WO2001079799A1

WO2001079799A1 - Analogue electronic thermostat

Info

Publication number: WO2001079799A1
Application number: PCT/CH2001/000230
Authority: WO
Inventors: Gaetano Scannapieco
Original assignee: Sate Safety Devices Technology Ag
Priority date: 2000-04-18
Filing date: 2001-04-10
Publication date: 2001-10-25
Also published as: AU4402701A

Abstract

The invention relates to an analogue electronic thermostat (1) comprising a desired value adjuster (9), a power supply, an output stage (11) comprising a relay, means (5) for intensifying the signal and means for creating (7) a switching command for said relay, said means being used to compare the desired value that has been set in the desired value adjuster (9) with the actual value that is supplied by a temperature sensor (3) which can be attached to the thermostat (1). According to the invention, the thermostat (1) has a range detector (6) which can be used to adjust a working range of the thermostat (1) independently of its desired value adjuster (9). In addition, a differential gap detector (8) which can be used to adjust the differential gap of the thermostat (1) independently of its working range is advantageously provided. The adjustability of the range detector (6) and differential gap detector (8) is obtained in an advantageous manner by the provision of isolating points in lines. The working range and the differential gap can be determined by the disconnection or connection of said isolating points. The invention also relates to a simple constant current source (4) for delivering a constant current. The temperature sensor (3) is operated using said current source.

Description

Analog electronic thermostat

The invention relates to an analog electronic thermostat of the type mentioned in the preamble of claim 1

Such thermostats are advantageously used in temperature controls of various types if a two-point control is desired. A setpoint is set on the thermostat, which is compared with an actual value measured by means of a temperature sensor. A switching command is generated from the difference between the setpoint and actual value

A thermostat of the type mentioned in the preamble of claim 1 is known from US-A-4,641,778. The switching point is adjustable, the switching hysteresis is determined as a function of the switching point. The switching hysteresis is increased with increasing temperature. This is not always useful when controlling a burner heated Boilers have very short burner runtimes when the load is low, which is unfavorable both for ecological reasons and because of the risk of corrosion for the boiler

It is also known (EP-A-0 942 271) to convert the signal of a temperature sensor according to a predetermined algorithm to temperature values. Although this makes it possible to use many types of temperature sensors, it also means a great deal of effort in the thermostat

From US-A-5,705,792 a digital thermostat is known in which the work area can be switched by means of a switch

From US-A-5,934,554 a room thermostat with a room temperature sensor is known, in which the switching point can be adjusted by means of a binary-coded switch. There is no range sensor independent of the setpoint adjuster

The above-mentioned thermostats serve very different purposes. There are also many other designs. A thermostat that is used in an oven, for example, cannot be used for a washing machine because the temperatures that can be set in an oven of over 100 degrees Celsius are not permissible in a washing machine The invention has for its object to provide a universally usable and at the same time simply constructed, but nevertheless precisely working thermostat that can be adapted to different areas of application. The simple structure should result in correspondingly low manufacturing costs

The stated object is achieved according to the invention by the features of claim 1. Advantageous further developments result from the dependent claims

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing

1 shows a block diagram of a thermostat,

2 shows a circuit diagram with details of a constant current source,

3 shows a circuit of a range adjuster,

Fig. 4 shows a circuit of a switching differential encoder

5 shows a circuit of a setpoint adjuster with associated driver and

6 shows a circuit of an output stage

In FIG. 1, the reference number 1 denotes a thermostat, to the input 2 of which a temperature sensor 3 can be connected. For precise temperature measurements, this is advantageously a so-called Pt-100 sensor, i.e. a sensor made of platinum wire with a nominal resistance of 100 ohms These sensors are characterized by the fact that there is a largely linear relationship between temperature and resistance. The temperature sensor 3 is a

Constant current source 4 supplied with voltage or current The constant current source 4 supplies a current that is independent of the resistance of the temperature sensor 3.This creates a voltage U at input 2, which is correlated with the resistance and thus with the temperature of the temperature sensor 3.This voltage becomes the non-inverting input of a Signal amplifier 5 supplied At the inverting input of this signal amplifier 5 there is a signal which is supplied by a range transmitter 6. The range transmitter 6 according to the invention can be used to set the temperature range for which the thermostat 1 is to be used. The range transmitter 6 delivers correspondingly an offset voltage to the signal amplifier 5, which also acts as a comparator. This is advantageously an operational amplifier of the type LM324 or LM358.

The output of the signal amplifier 5 leads to the inverting input of a comparator 7. The signal of a switching differential encoder 8 is present at the non-inverting input of the comparator 7. This in turn is connected to a setpoint adjuster 9, which in turn is controlled by a driver 10, i.e. is supplied with voltage. The comparator 7 is also advantageously an operational amplifier of the type LM324 or LM358.

An output stage 11 is controlled from the output of the comparator 7 and contains, for example, a relay, through whose contacts a load to be controlled is switched on and off. The output signal of the comparator 7 is also fed to the switching differential encoder 8. All elements of the thermostat 1 are supplied with operating energy by a voltage supply (not shown), this voltage supply being bipolar. One pole of which forms the reference potential GND, to which the temperature sensor 3 is also connected on one side. The other pole of the power supply supplies an operating voltage + U _B. With the thermostat 1 according to the invention, a double power supply with the operating voltages + UB and -ÜB, which is otherwise required to supply operational amplifiers, is not necessary, which reduces the outlay and thus saves costs.

The offset voltage supplied by the range transmitter 6, which will be shown later, at the same time determines which limits of the adjustable target temperature are possible by the target value adjuster 9. The setting values possible on the setpoint adjuster 9 are thus determined by the range transmitter 6. This makes it possible to adapt the thermostat 1 according to the invention to the limits which can be predetermined for different areas of use. Thereby, the thermostat 1 can be used for very different applications. For different applications with different temperature limits, therefore, only a single type of thermostat 1 has to be kept available. Since this thermostat 1 can thus also be mass-produced, lower production costs are incurred.

The switching differential encoder 8 can advantageously be used to separately adjust the size of the switching difference, which is also referred to as the switching hysteresis, ie the distance between the Switch-on and switch-off point should be. This in turn enables the applicability of the thermostat 1 according to the invention to be expanded, because the same type of thermostat 1 can therefore also be used if different switching differences are required for different areas of application

Both the range sensor 6 and the switching differential sensor 8 are advantageous so that the adjustment by the end customer of the device in which the thermostat 1 is used is not possible. The adjustment is only possible by the device manufacturer who purchases the thermostat 1, or of course possible by the manufacturer of the thermostat 1 This prevents unauthorized manipulation by the end customer, so that it is not possible, for example, to change the limit temperatures of 30 and 95 degrees Celsius, for example in a washing machine, specified for a specific application of the thermostat 1 happens in detail, will be described

In the following, advantageous configurations for individual components of the thermostat 1 are described in the order of their previous mention

FIG. 2 shows a circuit diagram in which the thermostat 1 according to the invention is shown with details of the constant current source 4. Here, + U _B denotes the positive pole of the voltage supply for operating the constant current source 4, with GND the common zero point, the reference potential Bipolar power supply is also available to the other elements of thermostat 1

The constant current source 4 advantageously contains two operational amplifiers, namely a first operational amplifier Vi and a second operational amplifier V _2. One of two resistors Ri, R ₂ is located at the non-inverting input of the first operational amplifier Vi, as is usually indicated by a "+" in the figure formed input voltage divider whose first resistor Ri is connected between the non-inverting input and the positive pole + U _{B of} the voltage supply, while a second resistor R ₂ lies between the non-inverting input and the reference potential GND. To this bipolar voltage source with the positive pole + U _B and the zero point GND, the two operational amplifiers Vi and V ₂ are also advantageously connected with their supply voltage connections, which is shown in the figures as An input voltage U _E , which is determined by the magnitude of the supply voltage Ü _B and the resistors Ri and R ₂ , is present at the non-inverting input. At the output of the first operational amplifier Ni, at which the output voltage U _OAI prevails, there is an output resistor R _{3 is} connected, the other connection of which is at an output 2 of the thermostat 1, to which, as shown in FIG. 2, the temperature sensor 3 can be connected. The output 2 carries an output voltage U _L. This arises from the fact that - what will be shown later - a constant current flowing through the temperature sensor 3 is generated by the constant current source 4, which produces a voltage drop at the temperature sensor 3 which represents this output voltage UL

There is another resistor between the output of the first operational amplifier Ni and the non-inverting input of the second operational amplifier N _2. Between the non-inverting input of the second operational amplifier V ₂ and the reference potential GΝD there is another resistor R _5. The two resistors R ₄ and R ₅ form thus a further voltage divider, namely that for the non-inverting input of the second operational amplifier V _2. Because, on the other hand, it acts as a voltage divider for the voltage U _aA i at the output of the first operational amplifier Ni, it is referred to here as an output voltage divider

Between the output 2 and the inverting input of the second operational amplifier V _{2 there} is another resistor R ₅ and between the inverting input of the second operational amplifier V ₂ and the output of the second operational amplifier V _{2 there} is another resistor R The output of the second operational amplifier V ₂ , which carries the voltage U _aA 2 is connected directly to the inverting input of the first operational amplifier Vi. The resistors R _Ö and R ₇ in turn form a voltage divider. Because it causes the feedback of the output voltage U _L to the two operational amplifiers Vi, V ₂ , it becomes referred to here as a feedback voltage divider

In the circuit according to the invention described above, the gain factor G _{V2 of} the second operational amplifier V _{2 is} calculated under the condition that the resistors R ₅ and R on the one hand and the resistors R ₄ and Rβ on the other hand are the same size, according to the following formula F1 G _y3 = - (Fl)

If the resistors 4 and R5 are now of the same size, the gain factor Gv _{2 of} the second operational amplifier V _{2 has} the value 1.

The output voltage U _{aA2 of} the second operational amplifier V ₂ results from the formula F2

U _M = {U _{βΛ -U} _L ) * G _vl (F2).

The output voltage of the first operational amplifier Vi results from the formula F3:

U _M = QJ _B - U _M ) * G _n (F3).

In this advantageous circuit, the gain factor Gvi is very large, with the result that a very small difference between the input voltage U _E and the output voltage _{aA2 of} the second operational amplifier V ₂ leads to a very large output voltage U _{OAI of} the first operational amplifier Ni. In itself, it would be greater than the input voltage U _E. But because then the output voltage aA2 would be greater than the input voltage U _E , the formula F3 would result in a negative value. An equilibrium is obtained when the input voltage U _E and the output voltage U _{aA2 are the} same. Taking formula F2 into account, it follows that (U _OAJ - U _L ) = U _E IG _V2 . In addition, I _L * R _{3 is} equal to UOAI - U _L , so that the product of output current I _L and resistance R _{3 is} equal to the quotient of input voltage U _E and gain factor Gv2. This results in the load current I _L according to the formula F4 as

I, = ^UE . (F4)

G * R

It is advantageously achieved that the load current II does not depend on the size of the temperature sensor 3. If the supply voltage U _{B has} the value 12 volts, the resistor Ri has the value 10 kOhm and the resistor R _{2 has} the value 2 kOhm, then the voltage U _E according to the formula F5

U _E = U * ^Rl (F5)

2 volts.

The load current I _{L is} calculated

If the resistor R _{3 has} the value 100 ohms, the load current is 20 mA. This current also flows through the load resistor R _L , even if the load resistor had the value zero. The maximum value of the load resistance may be around 300 ohms. Then namely the output voltage U _{OAI of} the first operational amplifier Vi according to the formula

8 volts, a value that is still portable with a supply voltage of 12 volts.

The resistors R », R ₅ , R« and R each advantageously have a value of 100 kOhm. The inexpensive types LM324 or LM358 are advantageously used as operational amplifiers Vi, V ₂ . If temperature sensors 3 with different resistance values are used on the thermostat 1, the dimensioning of the resistors must be adjusted accordingly.

A further resistor Rg is shown in the line leading to the inverting input of the operational amplifier Vi and another resistor R _{9 is shown} with dotted lines in the line leading to the non-inverting input of the operational amplifier Ni. With the help of these resistors R _g , R ₉ , an optimization of the input impedances at the two inputs of the operational amplifier Vj can advantageously be achieved. FIG. 3 shows a preferred, because advantageous, exemplary embodiment for the range transmitter 6. It consists of an operational amplifier V ₃₀ and a resistor chain connected to its non-inverting input. According to this exemplary embodiment, this resistor chain consists of five resistors R ₃₁ to R ₃ 5. The first the resistors of the chain, the resistor R ₃ ι is connected on the one hand to the operating voltage + U _B , on the other hand to the non-inverting input of the operational amplifier V _30. This is followed by a series connection of further resistors R ₃₂ , R ₃₃ , R ₃ and R ₃₅ from the connection points of the resistors R ₃₂ R ₃₃ , R ₃₃ R ₃ and R ₃₄ / R ₃ 5 and from the free end of the resistor R ₃ s each have a line connection to the reference potential GND. The resistor R ₃ ι on the one hand and the resistors R ₃₂ , R ₃₃ , R ₃ and R _35, on the other hand, thus form a voltage divider for the non-inverting input of the operator ionsverstärkers V ₃₀ With oblique crosses are three separation points T _A, T _B and T c is the connection lines are drawn at these locations interrupted to the reference potential GND, so the Widerstandsverhaltnis of said voltage divider and the voltage changes at the noninverting input of the operational amplifier V ₃₀

The inverting input of the operational amplifier V o ₃ is directly connected to its output and this leads to the inverting input of the Signalverstarkers 5 (Figure 1)

By appropriately dimensioning the resistors R ₃ ι, R ₃₂ , R ₃₃ , R ₃₄ and R ₃₅ and severing none, individual or all of the three separation points T _A , T _B and T _c , the resistance ratio of the voltage divider mentioned can be changed, thereby simultaneously the temperature range is determined, in which the thermostat 1 (Fig 1) can work. Since the change in the resistance ratio takes place by cutting through separating points T _A , T _B and T, this change can only be carried out once without corrective measures, so that the operation of Work area is definable

An example of such a design is given below. Resistor R ₃ ι has the value 47 kOhm, resistor R _{32 has} the value 1 kOhm, resistor R _{33 has} the value 156 kOhm, resistor R _{4 has} the value 210 kOhm and resistor R ₃₅ the value 82 Ohm Resistance values not included in the standard series are achieved by connecting two resistors in series, so the value 156 kOhm by

Series connection of 100 and 56 kOhm and the value 210 kOhm by series connection of 100 and 110 kOhm These exemplary resistance values result in the following working ranges for the thermostat 1 depending on the type of separation at the separation points T _A , T _B and T _c

If the line is not cut at any of the separation points T _A , T _B and T _c, the working range is from -10 degrees Celsius to +35 degrees Celsius.Thermostat 1 could be used for a combined heating and cooling device or for one in tropical countries Pure cooling device to be used

If the line is disconnected at the separation point T _A alone, a working range of 30 to 90 degrees Celsius results. Thereby the thermostat 1 could be used for a boiler or a boiler

If the lines are separated at the separation points T _A and T _B , a working range of 80 to 140 degrees Celsius results. Thereby the thermostat 1 could be used, for example, for an autoclave or a heating cabinet

If the lines are separated at all three disconnection points T _A , T _B and T _c , a working range of 100 to 200 degrees Celsius results. Thereby the thermostat 1 could be used, for example, for an air heating device or a sterilization device

The separation points T _A , T _B and T _c are cut either in the manufacturer's factory or at the manufacturer of devices such as boilers, autoclaves, etc. The work area is set using a type of mechanical programming.It is not accessible to the end user of the devices equipped with such thermostats 1

Inadmissible manipulations are therefore not possible, above all because, of course, the end user does not know the context

By using other resistance values, any work area can be realized with the same basic model of the thermostat 1. Because the same basic model of the thermostat 1 can be used for very different applications, it can be mass-produced with corresponding cost advantages. This is also a significant advantage with regard to warehousing at wholesalers

FIG. 4 shows an advantageous embodiment of the switching differential encoder 8. It has a further operational amplifier V ₄₀ , the output of which does not lead to inverting input of the comparator 7. A further resistor Rω is connected to the non-inverting input of the operational amplifier V ₄₀ , the other connection of which is connected to the reference potential GND. Another resistor R ^ is also connected, the other connection of which has a connection to the setpoint adjuster 9.

A further resistor R «is connected to the inverting input of the operational amplifier N ₀ , the other connection of which lies at the output of the operational amplifier Nω. Furthermore, a voltage divider formed from two further resistors R« and R _{4 is} connected to the inverting input of the operational amplifier V ₄ o second end connection to the operating voltage + U _B has between the connection point of the resistors R ^ / -w and the reference potential GΝD is a resistor array of four parallel resistors R «, ^, R» ₇ and R «arranged in each branch of the array of parallel resistors there is a separation point of the type already mentioned in connection with FIG. 3, which are denoted here by T _R , T _s , T _τ and Tu, in parallel with this parallel connection of the resistors

there is a transistor Trl, the emitter of which is connected to the reference potential GΝD and the collector of which is connected to the connection point of the resistors R ₃ / R ₄ / R ₄₅ / R ₄ 6 / R ₄₇ / R ₄ 8. The base connection of the transistor Trl leads to the output via a base resistor of the comparator 7 It is thus determined by the output of the comparator 7, whose state correlates with the position of the relay contained in the output stage 1 1, whether the transistor Trl is conductive or not. Accordingly, it is determined whether the array of the

Parallel resistors R ₅ / R 6 / R ₇ / R ₄ 8 are effective or not. This has a corresponding effect on the voltage at the inverting input of the operational amplifier V ₀

As mentioned in the area sensor 6 (FIG. 3), the separating points T _R , T _S , T _T and Tu are used for setting, in this case for setting the switching differential of the thermostat 1

Depending on which of the separation points T _R , T _s , T _τ and Tu is interrupted, there is a different switching difference of the thermostat 1 If the conductor tracks at the separation points T _s , T _τ and Tu are interrupted, only the resistance of the resistor array is present _t5 effective If the conductor tracks are interrupted at the separation points T _R , T _τ and Tu, then only the resistor R4 _{6 is} effective. In the same way, only the resistors π and _{t8 are} effective when the separation points T _R , T _s and Tu or T _R , T _s and T _{τ are} interrupted since the change in the resistance ratio by If separation points T _R , T _s , T _τ and Tu are cut, this change can only be carried out once without corrective measures, so that the switching difference can be determined by this operation

A dimensioning example is given below. The resistor R-1 ₅ has the value 5.93 MOhm and, because a corresponding standard value does not exist, is formed by a series connection of resistors with 5.6 MOhm and 330 kOhm. The resistor t6 has the value 2, 94 MOhm, composed of 2.7 MOhm and 240 kOhm, the resistor * ₇ the value 1.5 MOhm, formed from 1 MOhm and 500 kOhm, and the resistor R _4g the value 700 kOhm, formed from 500 kOhm and 200 kOhm

If only the resistor R _{45 is} effective, which is the case when the disconnection points Ts, T _τ and Tu are interrupted, the switching difference of the thermostat 1 is 0.5 degrees Celsius. If only the resistor R 6 is effective, the switching difference is 1 degree Celsius. When the resistors R-π or R _{48 are} effective, there is a switching difference of 2 degrees Celsius or 4 degrees Celsius

By choosing the size of the resistors and by corresponding interruptions of separation points, the switching differences of the thermostat 1 can be designed within wide limits in the above-mentioned embodiment, it is provided that three of the separation points T _R , T _S , T _T and Tu are always separated it is also possible to measure the individual resistances R «, R«, R » ₇ , Ris in such a way that none, one, two or three of the separation points T _R , T _s , T _τ and Tu are separated. This allows the number of possible ones Significantly increase the settings of the switching differential

Thus, the thermostat 1 can advantageously be adapted to any task with regard to the switching difference.This adaptation is also carried out, for example, in the factory or at the manufacturer of devices in which the thermostat 1 according to the invention is used. Thus, the switching user is also inadmissible manipulations by the end user the device is not possible

For the sake of completeness, the dimensioning of the other resistors is also mentioned. The resistors R-to, Rn, R «, R ₄₃ and Rj ₄ each have a value of 100 kOhm, the base resistance« has a value of 10 kOhm. The operational amplifier V ₀ is from same type as the operational amplifiers Vi and V ₂ (FIG. 2) and the transistor Trl is for example of the PMBT2222 type

Figure 5 shows an advantageous circuit of the setpoint adjuster 9, with an associated driver 10, the driver 10 contains a further operational amplifier V ₅ o, which is the same type as all other operational amplifier of the thermostat 1 the non-inverting input of a voltage divider in turn is arranged, consisting of two there are further resistors R ₅₀ and R ₅ 1. The resistor R ₅₀ is connected to the operating voltage + U _B on the one hand, and to the non-inverting input on the other hand. The further resistor R51 is arranged between the reference potential GND and the non-inverting input. Both resistors R50 and R ₅₁ have, for example the value 100 kOhm. The inverting input of the operational amplifier V50 is connected via a further resistor Rs ₂ to the output of the operational amplifier V ₅₀ , this output being connected on the other hand to one connection of the setpoint adjuster 9. Advantageously, it is located at the inverting input of the operational amplifier kers V ₅₀ another resistor Rs ₃ , which is connected on the other hand to the reference potential GND. The resistor R ₅₃ has, for example, a value of 150 kOhm. In one of the connecting lines to the resistor Rs _{3 there} is again a separation point, which here has the designation T _z . This is advantageous because this resistor Rs ₃ and the separation point T _z one optimal effect of the setpoint adjuster 9 can be achieved if the range transmitter 6 has different configurations, as has been described in connection with FIG. 3. In order to achieve the optimal effect of the setpoint adjuster 9, it is expedient to interrupt the line at the separation point Tz , If the first three working ranges, namely -10 to 35 degrees Celsius, 30 to 90 degrees Celsius or 80 to 140 degrees Celsius on the range sensor 6 have been set by separating or not separating the corresponding separation points T _A , T _B and T _c advantageous that the resistor R _{53 is} only effective when the working range 100 to 200 on the range sensor 6 Degrees Celsius has been set

The setpoint adjuster 9 is a potentiometer of, for example, 50 kOhm resistance value and advantageously has a linear characteristic. As can already be seen from FIGS. 2 and 4, the tap of the setpoint adjuster 9 leads to the switching differential encoder 8 FIG. 6 shows the circuit of an advantageous embodiment of the output stage 11. The output stage 11 is driven by the output of the comparator 7. This signal passes through a base resistor Rβo to the base of a switching transistor Tr2, whose emitter is at the reference potential GND. An output relay Rel is connected to its collector, the second connection of which is connected to the operating voltage + U _B via a series resistor Rβi. As is generally the case, a protective diode D is connected in parallel to the coil of the output relay Rel. In addition, between the connection of the series resistor Rπ and the coil of the relay Rel there is a capacitor C, the function of which is to protect the relay Rel from an unwanted drop caused by voltage fluctuations.

Reference number G denotes the connection for a device to be controlled by the thermostat (1), which is switched on, off or switched over by the contacts of the relay Rel.

In addition, an additional circuit consisting of a further transistor Tr3, its base resistance R _ό2 , a further operational amplifier Vβo and further resistors Rό ₃ , R _Ö and Rβs can advantageously be connected to the base of the switching transistor Tr2. The resistors Rβ ₃ and Rβ form a voltage divider for the non-inverting input of the operational amplifier V _ÖO , the voltage divider being on the one hand at the operating voltage + U _B and on the other hand at the reference potential GND. Both resistors have a value of 100 kOhm, for example, so that a voltage equal to half the operating voltage + U _B is present at the non-inverting input of the operational amplifier V ₆ o, ie 6 volts at an operating voltage + U _B of 12 volts. The inverting input of the operational amplifier V ₆ o is connected via the resistor R ^ to the input 2 of the thermostat 1 (Fig. 1), so it carries the voltage U _L , which prevails over the temperature sensor 3 (Fig. 1). If the temperature sensor 3 by a

If the interruption is defective or not connected at all, this additional circuit ensures that the output relay Rel drops out. The switching transistor Tr2 and the transistor Tr3 are, like the aforementioned transistor Trl (FIG. 4), of the PBMT2222 type. The resistance Rβs has, for example, a value of 10 kOhm, the base resistance Reo 6.8 kOhm and the series resistor Rβi 620 Ohm. The latter limits the charging current for capacitor C, which has a capacitance of 47 μF, for example. Type 1N4148 can be used as diode D. The function of the thermostat 1 will now be briefly explained again. The signal amplifier 5 amplifies the voltage signal generated by the temperature sensor 3 on the basis of the constant current, the offset voltage generated by the range transmitter 6 being taken into account at the same time. The output of the signal amplifier 5 thus supplies a signal relating to the working range set in the range transmitter 6 to the comparator 7. This signal is linked by the comparator 7 to the switching state of the output stage 11. The comparator 7 is thus responsible for the switching hysteresis becoming effective, the size of the switching hysteresis being determined by the setting of the switching differential encoder 8.

The aforementioned types and dimensions of the components are only to be understood as examples and relate to the use of a Pt-100 sensor as a temperature sensor 3. Instead of this, other sensor types can also be used in connection with the thermostat 1 described, for example Pt-1000 Sensors, but also NTC resistors. In such cases, modifications to the dimensioning of the components may be indicated or necessary.

The thermostat 1 described above is of simple construction, requires only a bipolar voltage supply, advantageously 12 volts direct current, and consists of common, very inexpensive components. All operational amplifiers are advantageously of the same type, namely LM324 or LM358. Since a component of these types contains four operational amplifiers, only two such components are required, since the overall circuit of the thermostat 1 has eight operational amplifiers.

Despite the simple construction, the thermostat 1 according to the invention is very precise and very flexible with regard to its applicability, because the working range is adjustable and the switching difference can also be selected independently of it.

Claims

claims

1 analog electronic thermostat (1) with a setpoint adjuster (9), a voltage supply, an output stage (11) with a relay (Rel), means (5) for signal amplification and means (7) for forming a switching command for the relay (Rel) with which the setpoint set on the setpoint adjuster (9) and that of an am

Thermostat (1) connectable actual temperature sensor (3) is compared, characterized in that the thermostat (1) has a range transmitter (6) with which a working range of the thermostat (1) can be set independently of its setpoint adjuster (9)

2 Thermostat according to claim 1, characterized in that the area sensor (6) from an operational amplifier (V ₃₀ ) and one of its inputs connected to a voltage divider forming resistor chain (R ₃ ι, R ₃₂ , R ₃₃ , R ₃₄ , R ₃ s), whereby one line connection leads from the connection points of the resistors (R ₃₂ / R ₃₃ , R ₃₃ / R ₃ , R ₃₄ / R ₃₅ ) and from the free end of the last resistor (R ₃ s) to a reference potential GND, that separating points (T _A , T _B , T _c ) are arranged in these connecting lines, the resistance ratio of the voltage divider and thus the working range being able to be determined by cutting through none, individual or all separating points (T _A , T _B , T _C )

3 Thermostat according to claim 1 or 2, characterized in that the thermostat (1) has a switching differential generator (8) with which the switching differential of the thermostat (1) can be set independently of its working range

4 Thermostat according to claim 3, characterized in that the switching differential encoder (8) has an operational amplifier (V ₄ o) and a resistor array connected to one of its inputs (R ₄₅ , t ₆ , R_ι ₇ , ts) that in each of the branches of Resistance arrays (R ^, 6, -, R-ts) a separation point (T _R , T _s , T _τ , Tu) is arranged, the switching difference by separating the separation points (T _R , T _s , T _τ , Tu) of the thermostat can be determined

5 Thermostat according to one of claims 1 to 4, characterized in that the setpoint adjuster (9) is a potentiometer which is connected to a driver (10), the driver having an operational amplifier (V ₅₀ ), at whose one input in a connecting line to a further resistor (Rs ₃ ) is arranged a separation point (Tz), the effect of the setpoint adjuster (9) being able to be influenced by cutting through the separation point (T _z )

6. Thermostat according to one of claims 1 to 5, characterized in that the thermostat (1) connectable temperature sensor (3) is fed from a constant current source (4), said constant current source (4) with the same bipolar supply voltage with a positive Pol (+ U _B ) and the common reference potential (GND) is operated with which the other circuit parts of the thermostat (1) are operated, that it has two operational amplifiers (Vi, N ₂ ) that by means of a to the supply voltage (+ U _B ) connected

Input circuit (Ri, R ₂ ) an input voltage (U _E ) can be generated, which is fed to the non-inverting input of the first operational amplifier (Vi), that the output of the first operational amplifier (Vi) via an output resistor (R ₃ ) with the output ( 2), to which the temperature sensor (3) can be connected, that the output of the first operational amplifier (Vi) is connected to the common reference potential (GΝD) via an output voltage divider, which is formed from further resistors (R ^ R ₅ ) , wherein the circuit point between its two resistors (i, R ₅ ) is connected to the non-inverting input of the second operational amplifier (V ₂ ), that the output (2) of the constant current source (4) via a feedback voltage divider, which consists of further resistors (Rβ, R ₇ ) is formed, is connected to the output of the second operational amplifier (V ₂ ), the switching point between the two resistors anden (Rβ, R ₇ ) is connected to the inverting input of the second operational amplifier (V ₂ ), and that the output of the second operational amplifier (V ₂ ) is connected directly to the inverting input of the first operational amplifier (Vi)