SU1265520A1 - Device for automatic air sampling - Google Patents

Abstract

The invention relates to a device for the automatic sampling of an air sample, can be used in the chemical industry and makes it possible to improve the accuracy of the selection of an air sample. The device contains a series-connected filter drive I, a flow booster 2 with a valve 3, and a flow sensor 4. The flow rate booster 2 is connected to a pulse-width modulation voltage generator 14, an adder 13, a first comparison element 12, and an integrator 10. The latter is connected to a volume measurement unit 5, made in the form of an interconnected frequency divider 6 and a counter 7 and connected to the second element 8, compared with a pre-set 9. 9. Cp. f-ly, 2 ill. (L

Description

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The invention relates to the preparation and sampling of air samples and can be used in automated systems to control the cleaning and control of environmental pollution by aerosols, bacteria, dust and gases.

The aim of the invention is to improve the accuracy of sampling the air sample when the hydraulic resistance of the storage filter is changed.

FIG. 1 is a block diagram of a device for automatically taking an air sample; in fig. 2 is a block diagram of a pulse width modulation voltage driver (option).

The device for automatic sampling of the air sample contains a filter drive 1, a flow booster 2 with a power supply valve 23B allowing to adjust the capacity, and a flow sensor 4, a volume measuring unit 5 connected to the output of the flow sensor 4 and consisting of series-connected dividers 6, the counter 7 and the comparison element 8, to which another input is connected to a volume setting device 9, a current flow measurement unit including an integrator 10, a flow setting indicator 11 and a comparison element 12. The outputs of the elements 8 and 12 of the comparison and the flow master 1 are connected to an adder 13, the output of which is a pulse width modulation voltage regulator 14.

A pulse width modulation voltage driver 14 consists of a series-connected electronic key 15, a linearly varying voltage integrator 16, an amplitude comparator 17 and a comparison unit 18, and a square pulse generator 19, the output of which is connected to the control input of the electronic key 15 and the first input of the comparison unit 18.

Filter drive 1 can be made in the form of an electrostatic filter or a Petri dish with a nutrient medium, or a liquid filter absorber, etc.

The flow rate booster 2 with a valve 3 in the power supply circuit is a membrane type air blower with an engine, in the power supply circuit of which a valve 3 is installed in the form of an electronic switch.

The tachometer-type flow sensor 4 consists of an impeller placed in an air flow whose rotational speed is proportional to the flow rate of the medium being analyzed, and a speed and rotation recorder of the impeller in the form of an LED-photodiode optical coupler.

The volume measurement unit 5 is made of a serially connected frequency divider 6 with a variable division factor and a pulse counter 7. The pulse sequence from the output of sensor 4

the flow rate is converted by a frequency divider 6 into a sequence of pulses, each of which corresponds to a unit of measure for volume (e.g., a liter). A pulse counter 7 registers the number of pulses arriving at its input and outputs at its output a value proportional to the measured sample volume.

The unit 9 for the volume of the air sample is an electromechanical converter for the PNR-UC codes, at the output of which the value of the required volume is given in the binary code.

The generator 19 rectangular pulses, made according to the scheme of self-oscillatory

multivibrator, sets the pulse frequency of the engine power prompted air flow 2. The frequency determines the frequency of the sawtooth voltage at the output of the integrator 16 of a linearly varying voltage, made on the basis of an integrator with a reset. The integrator is reset with the electronic key 15. The ramp of the sawtooth voltage is determined by the magnitude of the reference voltage (Jo. The integrator output voltage 16

arrives at the first input of the amplitude comparator 17, to the second input of which voltage is supplied from the output of the adder 13. Latitude-modulated voltage is formed at the output of the comparison unit 18, to the first input of which impulse

the voltage from the generator output is 19 rectangular pulses, and to the second input is from the output of the amplitude comparator 17. The flow setting device 11 is based on the PPM-10 electromechanical code converter, from the output of which the voltage in analog form is fed to the inputs of the comparison element 12 and adder 13. Adder 13 can be implemented on the basis of operational amplifiers.

The device works as follows.

The analyzed air is sucked by the flow booster 2 through the electrostatic filter 1 and causes the turbine of the tachometer flow sensor 4 to rotate. The rotational speed of the sensor impeller is converted by the photoelectric method using an opto-optic pair of LED light emitting diodes to the frequency of rectangular impulses. owls entering the input of block 5 and measuring the volume and the input of the integrator 10, on

The Q output of which produces a constant voltage proportional to the current consumption of the sample being analyzed.

In unit 5 for measuring volume, a sequence of rectangular pulses is fed to the input of a frequency divider 6,

5 the output of which produces a pulse whose frequency is proportional to the volume expressed in liters of the sampled air sample.

Counter 7 registers the number of pulses arriving at its input, and outputs at its output a value in binary code proportional to the current sample volume. This value is fed to the first input of the first comparison element 8, to the second input of which the specified value of the volume of the sample taken with the unit 9 of the volume is supplied to the binary code. The coincidence of the current and predetermined volumes of the sampled sample leads to the formation of a pulse at the output of the first comparison element 8, which enters the input of the adder 13, from which the signal through the pulse-width modulation voltage regulator 14 is applied to the control input of the valve 3, which interrupts the power circuit engine flow rate 2, and sampling is stopped.

The proposed device for automatic sampling of air samples ensures the stabilization of a given flow rate. For this purpose, rectangular pulses from the output of the flow sensor 4 are fed to the input of the integrator 10. From the output of the integrat 10, a voltage proportional to 11i., 1: the flow to it goes to one of the Bxojoi second comparison element 12, to the other input of which is fed constant voltage from flow control unit 11.

The error voltage, proportional to the difference between the set and the actual flow, from the output of the comparison element 12 is fed to the input of the adder 13, to the other input of which the voltage is supplied from the output of the flow setting unit 11.

The voltage from the output of the adder 13 is fed to the input of the amplitude comparator 17. In the block of the shaper modulation voltage regulator 14 to the second input of the amplitude comparator, the voltage of the linearly varying voltage is supplied from the output of the integrator 16. The integrator 16 generates a sequence of pulses of linearly varying voltage with a frequency determined by the generator 19 of rectangular pulses, which controls the operation of the electronic key 15. The electronic key 15 periodically razrn / kete integrating capacity in the integrator of linearly varying voltage. At the output of the amplitude comparator 17, rectangular pulses are formed, the duration of which is determined by the ratio of the voltages at the inputs of the amplitude comparator 17 These pulses arrive at the first input of the comparator unit 18, to the second input of which pulses are delivered from the generator 19 rectangular pulses

same frequency but different duration. At the output of the comparator unit 18, a voltage is generated by the pulse-width modulation, the duty cycle of which is determined by the voltage supplied from the output of the adder 13. With the output of the former 14, the voltage is supplied to the control input of the valve 3 connected to the power source of the engine booster 2 flow rate, and changes the frequency of rotation of the engine, and hence the flow of air inversely proportional to the duty cycle of the control pulses, corresponding to the change in the hydraulic resistance of the storage filter.

The invention provides automatic selection of the required volume of the air sample with a given stabilized flow rate in a wide range when the flow resistance of the filter is changed during operation.

Claims (2)

1. A device for automatic sampling of air samples, containing a sample filter storage device installed in the air supply line, a flow rate booster with a capacity control in the power supply circuit, a flow sensor connected to the sample volume measuring unit with a volume setting device and a comparison card and a current flow measurement unit, the control input of which is connected to the flow sensor, characterized by a TL. .to, in order to improve the accuracy of sampling the air sample when changing the hydraulic resistance of the storage filter, the device is equipped with an adder and a pulse width modulation voltage driver connected by an output to the flow rate control regulator, the first input of the adder being connected to the output of the comparison unit for measuring the sample volume, the second and third inputs of the adder are connected to the corresponding outputs of the current flow measurement unit, and the output of the adder is connected to the control input pulse width modulation voltage driver. 2. The device according to claim 1, characterized in that the current flow measurement unit is made in the form of an integrator and a flow rate adjuster connected to the reference element connected to the second inlet of the adder, and the output of the adjuster is connected to the third adder input. B) i.o / n.f3 1 GI