RU2284378C1 - Self-contained measuring unit for automatic control system of aluminum electrolysis process - Google Patents

Abstract

FIELD: measurement, monitoring and automation units for aluminum electrolysis process.

SUBSTANCE: provision is made for galvanic isolation of remote measuring unit from AC 220-V mains since unit is supplied directly from electrolyzer and may be located on busbar supplying current to electrolyzer. Radio channel used for galvanic isolation excludes lines of communication of electrolyzer with automatic control system of technological process, thus enhancing reliability of information facilities and safety of electrolysis block attending personnel.

EFFECT: reduction of error due to action of magnetic fields; extended dynamic range of input signals; reduced number of communication lines; enhanced operational reliability of unit as a whole.

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Description

The invention relates to the field of measuring, control and automation, in particular to linear amplifiers and DC voltage converters with a variable component up to 30 Hz with galvanic isolation and coordination with the inputs of the automatic process control system of aluminum electrolysis.

A device is known for monitoring the technological state of an aluminum electrolysis cell (USSR Author's Certificate No. 889748, published in BI No. 46 of 12/15/81) containing: a series current oscillation measuring system consisting of a series-connected voltage converter with galvanic isolation and an active filter; and the circuit for measuring the variable component of the voltage of the electrolyzer is an active filter connected to the output of the switch; sequentially connected by an adder, an amplitude detector and an analyzer, while the inputs of the adder are connected to the outputs of the active filters, the output of the analyzer is connected to a series-connected analog-to-digital ohmmeter and output device for printing, a setter of the average value of the ohmic resistance connected to the active filter of the current branch, a setter of duration measurement connected to the input of the switch, a current limiter connected to the adder, a comparison device connected at the input to the device Displayed on the printing group of parallel-connected input and output connected to the switch control keys, which yields to the active filter and the analyzer.

The disadvantage of this device is the low accuracy of information transfer from the electrolyzer to the decision-making system (to the ACS of electrolysis). Significant additional errors are associated with the adjusters of the average value of the ohmic resistance and the duration of the measurement of analog signals. In addition, an additional 220 V power supply is required.

The well-known M-DM amplifier with galvanic isolation (USSR Author's Certificate, No. 1358066, published in BI No. 45 dated 07.12.87, prototype), comprising an input low-pass filter, a voltage-frequency converter, a galvanic isolation element, a frequency-pulse converter , a pulse-width demodulator, a voltage-current converter, in which the output of the input low-pass filter is connected to the input of the galvanic isolation element, through a voltage divider and a voltage-frequency converter, and between the output of the element Galvanic separation and the input PWM frequency converter of the demodulator is entered - the pulse duration.

The disadvantage of the prototype is the significant dependence of the accuracy of the signal conversion on the electromagnetic field due to several stages of signal conversion, the need for a power source from the 220 V network, which reduces the reliability of the device and increases the complexity of its operation.

The objective of the proposed technical solution is to increase the reliability, transmission capacity of the signal from the object to the input of the control system, reduce the measurement error, expand the dynamic range of the input signals and provide power to the device nodes from the source of information signals - the electrolyzer.

To solve this problem, in an autonomous measuring unit for automatic process control systems of aluminum electrolysis containing a comparator, voltage divider, active low-pass filter, galvanic isolation element, according to the invention, additionally included: low-frequency amplifier, limiter, converter, analog-to-digital converter (ADC) , Voltage regulator; the inputs of the limiter, active low-pass filter, voltage divider and the signal input of the comparator are combined and are the input of the measuring unit, and the output of the limiter is connected through the converter to the input of the voltage regulator, the first output of which is connected to the power inputs of the voltage divider, active low-pass filter , low-frequency amplifier, ADC, galvanic isolation element and comparator, the second output of the voltage stabilizer is connected to the reference input of the comparator, in addition, the output of the comparator with it is single with the control input of the voltage divider and the first input of the ADC, and the output of the voltage divider is connected to the second input of the ADC, and the output of the active low-pass filter is connected through the low-frequency amplifier to the third input of the ADC, the output of which is connected through the galvanic isolation element to the input of the ACS of aluminum electrolysis .

A significant difference of the device lies in the fact that the inputs of the limiter, active low-pass filter, voltage divider and the signal input of the comparator are combined and are the input of the measuring unit from the source of the information signal - electrolyzer; and the output of the limiter is connected to the input of the converter, the output of the converter is connected to the input of the voltage regulator, the first output of the voltage regulator is connected to the inputs of the voltage divider, active low-pass filter, low-frequency amplifier, ADC, galvanic isolation element and comparator, the second voltage stabilizer output is connected to the reference input of the comparator. Such switching on of the units provides power to all nodes of the device with a stable current, ensuring the operability of the device as a whole when the input information signal changes - the cell voltage in the range from 2 to 80 V.

The second significant difference is that the output of the comparator is connected to the control input of the voltage divider and the first input of the ADC, and the output of the voltage divider is connected to the second input of the ADC, in addition, the output of the active low-pass filter is connected through the low-frequency amplifier to the third input of the ADC, and the ADC output is connected to the input of the galvanic isolation element. Such a circuit solution provides high accuracy of the transmission of information signals: the operating voltage of the electrolyzer, including anode effects, and a variable component - technological noise of the electrolyzer in the range of 0-20 Hz, carrying useful information about the operating mode of the electrolysis bath.

The drawing shows a functional electrical diagram of the device, where the following notation is introduced: the source of the information signal is an electrolyzer 1, a limiter 2, an active low-pass filter 3, a voltage divider 4, a comparator 5, a converter 6, a voltage regulator 7, a low-frequency amplifier 8, analog digital converter (ADC) 9, galvanic isolation element 10, industrial control system 11.

Autonomous measuring unit for ACS TP aluminum electrolysis works as follows. The information signal from the output of the electrolyzer 1 is supplied simultaneously to the inputs of the limiter 2, the active low-pass filter 3, the voltage divider 4 and the signal input of the comparator 5. The limiter 2 is made on transistors and a zener diode, it limits the voltage to 5.1 V, which ensures a stable mode the operation of the converter and the power source as a whole, when the operating voltage of the electrolyzer varies from 2 to 80 V. From the output of the limiter 2, a voltage of 5.1 V is supplied to the input of the converter 6, which converts the input voltage voltage ± 15 V. This voltage is supplied to the input of a voltage stabilizer 7, which is made on integrated circuits and provides a stable voltage of ± 12 V at the first output, which is used to power all active elements of the measuring unit. A stable voltage of +10 V is removed from the second output of the voltage stabilizer and fed to the reference input of the comparator 5, which ensures high stability of the voltage divider 4.

From the output of the comparator 5, the voltage "0" or "1" is supplied to the first input of the ADC 9. The voltage "0" corresponds to the division mode 1: 1, i.e. the mode without the anode effect, and “1” - the 1:10 division mode with the anode effect.

From the output of the voltage divider 4, controlled by the comparator 5, the operating voltage of the electrolyzer is supplied to the second input of the ADC 9.

From the output of the active low-pass filter 3, a signal with a cut-off frequency of 20 Hz and suppression of the industrial frequency of 50 Hz by -40 dB is fed to the input of the low-frequency amplifier 8, where it is amplified and fed to the third input of the ADC 9.

From the output of the ADC 9, the signal in a serial digital code is fed to the galvanic isolation element 10, the output of which is transmitted via twisted pair or over the air to the input of the control system 11 or any other information collection and processing system.

In the proposed device, the problem of galvanic isolation of the remote measuring unit from the AC 220 V is solved, since the device is powered directly from the electrolyzer and can be located on the bus that supplies current to the electrolyzer. The use of a radio channel as an element of galvanic isolation eliminates the communication lines of the electrolyzer with the automatic process control system, which increases not only the reliability of information tools, but also the safety of the operating personnel of the electrolysis building. In the proposed technical solution, the error from the influence of magnetic fields is reduced, the dynamic range of the input signals is expanded, the number of communication lines is reduced, the reliability of the entire device is increased.

Claims (1)

Autonomous measuring unit for automatic process control system of aluminum electrolysis containing a comparator, voltage divider, active low-pass filter, galvanic isolation element, characterized in that it is equipped with a low-frequency amplifier, limiter, converter, analog-to-digital converter (ADC), voltage stabilizer, with The inputs of the limiter, active low-pass filter, voltage divider and the signal input of the comparator are combined and are the input of the measuring unit, and the output of the limiter is connected via an converter to voltage regulator, the first output of which is connected to the inputs of the voltage divider, active low-pass filter, low-frequency amplifier, ADC, galvanic isolation element and comparator, the second voltage stabilizer output is connected to the reference input of the comparator, the output of the comparator is connected to the control input of the voltage divider and the first ADC input, the output of the voltage divider is connected to the second ADC input, the output of the active low-pass filter is connected through the low-frequency amplifier to the third ADC input, Exit is via the galvanic isolation element connected to the input APCS aluminum electrolysis.