MDTM89

Temperature Sensors and Instruments

Monitor inputs from two thermocouples
Adjustable switch trip point for each input
FET or SCR output
Power from CD ignition or 120 VAC or 12/24 VDC
Types “J” or “K” ungrounded thermocouples
Digital readings in Fahrenheit or Celsius

OVERVIEW:

Murphy’s model MDTM89 is an electronic, dual-temperature monitor. It monitors two thermocouples, displays the temperature of the thermocouple selected and has adjustable trip points for each input. A toggle switch provides for selection of the thermocouple to be displayed and/or the temperature trip point to be checked/adjusted. If either trip point is reached, the associated output turns on and can be used as a control signal or to initiate alarms and/or shutdown.

A Push to Read button, located below the selector switch, allows the operator to check the trip point and to see its value as adjustments are made. Two potentiometers, one on each side of the thermocouple selector switch, are provided for field adjustment of the trip points.

Applications
There are four basic models. Two of the models are powered by capacitor discharge ignition and have either an FET or an SCR output. One model operates from 12- or 24-VDC and has an FET output. Standard display is in degrees Fahrenheit; degrees Celsius is optional.

Applications include the following:
Compressor suction/discharge temperature
Engine/compressor jacket water temperature
Engine exhaust temperature
Compressor cylinder temperature
After cooler temperature
Bearing temperature

Thermocouple Type
Either J or K type UNGROUNDED THERMOCOUPLE is accepted. Specify type in part number for each MDTM89 unit (see How to Order). Order thermocouples as a separate item.

Continuous & Trip Point Display
The selector switch is used to choose the thermocouple or trip point temperature to be displayed. The selected temperature is continuously displayed during normal operation. Depressing the Push to Read push button displays the trip point temperature of the selected thermocouple.

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 high trip point output.

Trip Point Operation
Monitored trip points are independent of the thermocouple selector switch. Both set points are always active.

When the thermocouple temperature reaches the trip point temperature, the MDTM89 is triggered. After approximately 0.5 seconds the trip point output turns on.

Trip points are set by depressing the Push to Read push button while rotating a trip point potentiometer until the desired trip point temperature is displayed.

Automatic Cold Junction
Cold junction reference point compensation is an integral feature of the monitor. The compensator circuit monitors case temperature and automatically compensates for changes in ambient temperatures. Compensation will allow maximum of 2 degrees change in the temperature reading from 32° to 122°F (0° to 50°C).

SPECIFICATIONS:

Power Requirements (Operating Voltages):
- MDTM89-A: 100 to 350* VDC, CD ignition, negative ground (FET outputs)
- MDTM89-E: 100 to 350*, CD ignition, negative ground (FEToutputs)
- MDTM89-B: 100 to 350* VDC, CD ignition, negative or positive ground (SCR outputs)
- MDTM89-C: 12 to 24+ VDC, negative ground, 15 milliwatts (FET outputs)
Power Consumption: CD ignition: 350 μa @ 100V; 120 VAC: 0.6 watts; 24 VDC: 0.5 watts
Outputs:
- Model B: output turns on above trip point; output turns off when power is switched off; two (2) isolated SCR outputs, 0.5 amp @250 VDC
- Models A, C and D: output turns on above trip point; output turns off below trip point; two (2) isolated FET outputs, 0.5 amp @ 250 VDC
- Model E: output one turns on above trip point, output turns off below trip point: output 2 turns on below trip point, output turns off above trip point: two (2) isolated FET outputs, 0.5 amp @ 250 VDC
Ambient Cold Junction Compensation Range: 32° to 122°F (1°C from 0° to 50°C)
Operating Temperature: -4° to 158°F (-20° to 70°C)
Storage Temperature: -40° to 300°F (-40° to 150°C)
Case: Die cast aluminum
Reset Differential: FET models: Decreases 3° (°F or °C).
SCR model: turn input power off to reset.
Measurement Range: Monitor Range 0°-1999°F or °C (specify F or C in part number)
Accuracy: With J-type thermocouple: from 150°-1200°F (66°-649°C) ±1.5% of reading. With K-type thermocouple: from 400°-2000°F (204°-1076°C) ±1.5% of reading. At calibration temperature.
Laboratory Approvals: CSA† and Factory Mutual* approved for Class I, Division 2, Group D, hazardous locations).
Thermocouple Lead Length: 150 ohm lead resistance affects monitor accuracy less than 1°
Trip Point Accuracy: ±3°F (±2°C) of reading
Trip Point Adjustment Range: 0-1999 Degrees
Shipping Weight: 48 oz. (1.4 kg)
Shipping Dimensions: 10 x 9-1/2 x 6 in. (254 x 241 x 152 mm)