DE2518760A1 - Proportional controller with square wave output - Schmitt trigger with capacitor diode circuit operates as multivibrator with frequency fixed by error current - Google Patents

Abstract

A proportional controller particularly suited to temperature regulating applications using current generating sensors and input devices, provides an output control action in the form of cyclic switching with the frequency proportional to the error. The measured parameter is provided by a sensor (14) coupled to the positive terminal (12) and the reference device (15) is coupled to the negative terminal (13). The common point (17) is coupled to a Schmitt trigger circuit (18) that generates a square wave frequency output dependent upon the current difference and the characteristics of a diode (20) and capacitor (13). A relay (21) is switched to control a heating element (22). When the measured output is considerably less than the reference the relay is held in a fully switched condition.

Description

P-control device The invention relates to a P-control device. All such devices have in common that a target / actual value comparison or an actual / actual value comparison in regulation or control based on measured value differences must be made. In known circuits, this comparison is varied Species carried out. The target and actual values are first turned into electronic signals created, which are compared with each other in a further stage.

tigdbe of the invention is to create a P-control device, when converting the target / actual value into an electronic signal a comparison value will be obtained.

According to the invention, this object is achieved in that the P-control device contains two series-connected power generators, at least one of which accordingly the controlled variable is changeable, and that between the power generators on the current difference there is responsive switching element connected.

The switching element can advantageously be parallel to one of the current generators be connected and according to a further preferred embodiment of the invention from a Schmitt trigger, a thyristor or a similar component and one there are capacitors connected in parallel.

The setpoint and actual value sensors are parts of known power generators. One of the power generators is connected to a bollard circuit and the other Power generator has reverse polarity and is connected to the other pole of the circuit tied together. At the junction of the two power generators connected in series there is a very steep transition of the voltage, but the internal resistance becomes of this current generator combination correspond to the respective measured value deviation. A two-point controller can be set up with the voltage evaluation. Get this one The evaluator, i.e. the switching element, has a finitely high input resistance use this to use the difference between the switching value and the P control.

In order to prevent the switching element from reversing the voltage applied to it protect, a diode can preferably be provided. Such a reversal can occur when, for example, the temperature control despite high temperature Setpoint is downwardly controlled.

The maximum current consumption of the switching element can preferably be lower than the maximum differential current between the current generators. This creates an area in which the switching element no longer responds and therefore no implementation the set-actual value difference in a pulse train, for example successive Switch-on and switch-off pulses, more takes place, i.e. an area full of power.

Further advantages and features of the invention emerge from the description in connection with the drawing.

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

1 shows a schematic circuit diagram of the control device according to the invention and FIG. 2 is a circuit diagram of an exemplary embodiment.

The P control device 11 shown in Fig. 1 has two in series Current generators 14, 15 connected between Bingangsdnschldsse 12, 13 Current generators can be known circuits that provide a constant Generate electricity largely independent of external resistance or voltage, d. H. to power sources with practically infinite internal resistance.

The current generator 14 is dependent on the actual value of the control circuit changes. To do this, he can use a measurement sensor, such as an NTC resistor, included, the current flowing through the generator is proportional to the Controlled variable, i.e. the value to be controlled, changed.

The current generator 15 is in the example shown according to Target value adjustable. For example, it can contain a potentiometer, on which the user of the circuit can set a desired temperature. It however, it is also possible to leave the current generator 15 permanently set, if if this is desired, or to have it controlled by a second measuring sensor, see above that for example a regulation or control as a function of a temperature difference he follows.

In parallel with the power generator 15, i. H. at connection point 17 between the two power generators 14 and 15 and the negative line from connection 13, a switching element 16 is connected. The switching element exists in the exemplary embodiment from a parallel connection of a known Schmitt trigger 18 and a capacitance 19. A diode 20 is connected to bridge the capacitor. The Schmitt trigger 18 actuates a switching relay 21, which switches the current to a heating resistor 22. The control loop is closed by the fact that the heating resistor is connected to the power generator 14 associated temperature sensor.

The P control device according to FIG. 1 operates as follows: The Schmitt trigger When switched off, 18 has high resistance in its input values. He locks below its response voltage practically the equalizing current that leads to the connection point 17 flows in order to compensate for the current difference, that of the target / actual value difference is equivalent to. This charges the capacitor 19 and generates a charging voltage, which increases slowly until it reaches the ignition voltage of the Schmitt trigger 18 has and now through this. As a result, the relay 21 is switched on on the one hand and on the other hand, the Schmitt trigger has low resistance in its input values. if the current consumption of the Schmitt trigger is greater than the differential current, so discharges the capacitor 19 via the Schmitt trigger 18. This causes the voltage to drop off again and the Schmitt trigger switches when its lower switching threshold is reached out again. This game repeats itself, so that a pulse frequency is generated, that of the difference between the two currents from the current generators 14 and 15 and thus the Corresponds to the target / actual value difference. The controller clocks the heating resistor added power.

If the target and actual values are further apart, so is that Current difference between the two current generators is greater. Will this current difference greater than the input current of the Schmitt trigger 1d, then the capacity is charged 19 to its maximum value, so that the voltage at the Schmitt trigger remains higher than its lower threshold. There is then no more clocking. Through this an area is created in which, for example, the heating resistor 22 has full power is fed.

This is desirable while a heater is heating up.

The size of this hundred percent area can be, for example, by a change in resistance in the EiricrSinift trigger or the switching element 16 is set will. Only when the differential current is less than the current consumption of the Schmitt trigger, which is determined by its internal resistance, the clocking starts again.

The diode 20 bridging the capacitor ensures that the reverse Current difference no damage occurs.

The switching element 16 is then short-circuited.

The regulator according to the invention can be very easily varied Conditions to be adjusted. While in the example shown, it works as a temperature controller is designed for controlling a heater, it can be used as a controller for refrigeration devices can be easily adjusted by the fact that the current generators 14 and 15 against each other be swapped.

The characteristics of the sensors used can also be changed in this way must be taken into account. If you have the flowing over the two power generators If the current is very large and the one current of the Schmitt trigger is small, then one can carry out a fine adjustment.

In Fig. 2 is an embodiment of the regulating or control device which is used to control an AC motor 25. The circuit is connected to the normal alternating current network via input connections 12a, 13a. In the The circuit shown in detail in FIG. 2 includes two current generators 14a, 15a, which are located in a measuring circuit part formed from a measuring bridge 26. In the exemplary embodiment, each current generator consists of a transistor 27, 28, which is connected in series with one measuring sensor 29, 30 each. The sensors 29, 30 are the present example temperature-dependent measuring resistors, for example NTC or PTC resistors. When using two sensors in both power generators, i.e. on both sides of the measuring bridge there is a control device that is dependent on from a difference value between the two measuring sensors 29, 30 regulates, for example operates a consumer depending on the difference temperature. For many However, one of the two measuring sensors can be used with an adjustable Component, for example a setting potentiometer, be replaced, which then has a The setpoint specifies, while the measuring sensor located in the other branch of the measuring bridge determines the actual value. The arrangement of the setting device and measuring sensor in the The measuring bridge depends on its characteristics and the size to be controlled (heating or cooling control etc.). If the setpoint is a fixed value, a Branch of the measuring bridge, a fixed component can also be used.

The base of the transistors 27, 28 is connected to a voltage divider, which consists of three resistors 31, 32, 33, the parallel to that the branch containing the two sensors 29, 30 and transistors 27 and ad is located. The base of the transistor a7 is between the resistors 31 and 32 and the base of the transistor ad between the resistors 32, 33 is connected.

The current generator 14a is connected to a connection branch 47, the supplied from the input terminal 12a via a resistor 34 and a diode 35 will. The current generator 15a is connected to a connection branch 44 which is connected via a rectifier bridge 36 with four diodes and an interference suppression capacitor 37 is connected to the connection 13a.

The corner point 38 of the rectifier bridge connected to the input connection 13a is with the interposition of the interference suppression capacitor 37 with one pole of the motor 25 connected corner point 39 opposite, while the other pole of the motor has a Resistance is applied to the AC input terminal 12a. The negative corner point 40 of the rectifier bridge is connected directly to the connection branch 44, while the positive corner point 41 via a resistor 42 and a power thyristor 43 is placed on this connection branch 44.

A Zener diode 45 is connected in parallel with the measuring bridge 26.

A diode 46 supplies the side facing the connection branch 47 a voltage divider formed by resistors 48, 49. In parallel with the voltage divider an electrolytic capacitor 50 is connected.

A switching element 16 contains a capacitor 51, which on the one hand the connection branch 44 and on the other hand via a diode 52 to the connection point 17 of the measuring bridge, which lies between the two collectors of the transistors, is placed is. The capacitor 51 is connected via a resistor 53 a thyristor 54, whose ignition electrode is connected to the voltage divider point 55 of the voltage divider 48, 49 is connected, which in turn via a diode 56 with the thyristor-side Terminal of the capacitor 51 is connected.

The base of the thyristor 54 is connected to the collector of a transistor 57 connected, the emitter of which is connected to the connection branch 44. The basis of the Transistor 57 lies between two resistors forming a voltage divider 58, 59, which are connected in parallel with the power thyristor 43.

A resistor 60 is connected in parallel with the transistor 57. The collector of transistor 57 is connected to ignition electrode 61 of power thyristor 43.

The circuit described works as follows: As already mentioned, the power is supplied directly from the AC network. The diode 35 provides that the current generators 14a, 15a only during the positive half-wave of the Network AC work. The Zener diode 45 limits the voltage in the measuring circuit part in that it is responsible for the difference voltage lying above its limit voltage becomes conductive. A positive trapezoidal voltage is thus generated, which is in the low voltage range so that in the majority of the circuit simple and cheap components can be used.

Resistor 32 ensures equal currents through resistors 31 and 33, so that at the base of transistors 27 and 28 the same ratios, however with reversed polarity. Depending on the one at the connection point 17 present differential current of the two current generators 14a, 15a becomes the capacitor 51 across the diode 52, charging the capacitor with reverse polarity prevented and thus fulfills the same function as the diode aO in Fig. 1, charged because the thyristor 54 is blocked. Via the diode 46, the Voltage divider 48, 49 and the diode 56 is used for a certain minimum charge of the Capacitor C2 taken care of. Due to the current flow through the diode 52, in the capacitor 51 as a function of the current difference (and thus the difference of the two measured values of the measuring sensors 29, 30) a step-shaped voltage increase, which increases during every positive half-cycle until the trigger voltage of the thyristor 54 is reached and the capacitor 51 passes through the resistor 43 through the thyristor 54 discharges. The resistor 43 together with the capacitor 51 forms a timing element and prevents the capacitor from discharging too quickly.

During the positive half cycle, the current from the thyristor 54 flow through the transistor 57, since this through the resistors 42 and 58 to the Rectifier bridge 36 is connected to the line voltage and during each positive half-wave is switched through and thus conductive.

During the zero crossing of the voltage in the relevant branch, i.e. also at the power thyristor 43, the transistor 57 turns off and the current from the capacitor 51 flows through the thyristor 54 as ignition current to the ignition electrode 61 of the power thyristor 43, so that it is ignited and thus becomes conductive. At the subsequent voltage rise of the alternating current at the rectifier bridge 36 a rectified current flows from the input connection 13a via the rectifier bridge via the resistor 42 and the thyristor 43 and via the rectifier bridge to Motor 35 so that it is supplied with power. As a result of the current flow through the thyristor 43 this holds itself and does not cause a voltage increase forth that the transistor 57 a required for switching on Could supply base voltage. This therefore remains blocked and the ignition current flows as long as the ignition electrode 61, as the capacitor 51 is still charged.

The thyristor 43 is triggered for the reasons described always at the beginning of the negative half-wave, so that the first let through and to the Motor 25 conducted half-wave is the negative half-wave. The time constant that is from the dimensioning of the capacitor 51 and the resistor 53 is selected so that the zero crossing of the ignition current at 61 due to the discharge of the capacitor 51 only during the second half-wave that has passed, i.e.

the positive half-wave takes place. This ensures that too this second half-wave still comes to motor 25 and is fully driven through. After this The thyristor 43 becomes the second, i.e. positive half-cycle as a result of the zero crossing of the current flowing through it, which also forms its holding current, is deleted and thus locking. Since the shutdown of the thyristor due to the lack of holding current always at the end of the second half-wave and naturally never in between the tolerance in the time constant and thus in the dimensioning of the components 51, 53 be very large, since the zero crossing of the capacitor current sometime between the beginning and the end of the second half-wave can take place. The discharge time can be somewhere between ten and twenty milliseconds.

The electrolytic capacitor 50 is used to smooth the ignition circuit for the thyristor 54.

It can therefore be seen that a Type of intermittent regulation is created in which entire alternating current periods are always supplied which are then followed by a pause of one or more (integer) alternating current periods separated are. As a result, the consumer contains pure alternating current without direct current components, which would occur if incomplete, for example half, alternating current periods would be fed. These cause braking and braking, especially in motors thus lead to poor efficiency and increased engine temperatures. It will a stepless regulation of AC consumers, and in particular AC motors created that works continuously from zero to maximum performance. The top performance is reached when the current difference at connection point 17 is so great that that there is no longer a complete discharge of the capacitor C2 and thus an ignition current is always available for the thyristor 43. The motor 25 works then at full power.

For motors and other not very slow alternating current consumers, like magnets etc., it will be desirable if the pulse duration and therefore also the duration of the pause is as short as possible, i.e. if possible in the lower control range nu is one alternating current period. It is when this is not so important, however the time constant embodied by the capacitor 51 and the resistor 53 is also possible to be chosen so large that two or more alternating current periods are always allowed through will. It is also possible, if direct current components are not important, to use the Omit the rectifier bridge 36, which ensures that the transistor 57 a certain half-wave can always be defined as the beginning. In this case it would then be possible to work with individual half-waves, which is the pulse duration still shortened, but creates direct current components.

Above all, however, the equilibrium judge bridge ensures that with only one power thyristor 43 can be worked, which for the symmetry of the supplied AC voltage is important is because the otherwise necessary two thyristors could never be absolutely the same and especially the same ignition and have holding currents.

The device described above corresponds in its basic structure that of FIG. 1 with the difference that instead of the Schmitt trigger described there the thyristor 54 is used, the switching thresholds once the ignition voltage and on the other hand are the holding current.

It is also important that the regulation is largely free of radio interference works because the thyristor 43 always switches when the current passes through zero. Therefore the circuit works absolutely trouble-free with an ohmic load. When a phase shift is present, a voltage jump occurs when switching. You can do this, however, because no power is switched on with a relatively small interference suppression capacitor Intercept 37.

AC motors, for example Shaded pole motors to control with the device.

Despite constant switching on and off, the speed remains constant in that at low speed a switching of a period length a The increase in speed is greater than in the higher speed range. That’s in the area slower speed, the deceleration time is longer, so that a slightly fluctuating, but results in essentially constant speed. Especially with engines with long Start-up time that drive a part of a large centrifugal mass, such as fan motors, the uniformity is fully satisfactory. The control device is particularly advantageous Can be used in connection with heating and ventilation, for example for fan motors of storage heaters, in which the discharge is regulated by the fans, for Controlled ventilation of interiors and for circulation pumps from Central heating. With the infinitely variable control, a very high level of control accuracy can be achieved can be achieved, which benefits energy consumption. For example, the Discharge control of a storage heater the device can be built so that already lowering the room temperature by 0.1 ° brings the motors to full speed and gives a fraction of this temperature to release a partial power. the The damping of the control loop is taken over by the inertia of the measuring resistor. This should therefore have a certain thermal inertia.

It is also possible to use other consumers than AC motors to regulate or control the facility.

For example, a strongly damped solenoid valve could be reyeled, for example to use this as a function of the temperature measurement of a measuring resistor to regulate the output temperature for hot water. Such an electronically regulated one Mixer faucet could temperature hot water to a fraction of a degree output. The advantages of the setup, especially switching at zero power and the lack of direct current components in the withdrawal from the alternating current network also offers advantages for other consumers, for example with purely ohmic ones Consumers, such as heating resistors, since there are rail current components due to network contamination are not allowed.

Another area of application is the most precise control of heating, for example for laboratory equipment etc. It can be seen that instead of the measuring resistors for temperature measurement also other measuring sensors, for example photo sensors or humidity measuring devices can be used to regulate the corresponding quantities.

Another advantage is the particularly high degree of reinforcement of the Device according to the invention that makes it possible power, with the smallest Control deviations, for example at fractions of degrees, infinitely inform the consumer to regulate from zero to one hundred percent.

It can also be seen that the fact that in the invention Mainly components for low voltage can be used, an essential Simplification of the structure results. Only the rectifier bridge 36, the resistor 42 and the power thyristor and the line voltage side of the diode 35 Components must be designed for mains voltage, while the other components without the need for a special voltage converter designed for low voltage can be.

Claims (17)

Expectations 0 P control device, characterized in that it has two in series switched current generators (14, 14a, 15, 15a), of which at least one (14a, 15a) can be changed according to the controlled variable, and that between the current generators (14, 14a, 15, 15a) a switching element that responds to the current difference present there (16) is connected. 2. P-control device according to claim 1, characterized in that the switching element (16) connected in parallel to one of the current generators (15, 15a) is. 3. P-control device according to claim 1 or 2, characterized in that that the switching element (16) is a function of the voltage at a switching element (54) of the time and the differential current increasing capacity (51) has. 4. P-Regeleinrichtuny according to one of the preceding claims, characterized characterized in that a diode (20, 52) to protect the switching element (16) against Polarity reversal is present. 5. P-control device according to one of the preceding claims, characterized characterized in that the maximum power consumption of the Scnaltelementes (16) is lower is than the maximum differential current between the current generators (14, 14a, 15, 15a). 6. P-control device according to one of claims 3 to 5, characterized in that that the switching element (18) is a circuit that acts like a Schmitt trigger. 7. P-Regeleinricntung according to one of claims 3 to 5, characterized in that that the switching element (54) is a component acting like a thyristor. d. P-control device according to one of the preceding claims, characterized characterized that for regulating or controlling electrical AC consumers (25) the device (11) the consumer the performance in short power pulses of half or whole alternating current periods or multiples thereof. 9. P-control device according to claim 8, characterized in that the device (11) to the consumer (25) always integer alternating current periods feeds. 10. P-control device according to one of the preceding claims, characterized gekennzeictmet that the majority of them are designed for extra-low voltage Device (11) equipped with components without voltage conversion to the alternating current network connected and through a Zener diode (45) or an identically acting component the low voltage is limited. 11. P-control device according to one of claims 8 to 10, characterized characterized in that the capacitance (51) is connected to the ignition electrode via the switching element (54) (61) of a power thyristor (43) or a similarly acting component is. 12. Device according to one of claims 3 to 11, characterized gekennzeicnnet, that the discharge of the capacitance (19, 54) takes place in a predetermined time. 13. Device according to claim 12, characterized in that the Capacity (54) discharge time constant longer than a half and is shorter than a full AC period. 14. Einrictuny according to one of claims 11 to 13, characterized in that that an electronic voltage dependent on the voltage applied to the power thyristor (43) Switching element (57) applies the ignition voltage for the power thyristor (43) to the ignition electrode (61) can only take effect when the voltage passes through zero. 15. Device according to claim 14, characterized in that the vass Switching element (57) is a transistor diverting the discharge current of the capacitance (51) is. Ib. Device according to one of the preceding claims, characterized in that that a diode (35) is present, which the Messchaltunysteil (26) in each case only during a half-wave of the alternating voltage. 17. Device according to one of the preceding claims, characterized in that that the current generators (14a, 15a) each have a measuring or setting resistor (29, 30) and an electronic one connected in series, acting like a transistor Has component (27, 28) whose base has a parallel to the measuring or setting resistor (29, 30) lying voltage divider (31, 32, 33) is connected.