Thermo Products USDT 2004B U,

Note: The information supplied in this manual is for guidance only - no part of this may be used

for any agreement, whether express or implied, or to form any contract. Thermo Technologies

reserves the right to change specifications without prior notice.

SDT 2004B is a powerful temperature differential control unit. 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.

The control unit has the following basic functions:

• 2 inputs for temperature sensors

• Hi/Low adjustable factory-set temperature programming

• Adjustable (4.1 o F to 99 o F) temperature difference ?T

• Manual override of pump for system testing

• Digital display of all parameters

• System status and diagnostic displays

Operation

The controller uses two sensors. One sensor (S1 in diagram) monitors the collector temperature

whilst the other sensor (S2) monitors the temperature at the bottom of the storage tank. The solar

loop circulation pump runs while the collector temperature

exceeds the tank temperature by an adjustable temperature

difference diff. To avoid overheating, the circulation pump

stops if the tank temperature reaches the adjustable high

limit (TMAX

) temperature.

The pump A1 runs only when the temperature at the

collector sensor location S1 is higher than the return

temperature at location S2 by at least diff (?T). The pump

stops if diff is less than the preset value or, when the

temperature at location S2 has reached the TMAX :

A1 (ON) only when S1 > (S2 + diff) & S2 < T max