MOD-TRONIC MT300 3 Channel Transformer Temperature Monitor
RTD or Thermocouple Input Monitor designed for the dry transformer market

Transformer Temperature Monitor MT300 from Mod-Tronic has three channels and accepts both RTD and Thermocouple inputs

MOD-TRONIC's new MT300 consists of a three channel transfomer temperature monitor and alarm system that controls three relay outputs based on user-programmable set points to help safeguard expensive transformers and machinery.


The MT300 provides users a completely programmable transformer temperature monitor and alarm with improved measurement range of -50°C to 300°C (-58°F to 572°F) and universal inputs of either 100Ω or 1000Ω Platinum RTDs or Types E or K thermocouples. The microprocessor-based design maintains accuracy over a wide range of temperatures and conducts regular self-checks to ensure correct operation. Additionally, one of the relay outputs is specifically designed for control of a cooling fan with a 30 Amp rating. The user-configurable fan exercise option extends the fan life and reduces bearing lock-up. The monitor is easily configured via MODBUS over a USB connection to your PC or MODBUS/RS-485 using the included PC software that also provides data logging.

Other key features include:

  • Universal inputs of 100 and 1000 Ω platinum RTDs and Types E and K thermocouples
  • Easily configurable via the front-panel interface, MODBUS over USB or the isolated RS-485, PC software included for data logging and configuration
  • User-configurable measurement range to Celsius or Fahrenheit scale
  • Large, dimmable 7-digit LED display allows easy programming and visibility at various distances and lighting conditions
  • Dual password design allows certain users to have full configuration access and others, set points only
  • Non-volatile memory storage of per-channel min/max temperatures for recall in the event of power-loss
  • Electrically isolated 4-20mA output signal allows for connection to PLCs or remote displays
  • Made in the USA
  • UL/cUL recognition
  • 5 Year Warranty

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Setup Worksheet
Version 1.0 Software (If the newer version above does not work on your system)



MOD-TRONIC’s MT300 transformer temperature monitor and alarm is designed with the specifications for dry-type transformer monitoring and protection. Additional applications include use in pumps, compressors and motors.

Ordering Options


AC power, 120-240VAC, 50-60Hz, 120-240VDC


DC power: 21-36VDC

Technical Specifications


Sensor Input Types

Programmable selection of:


RTD: 100 or 1000 Ω platinum .00385 TCR
















Thermocouple: Type E or K

Measurement Range

-50°C to 300°C (-58°F to 572°F), 1°C resolution, 2°C full-range accuracy

Relay Contact Ratings

Voltage: 240V AC

Fan Relay: SPST, 30A @ 240VAC or 1.5HP @ 55°C,derates to 22A or 1.5HP @ 72°C

Trip Relay: SPDT, 10A @ 240 VAC

Alarm Relay: SPDT, 10A @ 240 VAC

Current Loop Outputs

Isolated, industry-standard 4-20mA current-loop output for forwarding of reading to PLC or remote indicator.

Configuration: high value, low value, specific channel selection.

Scaling: Offset from -50°C to 250°C, span from 50°C to 350°C

Error signaling: 3.5mA or 23mA output during sensor failure.

Power: isolated loop power –or– non-isolated self-power


MODBUS over USB or isolated RS-485, RTU, 300-38400bps


UL/cUL recognized


Sensor Inputs

Note: “Universal” inputs are standard and are electrically isolated from control logic and communications.

RTD: 100Ω or 1000Ω Platinum, 0.00385Ω/Ω/°C TCR, 2- or 3-wire connection, Open and shorted sensor detection

Thermocouple: Type K or Type E thermocouple, open detection.

Temperature Range

-30°C to 72°C (-22°F to 162°F), 95% humidity, non-condensing

Output Relays

Connection: terminal block, 30 AWG to 10 AWG wire


User Interface

Display: LED, 7-segment, red, 0.56” height, dimmable

Indicators: LED, red: Fan, Trip, Alarm, Peak, Manual Fan, Test


Front-panel: 6.3” x 9.9”

Cut-out: 5.67” x9.17”

Depth: 1.9”


Metal, corrosion-resistant.
NEMA 4 front panel