RU2359309C2 - Device for regulating temperature of object - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: present invention relates to electrical engineering, electronics and heat engineering. The device for regulating temperature of an object contains power supply circuits connected to each other, series-connected temperature sensor, amplifier, connected to the second power supply circuit, and a transistor, the output of which together with the first power supply circuit forms the output of the device for connecting to a heater. The device also contains series-connected second temperature sensor, second amplifier, connected to the third power supply circuit, and a current generator, the output of which is connected in series with the above mentioned transistor and connected to the common power supply circuit of the device. The first and second temperature sensors, transistor and current generator can minimise transient thermal impedance relative the object, on which the device is fitted.

EFFECT: increased reliability through elimination of probability of heating whenever there is a fault in the device, and increased functional capabilities of the device due to provision for combining the role of temperature regulator and heater without lowering reliability of the executed function.

3 cl, 1 dwg

Description

A device for stabilizing the temperature of a product belongs to the fields of electrical engineering, electronics, and heat engineering and can be used for its intended purpose, namely, to automatically heat and maintain the temperature of elements, structural parts, electronics, temperature in microthermostats, temperature fields of various extended objects, etc. .P. in situations where the temperature of the product must exceed the ambient temperature.

A known temperature stabilizer using bimetallic plates with contacts that open when the desired temperature is reached, is used, for example, in irons.

However, such a temperature stabilizer has a small service life and low accuracy of temperature maintenance.

Known devices for stabilization (regulation) of the temperature of the product, containing temperature controllers, temperature sensors, amplifiers, actuators and heaters from very complex [1] to very simple [2].

Despite the significant difference in the performance of these devices, they have a reduced reliability and they require heaters directly to stabilize the temperature. Moreover, in such devices, the placement of temperature sensors, heaters and regulators close to each other is usually difficult. Due to this, an error appears in determining the temperature, a delay in the temperature stabilization circuit, and overheating is possible. In addition, these devices are unreliable in principle: parts may be defective, which will lead to the inability to turn the heater on and off, and temperature-stabilized equipment may fail. And with a short circuit in the heater, the device itself may fail, damage the power source. In this regard, such devices for stabilizing the temperature of a product cannot be used for their intended purpose in especially critical systems, for example, as part of spacecraft, or for maintaining reagents in specified limits within complex technological processes.

The closest in execution (prototype) can be recognized as one of the mentioned devices [2], containing power circuits connected in series to a temperature sensor, an amplifier connected to a power circuit, and a transistor, while the output of the transistor forms the output of the device for connecting the heater. The role of the temperature setter in the prototype is performed by the amplifier of the device, made in the form of a Schmidt trigger and having a response threshold and a release threshold for the input voltage. These thresholds with respect to the signals from the temperature sensor correspond to the range of temperature stabilization of the product. Changing the thresholds of the Schmidt trigger allows you to change the range of set temperatures.

However, as mentioned earlier, this device is unreliable and has functional drawbacks - the possibility of overshooting, especially with a control system having hysteresis and delay, as well as the possibility of a catastrophic failure in case of failure of the controller itself, or with a short circuit in the heater.

The objective of the proposal is to increase the reliability of the device to stabilize the temperature of the product by eliminating the likelihood of overheating or catastrophic failure during any one failure in the device or in the heater and expanding the functionality of the device due to redundancy, ensuring the possibility of combining the role of the temperature controller and heater in one monoblock and increasing speed .

This problem is solved in that in a device for stabilizing the temperature of the product, containing the device’s power supply circuit, a temperature sensor connected in series, an amplifier connected to the second power supply circuit, and a transistor, the output of which together with the first power supply circuit forms the device output for connecting the heater, are introduced in series connected by a second temperature sensor, a second amplifier connected to a third power circuit, and a current generator, while the output of the current generator is connected in series with said trans Storey and connected to the common power circuit device.

In addition, the second and third power circuits are made in the form of stabilized power sources.

In addition, the first and second temperature sensors, a transistor, and a current generator are made with a minimum transitional thermal resistance in the form of a monoblock on a heat-conducting surface designed for heat exchange with the body of the product on which the device is installed.

The drawing shows a block diagram of a device for stabilizing the temperature of a product, each block of which is illustrated for example by an electrical circuit diagram, while the following notation is used in the drawing and in the text:

1 - temperature sensor,

2 - amplifier

3 - second temperature sensor,

4 - second amplifier

5 - current generator,

6 - the second power circuit,

7 - the third power circuit,

N1 - the first power circuit,

N2 - common power circuit,

N3 - device output,

N4 - device output,

R _H is a heater

VT3 - transistor,

E is the voltage of the device

GND is a common power circuit.

Made nodes of the device as follows.

Temperature sensor 1 is formed by a voltage divider from RT1 and resistor R2. Its output voltage depends on the voltage of the second power circuit 6 supplied to it, and on the ratio of the resistances RT1 / (RT1 + R2), and, therefore, on the temperature of the thermistor RT1. The amplifier 2 on transistors VT1 and VT2, made according to the Schmidt trigger scheme, is actually a temperature setter and at the same time an amplifier. Its mode sets the response and release thresholds for voltage, determined in a first approximation by the ratios of the resistances of the resistors R3 / R4 and R3 / R7 and the supply voltage supplied to this amplifier from the output of the second power circuit, in fact - from the voltage regulator 6. In this case, the trigger thresholds Schmidt and the output voltage of the temperature sensor 1 at given temperatures must correspond to each other. The transistor VT3 opens by a signal from the output of amplifier 2 (when the Schmidt trigger is triggered) by the voltage from resistor R7.

The second temperature sensor 3 is formed by a voltage divider from the resistor R10 and the RT2 thermistor connected to the third power supply circuit 7. The output voltage of this temperature sensor depends on the voltage on this power supply circuit 7 and the resistance ratio R10 / (RT2 + R10) and, therefore, on temperature RT2 thermistor. The second amplifier 4 on the transistor VT4 and resistors R11-R13, also connected to the third power circuit, in fact - to the voltage regulator 7, operates in non-linear mode: depending on the ratio of the voltages on the emitter and the base of this transistor, it can be completely closed (with real the product’s temperature is higher than the maximum allowable), operate in linear mode (the product temperature must be within the specified limits) or switch to saturation mode (at a real product temperature below the minimum allowable). At the same time, on the linear section of the output characteristic of the second amplifier 4, its output voltage across the resistor R13 changes from zero to the maximum value determined by the current of the transistor VT4 and the resistance of the resistor R13. The beginning and end of the operation of the transistor VT4 of the second amplifier 4 in linear mode and the voltage of the second temperature sensor 3 at given temperatures must also correspond to each other.

The device as a whole maintains the temperature of the product within

t _min <t <t _max

where t is the current value of the temperature of the product,

t _min - the minimum allowable temperature value of the product,

t _max - the maximum allowable temperature value of the product.

It should be noted that any well-designed and manufactured device in the system will not be able to realize its positive qualities, if you do not take into account the invisible "little things." The application of the proposed device requires that good thermal contact of the temperature sensor and heater with the body of the product be ensured. To ensure this, the first and second temperature sensors should be structurally configured to minimize the transient thermal resistance between them and the body of the product on which the device is installed. To do this, they are part of the proposed device placed on a heat-conducting surface (for example, on a material having high thermal conductivity), which is tightly adjacent to the surface of the product. This reduces latency and ensures accuracy when measuring the temperature of the product body. Transistor VT3 is also located on a heat-conducting surface. The need for this is discussed below.

The device as a whole receives the supply voltage E through the first circuit N1 relative to the common circuit N2 (GND). At the same time, to ensure the reliability of the device and ensure the specified temperature in the product, it is advisable to use two independent secondary power sources 6 and 7 as the second and third power circuits, in the simplest case made in the form of parametric voltage stabilizers on resistors R1 and R2 and zener diodes VD1 and VD2, and connected to the first power circuit N1 with voltage E, as shown in the drawing. It is necessary to carry out the power circuits separately because in the event of a failure that causes a sudden increase in the voltage of a single power source (for example, according to the type of open in the zener diode circuit), the output current of the device can increase significantly due to an increase in the control voltages at the inputs of transistors VT3 and VT5, there is a possibility of overheating of the product or failure of the heater. With high reliability of a hypothetical secondary power source, the power circuits can be combined without losing the reliability of the device for this reason. But the high reliability of one power source is much more difficult to provide than to provide two simple voltage regulators in the device. In addition, the use of two power circuits with different voltages makes it easier to provide optimal output voltages of amplifiers 2 and 4 for controlling transistors VT3 and VT5.

Each of the nodes 1-7 of the device can be performed differently from that shown in the drawing. Their execution depends on the required range and the required accuracy of maintaining the temperature, preferred for the application of the elemental base, the developer's addiction to certain technical solutions, etc. Each amplifier 2 and 4 can be performed either with a linear pass-through characteristic in the temperature stabilization range (as the second amplifier 4), or with hysteresis (as the first amplifier 2), on transistors or on operational amplifiers. The essence of the proposal from the point of view of its function and the reliability of the device does not change. In this case, in the first case, the temperature stabilizer will operate in a linear mode, ensuring smooth maintenance (stabilization) of the temperature within a given temperature range, in the second case it will act as a two-position controller, including a heater at a given lower temperature and turning it off after heating to a predetermined temperature upper temperature value.

Consideration of the operation of the device can be started with a hypothetical situation when the product overheated, with t> t _max , and amplifiers 2 and 4, by signals from their temperature sensors, completely removed the control voltages from the power elements VT3 and VT5.

At elevated temperatures, the resistance of RT1 and RT2 thermistors have minimal values. At the same time, by reducing the resistance of thermistor RT1, the potential based on transistor VT1 leads to its opening, transistor VT2 closes, the voltage across resistor R7 drops to zero, and transistor VT3 also closes. By reducing the resistance of the thermistor RT2, the voltage between the base and emitter of the transistor decreases and the transistor VT4 also closes, while the voltage at its output on the resistor R13 drops to zero and the transistor VT5 of the current generator 5 also closes. With the closed transistors VT3 and VT5, the current does not flow through the heater R _n and the product heated by it starts to cool.

In order for the product heating process to start again, it is necessary to ensure the inclusion of both transistors VT3 and VT5. Moreover, the sequence of their inclusion is indifferent. Changing the state of the nodes of the device when shown in the drawing is as follows. As the product and the RT1 and RT2 thermistors cool down, their resistance increases. In accordance with a change in the resistance of RT1 and RT2 thermistors, temperature sensors 1 and 3 change their output voltages. There comes a time when the transistor VT4 of the second amplifier 4 starts to open, a voltage appears on the resistor R13, which is supplied to the control input of the transistor VT5 of the current generator 5. However, the current through this transistor does not flow, despite the increase in the control signal on its control electrode as the product cools down because the transistor VT3 is still closed.

As the product and the RT1 thermistor cool down, its resistance also increases. In accordance with the change in the resistance of the thermistor, the voltage at the output of the temperature sensor 1 changes and there comes a time when the transistor VT1 of the first amplifier 2 closes, and the transistor VT2 opens and jumps in voltage from the resistor R7 to the control electrode of the transistor VT3 and this transistor also opens. From this moment, current begins to flow through the heater R _n , since the transistor VT5 of the current generator 5 has already been opened earlier (at a higher temperature of the product). The voltage from the output of the second amplifier 4 at the control input of the transistor VT5 at this moment at the minimum temperature has a maximum value, and the current of the current generator 5 at the transistor VT5 and the total power transmitted to the product heater will also have a maximum value of I _max and E · I _max . From this moment, the heating of the product begins. If in this case the theoretically possible heater current I _n = E / R _{n is} less than the maximum possible current I _{max of} the current generator, then most of the supply voltage E will be applied to the heater R _n .

As the product heats up, the resistance of RT2 decreases, the output signal from the second temperature sensor 3 changes, the output signal from the output of the second amplifier 4 decreases to the control input of the transistor VT5 of current generator 5, the output current of current generator 5 decreases and the total power used to heat the product decreases . Together with a decrease in the current through the heater R _n , the voltage drop across it also decreases. In this case, a noticeable voltage drop appears on the transistor VT3, the power allocated to it increases. In order for this power not to overheat the transistor, as well as to heat the product, the transistor VT3 must be installed with a minimum transient thermal resistance between its body and the device body and then between the device body and the product body. Moreover, it is advisable to "utilize" the heat generated by the remaining blocks and elements of the device as a whole, i.e. through the device case transfer to the product case. In this case, not a single element of the device will overheat, since the body of the product in this situation will be used as a heat sink.

Further, as the current through the heater decreases, the total power spent on heating the product decreases. In real conditions, a state occurs when the power dissipated by the product and the power supplied to the heating are equal. There is a thermal equilibrium that can last as long as you like. In this case, the temperature of the product will be stable and be in a predetermined temperature range.

If the heating power of the product is still sufficiently large for the product and, despite the decrease in the total heating power, the temperature of the product increases, then the state will come when amplifier 2 removes the control voltage from its transistor VT3, the current through the heater R _n disappears. With the correct design and adjustment of the device, both temperature sensors together with their amplifiers and independently of each other should provide the process of maintaining the temperature of the product within the specified limits. This is required so that a failure of a short circuit device of one of the transistors VT3 or VT5 does not lead to a change in the thermal regime of the product.

Any failure of any one of the elements of this device can lead to only one type of failure of the device as a whole, namely, only to a failure of the "open" type, i.e. the impossibility of heating the product. Failure of the device of the type "short circuit" in the proposed device for any failure of one element is impossible, and that is why. A hypothetical failure of one element can lead to the inclusion (or breakdown) of one of the transistors VT3 or VT5, while the other transistor, together with its control channel, the temperature sensor - amplifier transistor VT5 (or VT3) will work normally and will maintain the temperature of the product in specified limits. In this case, in the case of a short circuit of the transistor VT5, the role of the current generator will pass to the transistor VT3, since the resistance R15 and the residual resistance of the closed (open) transistor VT5 will serve as negative feedback for the transistor VT3. To ensure this mode, the voltage at the control electrode of transistor VT3 is sufficient to have slightly more than at the control electrode of transistor VT5 of the current generator. The implementation of this mode in the proposed device should not cause any difficulties for the developer, since these transistors are controlled from independent power circuits and the voltage on these circuits can be provided based on these requirements.

The proposed device for failure type "break" can be duplicated by a second similar device installed on the product next to the first. At the same time, they can work both simultaneously and alternately. While maintaining the temperature field of extended objects, for example, in technological equipment with a heating jacket, on which a predetermined number of such devices can be installed, a failure of the “break” type heater in one of the heaters can be compensated by neighboring heaters, while overheating even in one location can lead to adverse effects.

The proposed device can operate normally with a partial or full (short) circuit in the heater circuit R _n (this mode of operation of the device is considered normal and is provided for by the circuit and design of the proposed device). To implement this mode, instead of the nominal resistance of the heater, a small resistance or jumper is installed between the output contacts N3 and N4. In this case, the proposed device operates as follows. Under conditions of reduced temperature of the product on which the proposed device is installed in the form of a monoblock, transistors VT3 and VT5 are turned on using signals from two temperature sensors, while transistor VT5 of current generator 5 provides a certain current, for example, maximum I _max at minimum temperature. An open transistor VT3 transmits this current without restriction, but it no longer works in key mode, but in linear mode, in fact - also in current generator mode. In this mode, between its output contacts (drain-source or collector-emitter), the voltage is close to the supply voltage E minus the voltage drop across the current generator (on resistor R15 and transistor VT5). At the same time, a power close to the maximum power supplied by a power source with a voltage E in this mode at a maximum current I _max is released on the transistor VT3. The transistor VT3 starts to warm up and through the design of the device transfer heat to the product on which this device is installed, made in the form of a monoblock. In total, the product transfers power equal to the product E · I _max . The rest of the process of maintaining the temperature of the product is carried out by analogy with the above, including the heating power.

The device is also operable with any high-resistance heater R _n consuming a load current less than the maximum possible for this device, i.e. E / R _n <I _max . In this case, as the product heats up, the resistance of the thermistor RT2 decreases, the output signal from the second temperature sensor 3 changes, the output signal from the output of the second amplifier 4 decreases to the control input of the transistor VT5 of the current generator 5. However, the output current of the current generator 5 decreases and the total power decreases, going to heat the product does not occur. This mode is maintained to that state in terms of product temperature, until the load current equal to E · R _n and the actual current of the current generator 5 are equal, decreasing with increasing temperature from I _max . With further heating of the product, the load current to the heater decreases, as described above.

Thus, the proposed device can operate in two modes: both as a heater switch by signals from temperature sensors, and as a heater directly by signals from the same temperature sensors, maintaining the temperature of the product within specified limits. Moreover, with any failure of one element, this device eliminates overheating of the product on which it is installed. Moreover, the proposed device, made in the form of a monoblock with a short-circuit output, when turned on without thermal contact with anything, will also not overheat, including in case of any one failure in it. This is ensured by the fact that the heater (in this mode, the VT3 transistor) at maximum power on it quickly heats up and heats the monoblock. Temperature sensors installed in the same monoblock will quickly reduce the heating power or turn off the heating completely. In fact, the device, made in the form of a monoblock, works in this case in the normal mode with a very small connected mass, requiring heating.

The proposed device should be placed on a heated product with a minimum thermal resistance. For this, the device is made in the form of a monoblock with a good heat-conducting surface, providing heat exchange between the product body and this heat-conducting surface. The placement of the temperature sensor and transistor VT3, which acts as a heater in one monoblock case, is designed to provide a minimum delay in the temperature measurement circuit "product body - temperature sensor" and in the executive circuit "heater (transistor case VT3) - product body". When using an external heater R _{n, the} distance between it and the monoblock of this device should also be as small as possible to reduce the delay in the temperature measurement circuit "product body - temperature sensor".

In conclusion, it should be noted that the proposed set of features in the device proposed by the author has not been met before to solve the problem and does not follow explicitly from the prior art, which allows us to conclude that the technical solution meets the criteria of "novelty" and "inventive step".

Standard elements can be used as elements for the implementation of the device, including thermistors (either resistors, resistance thermometers, thermocouples), transistors (or microcircuits with adjustable parameters within specified limits), and powerful transistors as power controlled elements, in including those made according to Darlington’s scheme, capable of not only passing the heater current through itself, but also transmitting through its housing the power necessary to heat a particular product in a particular place (most perspective for the implementation of these functions - powerful field effect transistors). As a design of the device for accommodating temperature sensors and power transistors in it, it is advisable to use a small-sized monoblock with a heat-conducting surface, which provides heat exchange with the body of the product.

At the enterprise, the device is at the stage of development of technical specifications.

References

1. RF patent No. 2090014, Н05В 1/02.

2. RF patent No. 2160920, G05D 23/19.

Claims (3)

1. A device for stabilizing the temperature of an article containing interconnected power circuits, a temperature sensor connected in series, an amplifier connected to a second power circuit, and a transistor whose output, together with the first power circuit, forms the output of a device for connecting a heater, characterized in that a second temperature sensor, a second amplifier connected to a third power circuit, and a current generator whose output is connected in series with the said transistor are introduced in series Ohm and connected to the device’s common power circuit. 2. The device for stabilizing the temperature of the product according to claim 1, characterized in that the second and third power circuits are made in the form of stabilized voltage sources. 3. The device for stabilizing the temperature of the product according to claim 1, characterized in that the first and second temperature sensors, a transistor and a current generator are made with a minimum transient thermal resistance in the form of a monoblock on a heat-conducting surface, designed for heat exchange with the body of the product on which the device for stabilization of the temperature of the product is set.