SU754373A1 - Device for regulating temperature in resistance furnaces - Google Patents

Description

The invention relates to an automatic temperature control in resistance furnaces, in which NEs with varying resistance are mainly used as heating elements (NEs).

A device for temperature control is known, which includes a magnetic amplifier, an electronic potentiometer, equipped with a rheostatic setting device and a positioner, through the contacts of which one of the control windings of the magnetic amplifier is connected to a two-stage setting device.

The scheme provides independent separate control of the heating power and dynamic properties of the system, and also regulates the temperature in resistance furnaces [1].

However, it does not provide for control over the current of the heating element of the furnace, the absence of which does not allow to take into account the change in their resistance during operation, i.e. aging.

The closest technical solution is a two-stage temperature control system for an electric co2 furnace.

resistance, which consists of a temperature sensor, an automatic potentiometer, a control unit, a contactor actuation device and an adjustable voltage source in the form of a transformer ₅ pa with taps.

The control unit contacts via an intermediate relay control the contactor actuation device. Such positioning systems manage a group of heating elements connected in parallel [2].

The disadvantages of positioning systems is that they do not maintain the constancy of the regulated power of each heating element, which increase their resistance during operation.

In practice, the resistance of silicon heaters increases by 3-4 times compared with the original. Since NEs in one group age unevenly, this causes an overload of individual NEs with less resistance, which reduces their service life, and also leads to an uneven distribution of power between

3

754373

four

NE in the group and, as a consequence, to the uneven distribution of temperature in the furnace.

The aim of the invention is to improve the accuracy and reliability of the device.

This goal is achieved by the fact that the device contains, by the number of heaters, control units consisting of a series-connected rectifier, reference element, integrator, null indicator, amplifier, pulse shaper, trigger and element AND, reference pulse generator, element OR, voltage level selection blocks according to the number of heaters, containing chains from a series-connected element I, a rectifying diode and a driving resistor, the second terminals of which are interconnected, current sensors by the number of heating The regulated voltage source consists of a series-connected converter code - voltage, comparator, counter and decoder, the outputs of which are connected to the first inputs of the corresponding elements AND blocks of voltage level selection, the second inputs of which are connected to the output of the amplifier of the corresponding control unit, and the outputs of the current sensors connected to the first inputs of the corresponding rectifiers, the second inputs of which are connected to the output of the reference pulse generator associated with the second inputs of the elements And control units, the third inputs of which are combined with the inputs of the corresponding pulse shapers, the outputs of which are connected to the second inputs of the flip-flops of subsequent control units and the corresponding converter inputs code - voltage, another input connected to the output of the OR element, inputs connected to the outputs of the control elements And , the inputs of the comparison elements of which are connected to the output of the automatic potentiometer, and the control inputs of the actuating elements are connected with the common output of the master register lines of the respective voltage level selection blocks.

The proposed scheme makes it possible to evenly distribute the power between the heating elements by regulating the activation time of each heating element separately and automatically switching the supply voltage level of the actuator of the heating element (NE) taking into account its individual aging, that is, changes in resistance during operation.

The magnitude of the task, which determines the required power delivered to the furnace, is the same for all NEs.

In the process of aging, the NE, i.e., when its resistance increases, to maintain power at a given level, the ON time automatically increases until the time when the ON time _{включения ΒΚΑ} becomes equal to the cycle time Tc (see Fig. 2).

Then there is an automatic switch to a new higher level of supply voltage of all non-electric cells at the same time, which also maintains a uniform power distribution between individual non-electric cells. The process is limited to the inclusion of the last step voltage. Thus, the required power is maintained at each NE with a wide change in its resistance.

Uniform distribution of power between the ne and the maintenance of it within acceptable limits allows to increase the service life of ne, because ne do not prove to be overloaded in the process of work.

The uniform distribution of power between the non-electrolytes in turn leads to an even distribution of the temperature in the furnace, which improves the quality of the products processed in the furnace.

FIG. 1 is a schematic diagram of the proposed device; in fig. 2 is a diagram of the cycle of operation of the NES.

The device consists of the control unit 1 of each heater 2. Each control unit 1 includes a rectifier 3, a comparison element 4, the output of an automatic potentiometer 5, an integrator 6, a null indicator 7, an amplifier 8, an element 9 And, connected to one of the inputs shaper 10 pulses and trigger 11.

The output of the pulse shaper 10 is connected to one of the trigger inputs of this control unit 1 and the trigger 11 of the next control unit 1. The device also contains a sensor 12 temperature thermocouple.

The inputs of the element 9 And connected to the output of the generator 13 reference pulses, which is common to all blocks 1 of the control unit output zero indicator 7. To one of the inputs of the rectifier 3 is connected to the generator output 13 of the reference pulses, and to another sensor 14 current corresponding heating element 2 .

The outputs of each element 9 And connected to the element 15 OR, the output of which is connected to the source 16 of an adjustable voltage.

The adjustable voltage source 16 contains a code converter 17 - a voltage to which the drivers of 10 pulses are connected, in turn, connected to the output of a zero-indicator ^t. Aor 7 of each control unit 1, a comparator; p 18, a counter 19 with a generator 20 connected to it single pulses, the decoder 21, the outputs of which are connected to blocks 22 of the voltage level selection of the actuating element 23 for each ne 2. The generator of single pulses is also connected to the inputs of the flip-flops 11 of all regulators of the group.

Each unit 22 of the voltage level selection consists of parallel connected

754373

five

chains consisting of series-connected elements 24 And, a rectifier diode 25 and a setting resistor 26. One of the inputs of the element 24 And connected to the output of the amplifier 8, the corresponding control unit 1, and the other input to the corresponding output of the decoder 21. To the outputs of the blocks 22 select the voltage level connected actuators 23.

The device works as follows.

When you turn on the power from a single pulse generator 20 single pulse counter 19 levels, the Converter 17 code - voltage and triggers 11 are set to their original state. In this case, the trigger And the first control unit prepares the circuit element 9 to work, and the remaining triggers 11 lock the corresponding elements 9 I.

This sets a certain initial level of supply voltage of the heating elements. This level corresponds to a certain state of the counter 19 and the presence of a signal at one of the outputs of the decoder 21, which is fed to the input element 24 And block 22 of the choice of the voltage level.

When the temperature in the furnace deviates from the setpoint, the automatic potentiometer 5 generates a mismatch signal proportional to this deviation. This signal is fed to one of the inputs of the element 4 comparison. The other input receives the rectified signal from the sensor 14 of the current of the heating element 2.

The difference signal is fed to the input of the integrator 6, which, depending on the sign of the signal, enables or disables the null indicator 7. The time the null indicator 7 is in one of these states depends on the change in the value of the difference signal at the input of the integrator 6.

When triggered null indicator 7 through the amplifier 8, a signal is issued to the element 24 And, which closes the actuating element 23 and turns off the heating element 2.

The integrator 6 and the zero-indicator 7 form the work cycle of the NE 2. The work cycle consists of the ON time of the ON 2 4 _ON and the pause time pluses (Fig. 2).

The input of the circuit element 9 NE 2 signal from the generator 13 reference pulses and the signal from the output of the null indicator 7 of the corresponding NE.

When these two signals coincide in time, the output of element 9 will be the number of impulses of the generator 13 reference pulses, proportional to the ON time 2. The driver 10 pulses when the null indicator 7 closes and the trigger 11 switches to a state where its output blocks the element 9 AND By this

6

the same signal from the driver 10 pulses of the Converter 17 code-voltage is set to its original state, and the trigger 11 of the next control unit 1 is transferred to the position in which its element 9 And is prepared for work. Outputs of all elements 9 And served on the element 15 OR. which is connected to the converter 17 code-voltage. From the output of the inverter 17, the voltage proportional to the number of pulses at the input goes to the comparator 18.

The comparator 18 compares the voltage at the output of the code-to-voltage converter 17 and the reference voltage of the Weng. The value of ν _οπ g is selected from the condition of the maximum voltage value at the output of the code-voltage converter 17 and its opposite sign. The maximum value at the output of the converter 17 of the cat is the voltage is reached prc this cycle of operation of the ne 2 when its turn-on time 1 on becomes equal to the cycle time Tc (see Fig. 2).

When the voltage at the input of the comparator 18 becomes equal to Vo _p r he works, it changes its state and counter 19 through the decoder 21 to connect the chain unit 22 following the selection voltage level which establishes a higher level supply voltage actuator 23 NE 2. The values defining the resistances of resistors 26 In block 22, the selection of the voltage level is selected depending on the magnitude of the voltage level of the NE2. Thus, the switching of the supply voltage level of the actuating element 23 of the heating circuits takes place. elements. If the comparator 18 does not work, then the entire process of working with an estimate of the on / auxiliary time of the voltage converter 17 is repeated, but now the duration of the on-time on the second controller of the group, then the third, and so on is checked. After checking the duration of the last controller in the group, the time ίβ ^ of the first regulator is checked again. The process continues until the need to move to the next voltage level is detected.

Claims (1)

Claim An apparatus for controlling the temperature in a resistance furnace, comprising a control unit connected in series a temperature sensor and automatic potentiometer source of regulated voltage and a chain of series-connected actuators and voltage circuits of series connected actuators and the heaters, characterized in that, for the purpose ^- 7 improve the accuracy and reliability of the device; it contains, by the number of heaters, control units consisting of a series-connected rectifier, reference element, integrator, null indicator, amplifier, pulse shaper, trigger and element AND, reference pulse generator, element OR, voltage level selection unit according to the number of heaters, containing chains from a series-connected element I, a rectifying diode and a setting resistor, the second terminals of which are interconnected, current sensors by the number of heating a voltage source consists of a code-voltage converter connected in series, a comparator, a counter and a decoder, to the outputs of which are connected the first inputs of the corresponding elements AND blocks of the voltage level selection, the second inputs of which are connected to the output of the amplifier of the corresponding control unit outputs current sensors ₂₀ svyaza- us to first inputs of respective rectifiers, the second inputs of which podklyu754373 eight “To the output of the generator of reference pulses, associated with the second inputs of the elements And control units, the third inputs of which are combined with the inputs of the corresponding pulse formers, the outputs of which are connected to the second inputs of the trigger of the subsequent control units and the corresponding inputs of the code-voltage converters, another input connected to the output of the OR gate, the inputs connected to the outputs of elements ₁₀ comrade and a control unit comparing element whose inputs are connected to the output of the automatic potentiometer And control inputs of the actuators are connected with a common terminal of resistors defining the respective voltage level selection unit.