SU1621006A1 - Device for digital temperature control - Google Patents

Description

(21) 4463541/24

(22) 07.19.88

(46) 01.15.91. Bul № 2

(71) State All-Union Central Research Institute for Complex Automation

(72) A. B. Chervkov and M. B. Shmuelzon

(53) 621.503.55 (088.8)

(56) USSR Author's Certificate No. 954969, cl. G 05 B 23/19, 1982.

USSR Author's Certificate No. 1372278, cl. G 05 B 19/18, 1988.

(54) DEVICE FOR DIGITAL TEMPERATURE REGULATION

(57) The invention relates to the automation of technological processes. The purpose of the invention is to improve the accuracy of temperature control of an electric furnace. The setpoint temperature is set using the temperature setter. In each r control act, the current temperature is compared with the set one by a signal from the clock generator. If at this time the current temperature is less than the set temperature, the electric heater is turned on, otherwise the heater is not turned on. After turning on the heater, its current is measured and the time of action of the control action (time after which the heater is turned off) is calculated. This time is calculated as the sum of the product of the deviation of the current temperature from the one specified by the proportionality factor and the product of the correction factor by the difference of the reference and measured currents. Thus, the time of action of a correct action depends on the deviation and disturbing effects of indicators such as fluctuations in the supply voltage and aging of the electric heater. 1 silt

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The invention relates to the automation of technological processes and can be used, for example, to digitally control the temperature of electrical resistance furnaces, when a relay element is used as the executive body.

The aim of the invention is to improve the accuracy of temperature control of an electric furnace.

The drawing shows a block diagram of the device.

The device for digital temperature control contains temperature sensor 1, control object 2 (electric furnace), first analog-digital converter 3, 4 pulse generator, comparison unit 5, temperature setpoint 6, first comparison element 7, actuator 8, current sensor 9, second A / D converter 10 and second comparison element 11, subtraction unit 12, standby multivibrator 13, addition unit 14, first multiplication unit 15, proportional factor setting unit 16, correction factor setting unit 17, this unit 18 ground current, second multiply block 19, timer 20.

The device works as follows.

The signal from sensor 1, which characterizes the temperature of the control object 2 (electric furnace), is converted using the first analog-digital converter 3 to a digital code.

With a given discreteness of the signal from the generator of 4 pulses in block 5 comparison is determined by the deviation of e current

O5

ABOUT

temperature values of 7 from the set value T,

U, -T, (1)

The temperature setpoint 7 is set by the temperature setpoint 6.

In the first comparison element 7, the condition under which the activation enable signal is issued through the executive body 8 of the control object 2 is checked. If 7 and T} are equal or if the current temperature is higher than the set one, the electric furnace is not turned on or off if it was in the on state up to this point.

After turning on the heater of the electric furnace 2 by the current sensor 9, a signal is generated that characterizes the current of the electric furnace heater.

The second analog-to-digital converter 10 converts the signal of the sensor 9 into a digital code, which is fed to the input of the second comparison element 11 and to the input of the subtracted subtraction unit 12. In the second comparison element 11, the heater current value is compared to zero. When the condition (where / is the current of the electric heater of the electric furnace) is fulfilled, the output of the element 11 is a signal that is triggered by the waiting multivibrator, which generates an impulse to enable the operation of the addition unit 14. Thus, after turning on the electric furnace, in block 14, the time of the action of the control action tu on the control object 2 is calculated in accordance with the expression

 in + K (/, - /), (2)

where CL is the proportionality coefficient;

Kc - correction factor;

/ - reference value of the current of the electric heater of the electric furnace 2.

The component of the calculated on-time of the electric furnace 2 (tn) Kn-e is calculated in the first multiplication unit 15 and is the component in expression (2), which takes into account the deviation of the controlled parameter.

The value of KP is set by the adjuster 16 of the proportionality coefficient depending on the dynamic characteristics of the electric furnace 2.

The value of L is set by the adjuster 17 of the correction factor when setting up the device and takes into account the structural features of the electric furnace and the heater material

The reference current of the heater / is set by the unit 18 of the reference current for a particular control object 2 and is calculated before its commissioning by the formula

I- &

(3) where R is the resistance of the heater;

UK- rated supply voltage

electric furnaces 2.

The component of the calculated switching on time of the electric furnace Kc (1d- /) is the core

0

five

0

five

0

five

0

five

rectifying component and takes into account the disturbing effects on the electric furnace 2, such as changes in supply voltage and aging of the heater. When the supply voltage decreases, the current of the heater / decreases, the component / ("(/, - /) increases and, therefore, the turn-on time of the heater is adjusted upwards. With an increase in the supply voltage above the nominal value, the turn-on time of the heater decreases.

As the heater ages, its resistance increases due to burnout, the current decreases accordingly, and therefore, due to the correction component, the turn-on time of the heater increases.

The component Cl (13 - /) of expression (2) is calculated in the second multiplication unit 19.

In subtraction unit 12, the difference between the reference and measured currents is determined.

The calculated time 1L is the setting of timer 20, which, after a predetermined time has passed through the actuator 8, switches off the electric furnace 2.

Claims (1)

Invention Formula A device for digital temperature control, comprising a temperature setter, a proportional ratio setter, a subtraction unit, an addition unit, a temperature sensor connected in series, a first analog-to-digital converter and a comparison unit, to the clock input of which a pulse generator is connected and the output of which is connected to the first information input the first multiplication unit and with the input of the first comparison element, the output of which is connected to the input of the enable switch of the actuator, the input coma The shutdown switch is connected to the timer output, characterized in that, in order to increase the temperature control accuracy, the device includes a current sensor, a second analog-to-digital converter, a multivibrator standby, a correction factor setting unit, a reference current setting unit, a second multiplication unit and a second comparison element, the input of which is connected to the output of the second analog-to-digital converter and to the input of the subtracted subtraction unit, the input of which is decremented is connected to the output of the reference current setting device, and the output is connected On the first information input of the second multiplication unit, the second information input of which is connected to the output of the correction factor setting unit, and the output is connected to the first information input of the addition unit, the second information input of which is connected to the output of the first multiplication unit, the output is connected to the timer setup input, and the input resolution is connected to the output of the standby multivibrator, the start input of which is connected to the output of the second reference element, the output of the current sensor is connected to the input of the second analog-digital signal On the converter, the output of the temperature setter is connected to the second input of the comparison unit, and the output of the setting unit of the coefficient of proportionality is connected to the second information input of the first multiplication unit.