DE2643658A1 - TEMPERATURE CONTROL DEVICE - Google Patents

Description

HOFFMANN · EITLE & PARTNER -

PATENT LAWYERS DR. ING. E.HOFFMANN ■ DIPI.-ING.W.E1TLE - DR.REK.NAT. K.HOFFMANN · DlFU-lMG. ^. IEllN D-ISOOO MÖNCHEN 81 - ARABELLASTRASSE 4 (STERNHAUS) - TELEPHONE (089) 911087 - TELEX 05-27 «» IPATHE)

German Ranco GmbH, Hockenheim

Temperature control device

The invention relates to a temperature control device with a temperature control unit, a safety switching unit and a temperature display. Such temperature control devices are used in particular in heating systems, hot water extraction systems and the like, but can be used in modified form can also be used for cooling systems.

Known temperature control devices of this type have at least two temperature sensors, namely one temperature sensor for the temperature control unit and a temperature sensor for the safety switching unit. For the temperature display is a further temperature sensor provided. The temperature sensors are mechanical or liquid-filled sensors and the safety switching unit, which has to ensure that a certain maximum temperature is not exceeded in any case usually an electromechanically constructed unit- The temperature control unit is usually an electromechanical or

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/ NSPECTED

an electronic unit. If the temperature control unit is an electronic unit, a signal converter must be used to convert it of the temperature signal coming from the temperature sensor can be provided in an electronically processable signal .

As a result of the low security of known temperature control devices it was previously common and sometimes required to provide at least two temperature sensors. Besides, it is It is common in known temperature control devices to provide a manual reset of the safety switching unit.

The invention is based on the object of a temperature control device of the type described at the beginning, which is easier to assemble, easier to assemble, to maintain and, if necessary, to is to be repaired and which has a greater operational and shutdown reliability.

This object is achieved in that a single Temperature sensor is provided, which is a thermistor and is connected to an electronic bridge circuit, that the electronic bridge circuit controls two operational amplifiers, which in the temperature control unit and in the Safety switching unit are provided, and that the operational amplifier Operate two switching units switching in opposite directions.

The use of a single temperature sensor has the advantage that the exact for all functions of the temperature control device is based on the same measured variable. The use of a thermistor as a temperature sensor makes it possible to use the temperature sensor directly to be integrated into the electronic bridge circuit. The use of the electronic bridge circuit in conjunction with the two operational amplifiers ensures that in the event of failure of individual circuit elements of the bridge circuit a switch-off command is given. Because the operational

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the amplifier actuate two switching units switching in opposite directions, On the other hand, it is ensured that a failure of one of these switching units leads to a shutdown of the entire Temperature control system leads.

The temperature control device is expediently constructed so that the switching units are relays and that the relay of the Temperature control unit has closed current contacts and the relay of the safety switching unit has working current contacts. at such a temperature control device are the associated with a feed of the relay of the temperature control unit Relay contacts open, which means that the temperature is no longer increased. Feeding the relay of the safety switching unit leads to the closing of its contacts, which leads to the system being switched off. Should the If the contacts of the relay of the temperature control unit are welded together, the temperature rises until the relay the safety switching unit switches off the system. On the other hand, should the contacts of the relay of the safety switching unit weld together, this leads to a shutdown of the system.

The electronic bridge circuit expediently has at least three voltage dividers, one of which contains the thermistor. The second voltage divider advantageously contains the thermistor, while the first and second voltage dividers a first diagonal voltage bridge for controlling the temperature control unit and the second and third voltage dividers are a diagonal voltage bridge for controlling the safety switching unit form.

The second voltage divider and a fourth voltage divider can also be used form a measuring bridge to which. ' a display instrument for the temperature is connected. A change of the resistance value of the thermistor contained in the second voltage divider detuned the measuring bridge and leads to

a temperature display on the display instrument.

The structure of the electronic bridge circuit with at least three voltage dividers, which two diagonal voltage bridges form, has the result that in the event of a short circuit in the thermistor, the safety switching unit responds and the system is switched off is to respond to the safety switching unit To ensure that the thermistor also breaks, it is advisable to place a switch between the thermistor and the operational amplifiers Safety circuit responsive to a thermistor break is provided. This safety circuit is preferably between the center tap of the second voltage divider and the operational amplifiers intended.

A circuit for monitoring the operational amplifier is also expedient in the output of the operational amplifier of the safety switching unit intended. This circuit releases the safety switching unit in the event of a short circuit in the input of the operational amplifier off, which switches off the system.

Finally, the electronic bridge circuit is the one according to the invention Temperature control device preferably constructed in such a way that that jointly adjustable potentiometers are provided in the first and third voltage divider. These potentiometers are used the joint setting of the control or response range of the temperature control unit and the safety switching unit.

The temperature control device according to the invention offers the advantage a very simple and cheap structure of the temperature sensor. In addition, a quickly responding control can be achieved, which cannot be achieved by electromechanical means is. This is particularly important for modern systems with a small water reservoir, in which rapid temperature increases appear.

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The circuit of the temperature control device according to the invention provides the security that the system will work in the event of a temperature sensor or a line break, a temperature sensor short-circuit, or failure of the circuit elements and the switching units or welding of the relay contacts and in the event of failure of the operational amplifier always turns off. By using only a single temperature sensor to control the temperature control unit and the safety switching unit ensures that the safety switching unit is always fully operational. If an error occurs, the temperature control device always switches to the safety side, i.e. the system will always switched off.

An embodiment of the invention is shown in the drawing and is described in more detail below. Show in the drawing

Fig. 1 is a block diagram of a temperature control device according to the invention,

Fig. 2 four voltage dividers, which in the temperature control device interconnected according to Fig. 1 to two diagonal voltage bridges and a measuring bridge are and

Fig. 3 is a circuit diagram of the temperature control device according to Fig. 1.

In Fig. 1 the block diagram of a preferred embodiment of a temperature control device according to the invention is shown. A power supply unit 5 feeds four voltage dividers 1, 2, 3 and the voltage divider 2 is influenced by a temperature sensor 6. This influencing takes place in that a thermistor ^, _{TC is} provided as the temperature sensor 6, which thermistor forms part of the voltage divider 2.

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The voltage divider 2 and the voltage divider 4 together form a measuring bridge, ^a ^ to which a display instrument 7 is connected.

The voltage divider 1 and the voltage divider 2 together form a first diagonal voltage bridge, which is connected to a first operational amplifier 9 via a safety circuit 8 is. The operational amplifier 9, designed as a differential amplifier, operates on a relay 10 with closed-circuit contacts. When the operational amplifier 9 is switched through, the contacts of the relay 10 are opened. The operational amplifier 9 together with the associated wiring and the relay 10 represent the temperature control unit 11 of the temperature control device. Opening the contacts of relay 10 interrupts the temperature rise of the system.

The voltage divider 2 and the voltage divider 3 together form a second diagonal voltage bridge. Which, via the already mentioned safety circuit 8, also acts as a differential amplifier formed second operational amplifier is connected. The operational amplifier 12 works on second relay 13, which, however, has operating current contacts. When the operational amplifier 12 is switched through the contacts of the relay 13 closed and the system switched off. The system can only be switched on again when a switch-on lock 14 has been released manually. The operational amplifier 12 together with the associated circuitry, the relay 13 and the switch lock 14 together form the safety switching unit 15 of the temperature control device.

In Fig. 2, the four voltage dividers of the electronic bridge circuit are shown. The voltage divider 1 contains a resistor R ₁ ~ i- ^m a voltage divider branch and in the other voltage divider branch a resistor R-, ₃ * which is connected to the parallel connection of a resistor R ₁ . and an adjustable potentiometer P _{3 1 is connected} in series.

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The voltage divider 2 contains a resistor R _g in one voltage divider branch and the parallel connection of a thermistor iCrmp ^with a resistor R ₇ in the other voltage divider branch. The voltage dividers 1 and 2 are interconnected in the bridge circuit to form a diagonal voltage bridge, the points B and D of which are led to the first operational amplifier 9.

The voltage divider 3 contains a resistor R ₁₀ in series with the parallel connection of a resistor R _1ς and an adjustable potentiometer P ₃ 2 ^ ^m a voltage divider branch and a resistor R ₁₁ in the other voltage divider branch. In the bridge circuit, the voltage dividers 2 and 3 are interconnected to form a second diagonal voltage bridge, the points C and D of which are led to the second operational amplifier 12.

The fourth voltage divider consists of a resistor .Rgim a voltage divider branch and a resistor R _q in series with an adjustable potentiometer P ₂ in the other voltage divider branch. The center tap of the voltage divider 4 is led to a point E _{via an adjustable potentiometer P 1.} The voltage dividers 2 and 4 together form a measuring bridge, between whose points E and D the display instrument 7 for the temperature is located.

In the electronic bridge circuit of the temperature control device, the points P of the voltage dividers 1, 2, 3, 4 are on the positive lead coming from the power pack 5, while the points N are on the negative lead coming from the power pack 5.

Fig. 3 shows the circuit diagram of the temperature control device described, via a safety transformer Tr ₁ , the AC voltage of the network is fed to a bridge rectifier n1, which rectifies the AC voltage. A smoothing capacitor C_ is connected via the output of the bridge rectifier n1 and, with the interposition of a resistor R _16, a

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stabilizing Zener diode D- connected. The so far to Fig.? The circuit elements described form the power supply unit 5.

The four voltage dividers 1, 2, 3, 4 described in more detail in connection with FIG. 1 are connected to points P and N. The voltage dividers 1 and 2 form a first diagonal voltage bridge, the output of which is the points D and B. The voltage dividers 2 and 3 form a second diagonal voltage bridge, the output of which is the points D and C. A Zener diode D is connected in series with a resistor R _{1Q between point D and point N.} Further point D is via a counter

I ο

stood R * connected to a point A. Between point A and the point N is the emitter-collector path of a transistor T-, the base of which is at the connection point between the Zener diode

D ^. and the resistance R " _o lies,
ο Io

_{The circuit elements} D ,, R 1o, R. and T ₁ form the safety circuit 8. As long as this safety circuit 8 does not respond, the potential at point A is equal to the potential at point D.

The first diagonal voltage bridge is balanced when the resistance values of voltage dividers 1 and 2 correspond in such a way that that the output voltage between points D or A and B is zero. In this case the following equation must be fulfilled:

_r . 7 NTC ₌ . , ^P 31 ' ^r 14 ^{12 r} 7 ^{+ r} NTC ^{6 13} P ₃ 1 ^{+ r} i4

Here, as in the following, r and ρ are the resistance values the corresponding resistors and potentiometers with the same indices.

The second diagonal voltage bridge is balanced when the resistance values of voltage dividers 2 and 3 correspond in such a way that that the output voltage between points D and

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A and C is zero. In this case the following equation must be fulfilled:

r + ^P 32 * ^r i5 ^r 7 ' ^r NTC ₌

^r 10 ⁺ ρ + χ r_ + r " _m " ^L 6 11

A change in temperature at the thermistor R ^ p detunes the two Diagonal tension bridges; this creates tensions at the exits of the diagonal tension bridges between points A, B and C. Point A is connected to an inverting input of each operational amplifier 9 and 12, which is point B. to a non-inverting input of the operational amplifier 9 and point C to a non-inverting input of the Operational amplifier 12 switched.

The voltage divider branches are dimensioned so that when one set for the temperature control unit 11 Temperature, the potential at point A drops below the potential at point B. This switches the operated as a threshold switch Operational amplifier 9 with the output at H potential, whereby the relay 10 is de-energized, i.e. its closed-circuit contacts be opened.

If the potential at point C exceeds the potential at point A, the operational amplifier 12 switches the output to Η potential, whereby its output voltage _{exceeds the Zener voltage of a Zener diode D 1} in the output of operational amplifier 12. This creates a voltage THYI at the gate of a subsequent thyristor. The thyristor THYl is ignited, the relay 13 has a current flowing through it, ie the working current contacts of the relay 13 are closed. This shuts down the system. This state is maintained until a push button b1 located in the circuit of the thyristor THY1 and the relay 13 is actuated in such a way that the thyristor is de-energized for a short time, whereby the relay 13 is also de-energized. The thyristor THY 1

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blocks until voltage is applied again to its gate. The push button b1 is designed or attached so that it can only be actuated with the aid of a tool or a key. The Zener diode D ₁ ensures that the thyristor THY1 only ignites when the operational amplifier 13 goes to Η potential.

If a break occurs in the temperature sensor, ie the thermistor R _n - or in the sensor line, the potential at point D goes to its maximum value and exceeds the voltage of the Zener diode O _c , so that the transistor T .. becomes conductive and on Point A zero potential is present. Thus, the potentials at points B and C are greater than at point A and the operational amplifiers 9 and 12 switch to Η potential, so that the relay 10 is de-energized and the relay 13 is energized. The system is switched off. This state is retained until the fault has been rectified by a specialist and the switch-on lock is released by pressing pushbutton b1.

If the temperature sensor, i.e. the thermistor R __ or

NTC,

whose terminals are short-circuited, the potential at point A reaches its lowest value, while the potential at points B and C increases. The operational amplifiers 9 and 12 switch back to Η potential, so that the relay 10 is de-energized and the relay 13 has current flowing through it. The system is switched off. This state remains until the error is rectified and the switch-on lock is activated by pressing the pushbutton b1 has been solved.

In the event that the operational amplifier 9 fails or the contacts of the relay 10 weld together, the system will continue to operate continue until the maximum set temperature is reached and the set potential at point C of the voltage divider 3 is fallen below. As a result, the operational amplifier 12 switches to Η potential. The relay 13 has current flowing through it, the system is switched off. This state remains until the error has been rectified and the switch-on lock is activated the pushbutton b1 is released.

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To monitor the operational amplifier 12, its output is connected to the base of a transistor T ₀ via a resistor R _-_. The emitter-collector path of the transistor T ₂ is at the point N and via a resistor R _1g and the resistor R " _c " at the point P. In normal operation, the transistor is ι ο

T- is conductive through the offset voltage of the operational amplifier 12 and thus has no influence on the function of the safety switching unit 15. However, if the input of the operational amplifier 12 is short-circuited, no offset voltage occurs at its output. In this case, the transistor T ₂ blocks, so that the voltage applied to the Zener diode D _{1 via a diode D 0}

ο I

Voltage whose Zener voltage exceeds. This will make the thyristor THY1 is switched through, the relay 13 has current flowing through it and the system is switched off.

The voltage dividers 2 and 4 form a measuring bridge. The measuring bridge is balanced, i.e. the voltage between points D and E is zero if the following equation is true:

' ^r 7

^r 8
^{8 r} NTC ^{+ r} 7

If the temperature at the thermistor R »™« »changes, the measuring bridge becomes out of tune and the display instrument 7 has current flowing through it, i.e. the sensor temperature is displayed.

In order to achieve an exact switching of the operational amplifier 9 even with slowly occurring temperature changes, a feedback resistor R- is provided above the operational amplifier 9. This feedback also reduces the tendency to oscillate. The switching hysteresis is determined by the dimensioning of the circuit at about 2 ° C and can be varied _{by changing the feedback resistor R 17.}

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Further details of the circuit emerge from FIG. 3 and do not require any additional explanation.

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Claims (9)

Claims 1. Temperature control device with a temperature control unit, a safety switching unit and a temperature display, characterized in that a single temperature sensor (6) is provided, which is a thermistor (Rjj _TC ) and is connected to an electronic bridge circuit, that the electronic bridge circuit has two operational amplifiers (9 , 12) controls which are provided in the temperature control unit (11) and in the safety switching unit (15), and that the operational amplifiers (9, 12) actuate two oppositely switching switching units (10, 13). 2. Temperature control device according to claim 1, characterized in that the switching units are relays (10, 13), and that the relay (10) of the temperature control unit (11) closed current contacts and the relay (13) of the safety switching unit (15) has working current contacts. 3. Temperature control device according to claim 1 or 2, characterized in that the electronic Bridge circuit has at least three voltage dividers (1, 2,3), one of which contains the thermistor (Κ »™ ^). 4. Temperature control device according to claim 3, characterized in that the second voltage divider (2) the thermistor (R ^ jm / -.) Contains that the first and second voltage divider (1, 2) a first diagonal voltage bridge form for controlling the temperature control unit (11) and that the second and third voltage dividers (2, 3) have a second diagonal voltage bridge for controlling the safety switching unit (15) form. 5. Temperature control device according to claim 4, characterized in that the second voltage 709 & 4B / G61B - 13 ORIGINAL INSPECTED divider (2) and a fourth voltage divider (4) form a measuring bridge to which a display instrument (7) for the temperature connected. 6. Temperature control device according to one of the preceding claims, characterized in that between the thermistor (Rjjm, -.) ^{And the} operational amplifier (9, 12) a responsive to a thermistor breakage safety circuit (8) is provided. 7. Temperature control device according to claim 6, characterized in that the safety circuit (8) is provided between the center tap of the second voltage divider (2) and the operational amplifiers (9, 12). 8. Temperature control device according to one of the preceding Claims, characterized in that in the output of the operational amplifier (12) of the safety switching unit (15) a circuit for monitoring the operational amplifier (12) is provided. 9. Temperature control device according to one of claims 4 to 8, characterized in that in the first and third voltage divider (1, 3) jointly adjustable potentiometers (P _{3 1} , P _{3 2} ) are provided. 709 845/0615