3/4in. (121 mm) diameter hole and three 1/4 in. (6 mm) diameter fastening holes as shown below. Insert the SWICHGAGE® from the back side of the panel. Using the three 10-24 screws, included with the SWICHGAGE®, secure to the panel.

Front View

4-3/4 in.

(121 mm)

5-1/2 in.

(140 mm)

Side View

4-1/4 in.

(108 mm)

4 in. (102 mm)

Back View		Mounting Hole Pattern
Screw for	Remove Jumper(s)		4-3/4 in.
Equipment Ground	to Install
			(121 mm)
	Thermocouple

TC1		120
	120
TC2
		1/4 in.
		(6 mm)
		typical
	2-39/64 in. radius	diameter
	(66 mm)

WIRING AND ADJUSTMENT INFORMATION

CAUTION: Perform the wiring operation with the power source “OFF”. Make sure the voltage and current requirements are within the SWICHGAGE® ratings. Keep all high voltage wiring, such as spark plug wires away from THERMOCOUPLES

AND EXTENSION WIRING. Before wiring determine the voltage and polarity for the application.

One Thermocouple Only

Even though the MDTM89 is a dual temperature monitor, it will monitor and display one temperature with equal results.

When monitoring one temperature, always jumper the unused thermocou- ple terminals on the back of the MDTM89 with a short length of wire. The unused channel will display approximate ambient temperature.

Open Thermocouple Input

An open thermocouple input forces the monitor into upscale overrange. The monitor indicates an overrange by displaying the numeral “1” in the left most digit of the display. An overrange will turn on the trip point out- put, for the respective thermocouple.

MDTM89 Wiring and Adjustment Instructions

A.Using Thermocouple Extension Wire

1.After thermocouple installation, connect the thermocouple leads to

the MDTM89 according to the instructions. IMPORTANT: Use correct wire for the thermocouple selected.

USE ONLY THERMOCOUPLE EXTENSION WIRE.

2.If the thermocouple leads are not long enough you will need to use shielded thermocouple extension wire. The thermocouple extension wires, from your thermocouple lead wires to the terminals of the MDTM89, must be of the same material as the thermocouple lead wires. (See Table 1.)

Table 1. Thermocouple Extension Wire Color Code

Thermocouple	Thermocouple	Color Code/Material
Type	Extension Wire	Positive Lead	Negative Lead
J	Jx	White/Iron	Red/Constantan
K	Kx	Yellow/Chromel	Red/Alumel

Table 2. Thermocouple Extension Wire Loop Resistance in Ohms per Foot at 68°F

Size
	Type “J”		Type “K”
AWG No.
14	.07	.146
16	.137	.230
18	.222	.374
20	.357	.586
24	.878	1.490

Thermocouple lead length: 150 ohm lead resis- tance affects monitor accuracy less than 1°.

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