RU2473097C2 - Microcontroller metering converter of gas and liquid flow speed - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: microcontroller metering converter of gas or liquid flow speed comprises a microcontroller 1, the first resistor 2, the second resistor 3, a thermistor 4, a capacitance sensor 5, a controlled source of reference voltage 6, the first outputs of two resistors 2 and 3 are connected accordingly to the first and second outputs of the microcontroller, the second outputs of resistors 2 and 3 are connected to the first cover of the capacitance sensor 5 and to the first input of the analog comparator of the microcontroller 1, the second cover of the capacitance sensor 5 is connected to a minus terminal of a source of power supply of the microcontroller 1, the first output of the thermistor 4 is connected to the second outputs of resistors 2 and 3, the second output of the thermistor is connected to the third output of the microcontroller 1, to the output of the first width-pulse modulator of the microcontroller 1 an input of the controlled source of reference voltage 6 is connected, the output of which is connected to the second input of the analog comparator of the microcontroller 1, the output of the second width-pulse modulator of the microcontroller 1 is connected to the first input of the analog comparator of the microcontroller 1.

EFFECT: expansion of functional capabilities of a microcontroller metering converter.

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Description

FIELD OF THE INVENTION

The invention relates to measuring equipment, in particular to devices for measuring the flow rate of gas or liquid by resistive heated sensors, and can be used in information-measuring systems for monitoring non-electrical quantities by resistive and capacitive sensors.

State of the art

If a resistive temperature sensor heated by a current is immersed in a gas or a liquid medium, then its temperature is determined by the thermal equilibrium mode between the amount of heat supplied to the sensor and transferred to the environment. The amount of heat given off by the sensor depends on the flow rate of the gas or liquid in which it is placed. If you measure the resistance of this sensor, as well as the current flowing through it, then you can determine the speed of the gas or liquid flow in which this sensor is located.

A device for measuring electrical capacitance and / or active resistance, comprising two one-shots, included in a ring circuit, a pulse generator and an indicator, capacitors are included in the timing circuits of the first and second one-shots, respectively, of the measured capacitance and reference, the generator output is connected to the start inputs of both one-shots, between the second outputs of the single vibrators an indication unit is included (see US Pat. RF No. 2099724, class G01R 27/26).

A disadvantage of the known solution is limited functionality, the device cannot be used to measure the flow rate of a gas or liquid.

A device for measuring non-electric quantities by capacitor sensors is known, which contains a microcontroller (MK), an indicator, first and second generators, during which the capacitive sensor and a reference capacitor are respectively connected, the generator outputs are connected to the MK inputs, the indicator is connected to one of the MK ports (see Patent of the Russian Federation No. 2214610, class G01 27/26).

A disadvantage of the known solution is limited functionality, the device cannot be used to measure the flow rate of a gas or liquid.

The closest in technical essence to the claimed technical solution and adopted by the authors for the prototype is a microcontroller device for measuring the shaft speed containing MK, an indicator, a capacitive sensor, a reference capacitor, two resistors. The first plates of the capacitive sensor and the reference capacitor are connected to the common wire, the second plates of the sensor and the reference capacitor are connected, respectively, to the first and second inputs of the analog comparator MK and to the first conclusions of both resistors, the second conclusions of which are connected to the outputs of the MK (see Pat. RF No. 2214610, CL G01 27/26).

A disadvantage of the known solution is limited functionality, the device cannot be used to measure the flow rate of a gas or liquid.

Disclosure of invention

The technical result that can be achieved using the present invention is to expand the functionality of the microcontroller measuring transducer, namely to measure the flow rate of gas or liquid.

The technical result is achieved by the fact that in a microcontroller measuring transducer of gas or liquid flow velocity containing MK, the first and second resistors, a capacitive sensor, the first and second resistors are connected by the first terminals respectively to the first and second outputs of the MK, the second terminal of the first resistor is connected to the first the capacitive sensor plate and to the first input of the MK analog comparator, the second capacitive sensor plate is connected to the negative terminal of the MK power supply, a thermistor and a control are introduced the reference voltage source, the first terminal of the thermistor connected to the second terminals of the first and second resistors, the second terminal of the thermistor connected to the third output of the MC, the input of the controlled reference voltage source connected to the output of the first pulse-width modulator MK, the output of the controlled reference voltage source connected to the second the input of the analog comparator MK, the output of the second pulse-width modulator MK is connected to the first input of the analog comparator MK.

Brief Description of the Drawings

Figure 1 presents the structural diagram of a microcontroller measuring transducer for the flow rate of gas or liquid.

The implementation of the invention

The microcontroller measuring transducer of the gas or liquid flow velocity contains (Fig. 1) MK 1, the first resistor 2, the second resistor 3, the thermal resistance 4, the capacitive sensor 5, the controlled reference voltage source 6, the first conclusions of the resistors 2 and 3 are connected respectively to the first and second MK 1 outputs, the second terminals of resistors 2 and 3 are connected to the first plate of the capacitive sensor 5 and to the first input of the analog comparator (not shown in Fig. 1) MK 1, the second plate of the capacitive sensor 5 is connected to the negative terminal of the power supply MK 1, the first terminal of thermistor 4 is connected to the second terminals of the first resistor 2 and second resistor 3, the second terminal of the thermistor is connected to the third output of MK 1, to the output of the first pulse-width modulator (PWM) (not shown in Fig.) MK 1 is connected the input of the controlled reference voltage source 6, the output of which is connected to the second input of the analog comparator MK 1, the output of the second PWM (not shown in Fig. 1) MK 1 is connected to the first input of the analog comparator MK 1.

A microcontroller measuring transducer of gas or liquid flow rate works as follows.

MK 1 puts the first and second outputs in a high-resistance state and connects the output of the first PWM to the first output of the thermal resistance 4. From the pulse current of the PWM signal, the thermal resistance 4 is heated. The power dissipated by the thermal resistance 4 is proportional to the duty cycle of the PWM signal of the second PWM. After some time, MK 1 transfers the output of the second PWM to a high-resistance state, which is equivalent to disconnecting it from the thermal resistance 4. MK 1 switches to the measurement mode of the thermal resistance 4. For this, MK 1 linearly increases the duty cycle of the output signal of the first PWM. As soon as the analog comparator changes the logic level at the output, MK 1 determines the voltage incident on the thermal resistance 4 from the fill factor of the output signal of the first PWM, and determines the thermal resistance 4, and therefore the gas flow rate.

To increase the accuracy of measuring the gas flow rate MK 1 determines the humidity of this gas by measuring the capacitance of the gas humidity sensor 5. The capacitance measurement is as follows.

MK 1 puts the first and third outputs in a high-resistance state, clears the built-in pulse counter, supplies a high voltage level to the capacitive sensor 5 through resistor 2, and starts the built-in pulse counter from the internal clock generator. As soon as the voltage at the capacitive sensor 5 exceeds the voltage at the second input of the analog comparator, the logic level will change at the output of the latter. Using this signal, MK 1 stops the counter in which a binary code will be generated proportional to the time constant τ of the charge of the capacitive sensor 5. Using the well-known expression τ = RC, MK 1 determines from the expression C = τ / R the capacitance of the capacitive sensor 5. Resistance R resistor 2 is known. Then MK 1 takes into account the influence of humidity of the controlled gas on the measurement of its flow rate and transmits the result via the built-in standard serial interface, for example, to a programmable logic controller.

If a fluid flow rate is measured, then MK 1 takes into account, using a special algorithm, the temperature of the controlled fluid.

Advantages of the invention: expanded functionality of a microcontroller measuring transducer, which allows you to measure the gas flow rate, its humidity or liquid flow rate.

Claims (1)

A microcontroller measuring transducer of gas or liquid flow velocity, comprising a microcontroller, first and second resistors, a capacitive sensor, wherein the first and second resistors are connected by the first terminals respectively to the first and second outputs of the microcontroller, the second terminal of the first resistor is connected to the first lining of the capacitive sensor and to the first input microcontroller analog comparator, the second capacitive sensor lining is connected to the negative terminal of the microcontroller power supply, which differs in that a thermistor and a controlled reference voltage source are introduced into it, the first terminal of the thermistor connected to the second terminals of the first and second resistors, the second terminal of the thermistor connected to the third output of the microcontroller, the input of the controlled reference voltage source connected to the output of the first pulse-width modulator of the microcontroller, output a controlled reference voltage source is connected to the second input of the analog comparator of the microcontroller, the output of the second pulse-width modulator the microcontroller is connected to the first input of the analog comparator of the microcontroller.