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.
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. One model operates from 120 VAC by use of an isolation module 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
Either “J” or “K” type UNGROUNDED THERMOCOUPLE is accepted. Specify type in part number for each MDTM89 unit). You can also order thermocouples as a separate item.
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).
Automatic Cold Junction Reference
Open Thermocouple Input
An open thermocouple input forces the monitor into upscale overrange. The monitor indicates an overrange by displaying the numeral 1 (one) 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.
Continuous and Trip Point Display
The selector switch is used to select 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.