Manual USDT Revsion 8 - Thermomax Technologies

Revision 

8 

THERMO TECHNOLOGIES 

USDT 2001 Differential Controller 

Installation and 

User’s Guide

USDT 2001 DIFFERENTIAL CONTROLLER 

Installation and User’s Guide 

Table of Contents 

Introduction 

General Information 1 

Installation 3 

Collector Sensor 4 

Tank Sensor 4 

Control Box 6 

Power Connection 7 

Sensor Connection 7 

Operation 

Control Mode 8 

Advanced Mode 9 

Diagnostics 10 

Characteristics Curves of Sensors 11 

© Thermo Technologies 

5560 Sterrett Place • Suite 115 

Phone 410.997.0778 • Fax 410.997.0779 

e-Mail info@thermotechs.com 

June, 2003

USDT 2001 INTRODUCTION 

Introduction 

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. 

T 

he USDT 2001 unit is designed to control a simple solar water 

heating system. By using microprocessor technology it ensures 

that the collected energy from the sun is transferred efficiently 

and harnessed under optimum conditions. It monitors collector 

temperature (T C ) and return temperature (T T , bottom of the storage 

tank). The solar loop circulation pump runs while the collector 

temperature exceeds the return temperature by a programmable 

temperature difference T. To avoid overheating, the circulation pump 

stops if the tank (T T ) temperature reaches the programmable high limit 

(T MAX ) temperature. To prevent freezing, the controller activates the 

pump and circulates water through the solar loop when frost conditions 

exist. The temperature hysteresis (a lagging in the set-point) may override 

T and can be modified in advanced operation mode to avoid pump 

cycling. 

The control unit has the following functions: 

• 2 inputs for temperature sensors 

• Suitable for sensors of type Thermistor and PT1000 

• All hysteresises are adjustable and depend on temperature 

• Adjustable (0 o F - 50 o F) frost protection 

• Adjustable (32 o F - 200 o F) overheating protection 

• Adjustable (1 o F – 50 o F) temperature difference T 

• Manual override of pump for system testing 

• Digital display of collector, tank, T, and maximum tank 

temperature 

• Indications of current state of pump 

• Surge protection at collector sensor 

1 

Thermo Technologies

USDT 2001 INSTALLATION 

General Information: 

USDT 2001 is suitable for Closed and Open Loop systems. Closed 

Loop Solar Heating Systems are the preferred option for extremely 

cold areas and areas with questionable water quality. Following 

arrangement shows an application example in a closed loop system. 

1. Collector 7. Check Valve 13. Pressure Gauge 

2. Collector Sensor 8. Hose Bibs for Filling and Flushing 14. Collector Supply 

3. Manual Air Valve 9. Expansion Tank 15. Heat Exchange Coil 

4. Hot Water to Taps 10. Air Purge and Air Vent 16. Solar Hot Water Tank 

5. Tempering Valve 11. Circulating Pump with flanges or couplings 17. Immersion Heater 

6. Collector Return 12. Pressure Relief Valve 18. USDT 2001 Controller 

Operation: 

USDT Controller (18) will switch on the pump (11) when the 

temperature at the collector sensor T C is higher than the return 

temperature T R by at least the pre-selected amount T. The pump 

circulates a heat transfer fluid around the loop. Heat from the 

collector is transferred to the storage tank through the heat 

exchange coil. With the pump running, if T is less than preset 

value, the pump will switch off. When a preset tank temperature is 

reached at T MAX , the controller can switch off the pump. The check 

valve (non-return valve) prevents heat from the tank rising towards 

the collector should the tank be warmer (e.g. at night). 

2 



INSTALLATION 

Note: This installation procedure is for guidance only, and the installer 

should verify its suitability. Make sure that the solar system is physically 

installed, manually tested, and is ready for controlled operation. 

T he following safety precautions are strongly recommended: 

1. Before attempting to install and operate the unit read this instruction 

manual carefully. 

2. Suitably qualified personnel should only carry out installation and 

any maintenance required. 

3. It is recommended that the unit be connected to the power supply 

via a suitably 6 amps isolating switch. 

4. WARNING: When the unit is connected to the 115-volt power 

supply and the cover is opened, high voltage circuits will be 

exposed. Therefore, when installing the unit (115-volt model) 

ensure all required connections are made and the cover is attached 

to the controller box before turning the power on. Ensure that all the 

connections made are secure. If any maintenance work is required 

ensure that the unit is isolated from the power supply before 

removing the cover. Never leave the unit unattended if the cover 

has been removed and the power supply is connected. 

5. Do not exceed unit ratings of 2.15 amps (1/6 HP or 245 Watts 

pump). 

6. It is advisable to route power cables away from sensor cables. 

3 



S ensor installation: For the system to function correctly, it is very 

important that sensors are located and installed properly. Make 

absolutely sure that they are completely pushed into the optional sensor 

pockets (not supplied). Sensors must be well insulated in order to 

prevent them from being influenced by the ambient temperature. 

When used outdoors, no water should be allowed to get into the 

immersion sleeves (lasting impedance change). Generally, sensors 

should not be exposed to moisture (e.g. condensation) as this can 

diffuse through the cast resin and damage the sensor. Heating at 

approx. 195 °F for one hour may possibly save the sensor . 

When sensors are used in open loops or swimming pools, make 

absolutely sure that immersion sleeves are corrosion-resistant. 

• Collector sensor (red cable): Either push into a sensor well 

(sensor pocket) which is soldered or riveted directly to the manifold 

(vacuum tubes) or absorber (flat plat collectors) that projects from the 

collector housing, or place a T-piece on the collector return outlet of the 

outer collector, insert an immersion sleeve (sensor well) into this 

together with cable connection cover (for moisture protection) and push 

into the sensor. For vacuum tube collectors, use of PT1000 sensors 

(480 °F max. temperature) is recommended. 

• Hot water tank sensor (white cable): In the case of external heat 

exchangers, the tank sensor should be installed with an immersion 

sleeve in return leg (cold side) of the heat exchanger. In tanks with 

integrated heat exchangers, the sensor pocket should be fitted at the 

exchanger's return outlet so that the immersion sleeve goes into the 

exchanger tube. 

• Clip-on installation: Best secured to the appropriate line with pipe 

clamps, clips, etc. whereby you must make sure that the material is 

suitable (non-corrosive, heat-proof, etc.). It is advisable to insulate the 

sensor well in order to measure pipe temperature accurately and to 

prevent any influence from ambient temperature. 

• Storage tank installation: The sensor required for the solar water 

heating system is installed in the lower part of the storage tank. As a 

reference sensor for heating hydraulics, it is advisable to push the 

sensor beneath the insulation - keeping close to the inner tank wall. 

4 



• Pool sensor installation: Place a heat conductive T-piece on the 

suction line directly at the pool outlet and screw in the sensor with an 

immersion sleeve (check corrosion resistance of the material used). 

Another possibility would be to attach the sensor at the same place by 

means of clips or adhesive tape, using appropriate thermal insulation 

against environmental influences. 

Sensor cables can be extended up to 150 ft. A connection between 

sensor and extension can be established as follows: 

Cut supplied heat shrinkable tubing to desired length (about ½”). Slide 

tubing over one end of wire to be sliced after removing enough outer 

insulation to accept the tubing. Then splice wire and slide tubing over 

splice. Heat gently all around until tubing shrinks tight. 

Slide larger tubing (about 3/4 “) over the entire completed splice. Heat 

gently all around until tubing shrinks tight. This connection can then be 

drawn easily into the pipe work. 

Caution: Do not overheat tubing! Remove heat as soon as tubing 

shrinks tight, as material will continue to shrink. With flame source, use 

even back and forth motion all around tubing. A heat gun may be used, 

if available. Let tubing cool for maximum strength. 

Sensor extension cable: Use 22/4 AWG telephone cable to extend 

collector sensor from collector to control unit. You need only two wires 

for sensor cable and the other two wires is considered as spare wires. 

5 



C ontroller unit installation: For viewing comfort, the controller 

unit should be positioned at eye level. It is always good practice 

to keep electronic equipment away from cold, and heat, as extremes of 

temperature may reduce the lifetime of the device. It is also good 

practice to keep electronic equipment away from heavy electrical loads, 

switches or contactors as these may cause electrical and 

electromagnetic interference when switched on or off. 

Undo the four screws at corners of the housing. The control electronics 

are mounted on the enclosure cover. Using proper fixing, the controller 

enclosure can be screwed to the wall with cable entry grommets 

downwards. 

Caution: Controller wiring should only be done when the unit is not 

energized. It is possible to damage the control unit if it is assembled 

under voltage. 

6 



P ower Connections and Wiring Diagram 

NOTE 1: Always disconnect the controller from power supply 

before opening the housing. 

NOTE 2: The controller should be properly grounded. Flexible wires, 

18/3 (gauge/conductor) simplify connection to the terminals. All 

connections should be secure and adequately tightened, as loose 

power connections will over-heat, and may cause fire. It is important 

that the specified output loads (245 Watts) are not exceeded. Where 

these loads expect to exceed, external relays must be used. It is good 

practice to install a 3 amps in-line fuse to protect controller and pump. 

Always keep power cables away from sensor cables and other low 

voltage signal cables. 

NOTE 3: To protect against lightning damage, the system must be 

grounded according local regulation. Sensor failures due to the weather 

or electrostatic are mostly due to poor grounding. 

NOTE 4: If step-down transformer is not mounted on the circuit board, 

the unit should be powered by a 24 VDC. A step-down transformer can 

be used also instead of DC power source, however, the open circuit 

voltage of AC source must be below 24 VAC. T C terminal should be 

connected to the Collector Sensor; T T should be connected to the Tank 

Sensor. The middle terminal is shared between both sensors. 

NOTE 5: The power supply is 115 V if step-down transformer is 

mounted on the circuit board. A load of maximum 3 A should be 

connected to the load terminals (pump) as shown in both above 

diagram and circuit board. 

7 


USDT 2001 OPERATION 

OPERATION 

Y our controller displays requested information one at a time. 

Selection indicator and its value blinks interchanged on unit’s 

display window. Push selection key (yellow) once to move to the next 

selection. Change set value by pressing the Set-Up (blue) key. 

NOTE: Holding selection key for two seconds brings the controller in 

advance programming mode. 

Collector temperature display 

Tank temperature display 

Press Set-Up key to increase T 

Factory Setting è 9.0 o F 

Range è 1 o F to 50 o F 

(Set Hysteresis value H1X, in advance mode, to 

H11 for smaller T values) 

Press Set-Up key for pump operation 

mode 

Aut è Automatic Mode 

On è Pump manually actvated 

OFF è Pump manually in off position 

Press Set-Up key to increase tank over 

heating protection temperature. Pump 

stops when tank temperature exceeds 

this value. 

Factory setting è 160 o F 

Range è 32 o F to 200 o F 

8 



ADVANCED MODE 

S etting mode – Press the selection key (yellow) for approximately two 

seconds to switch into the programming/setting mode. Software for 

solar water heating systems is stored in file P0. P1, P2, and P3 are program 

files for other applications. This manual covers only the solar water-heating 

program. 

Advancing – Press the selection key briefly to advance from one setting 

value to the next. 

Changing – Press Set-Up key once to increase the value. Hold it down to 

roll back to the lowest value after reaching the maximum value. 

Normal mode – To return to normal operating mode, press the selection 

key for two seconds while displaying P0. The system also returns to normal 

mode within one minute if no key is pressed. 

Software version number sequence 

Hysteresis curve for temperature differential control. 

H1x is for temperature difference and H2x is for maximum tank 

temperature curves with “x” as a corresponding value. Hysteresis 

curves (a lagging in the set-point) are variable and are a function of 

temperature. For example H14 (actual factory setting) means that the 

hysteresis of the maximum temperature is 4 o F at 64 o F (pump is on at 

60 o F and off at 64 o F) or 8 o F at 128 o F. 

9 



Hysteresis curves for tank temperature. 

Collector sensor selector - P refers to P1000 sensor 

Tank sensor selector – H refers to thermistor sensor 

Frost protection display. This value can be set from 0 to 

50 Fahrenheit. The factory setting is 0 Fahrenheit. Zero (0) disables the 

frost protection. 

Important: It is possible to change the software and its setting in advanced 

mode. All above values have been set in the factory. They generally do not 

have to be changed. Unauthorized changes may damage the properties of 

the control system entirely. Only experts should operate the unit in 

advanced mode. 

DIAGNOSTICS: 

Sensor failure; connection to sensor is lose. Open circuit 

conditions or wrong sensor attached. 

Sensor failure; sensor is short-circuited. 

10 


USDT 2001 Sensor Resistance vs. Temperature Table 

Temperature Tank Sensor PT 1000 Temperature Tank Sensor PT 1000 

[C] [Ohm] [Ohm] [F] [Ohm] [Ohm] 

0 1630 1000 32 1630 1000 

10 1772 1039 50 1772 1039 

20 1922 1078 68 1922 1078 

25 2000 1097 77 2000 1097 

30 2080 1118 86 2080 1118 

40 2245 1155 104 2245 1155 

50 2417 1194 122 2417 1194 

60 2597 1232 140 2597 1232 

70 2785 1271 158 2785 1271 

80 2980 1309 176 2980 1309 

90 3182 1347 194 3182 1347 

100 3392 1385 212 3392 1385 

11

Manual USDT Revsion 8 - Thermomax Technologies

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