Universal Temperature Differential Controller

Download User's Manual in PDF Format



  • 2 inputs for temperature sensors
  •  Adjustable hysteresises on all inputs
  • Adjustable (0 oF to 41 oF) frost protection
  • Adjustable (200 oF to 299 oF) overheating protection
  • Adjustable (4.1 oF to 99 oF) temperature difference ∆T
  • Manual pump operation for system testing
  • Exchangeable 3.15 A system protection fuse
  • System diagnostic and status displays
  • Collector sensor surge protection
  • Digital display of all parameters

NOTE: The information presented in this page is for guidance only - no part of this may be used for any agreement, whether expressed or implied, or to form any contract. THERMO TECHNOLOGIES reserves the right to change specifications and prices without prior notice.

Universal Differential Controller

USDT 2004B is an advanced differential controller. It uses two temperature sensors to control a simple solar water heating system; one sensor measures the temperature of the solar collector whilst the second sensor measures the temperature at the bottom of the tank. It records and displays the collected energy in KWh units and programmable input/output temperature settings for pump control.

Suggested retail cost with two sensors - $159.00 plus s/h. Call VM with payment info for immediate shipping.


The USDT 2004B monitors and displays supply and return temperatures. When the supply temperature exceeds the return temperature by a programmable temperature difference (∆T), an internal relay can power a ¼ HP pump or an auxiliary relay.
To avoid overheating the controlled system, the pump stops when the supply temperature reaches a programmable maximum temperature (TMAX).  Frost or cooling protection is regulated through return temperature monitoring. Regardless of the temperature difference (∆T), the pump runs when the return temperature is below a programmable minimum temperature (Tmin).  The system offers an adjustable temperature hysteresis to avoid pump cycling.

Power Connection
  • Power supply 120 V AC
  • Maximum load 3.15 A (75 W)
  • Phantom load max. 2 W
  • A surge arrester at the collector sensor reduces lightning damages to the controller internal electronics 

Sensor Characteristics

  • The unit is supplied with two thermistor sensors
  • Sensor cables can be extended up to 500 feet using standard two wire cables
  • Collector sensor is supplied with a weather resistant terminal box and EMI impedance protector
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