SU870945A1 - Thermal flowmeter - Google Patents

Description

I

The invention relates to the field of measurement technology, namely, devices for measuring the flow rate of liquids and gases.

Devices for measuring the flow of liquids and gases are known, which contain temperature-sensitive elements based on the dependence on the rate (flow rate) of the heat transfer flux of the primary transducer (heated body) placed in the controlled flow}.

Of the known devices, the closest device is a flow measurement device containing a measuring section of a pipeline with measuring and compensating temperature-sensitive elements located on it, which are in different hydrodynamic conditions, to the outputs of which are connected in series AC amplifiers, frequency controlled oscillators and pulse shapers 2.

However, the known flow meter does not accurately measure flow rates with sharp fluctuations in the temperature of the controlled medium.

The purpose of the invention is to improve the measurement accuracy.

This is achieved by the fact that in a heat flow meter containing a measuring section of a pipeline with measuring and compensating temperature-sensitive elements located on it, which are in different hydrodynamic conditions,

IS to the outputs of which are connected in series AC amplifiers, control frequency generators and pulse shapers, at the output of the measuring circuit

20 an indicator device is connected, temperature-sensitive elements are made in the form of pyroelectric thermal sensors, and the main and auxiliary LEDs, a calibrated pulse generator, a time interval generator, a counter with a decoder and a frequency divider, the main LEDs, a calibrated pulse generator and a time interval generator are connected in series to the measuring circuit and connected to one of the meter inputs, the frequency divider is connected between the output of the generator controlled by The pulses of the measuring thermosensitive element, to the output of which one of the auxiliary LEDs is connected, are connected to the output of the pulse former of the compensating thermosensitive element, two series-connected LEDs are connected, and a counter with a decoder is connected between the output of the controlled frequency generator and the input of the indicating device. The drawing shows the functionality of the described thermal flow meter flow meter. The heat flow meter contains a measuring section of pipeline 1, a calibrated sleeve 2, measuring and compensating temperature-sensitive elements, filled in the form of pyroelectric thermal sensors 3 and 4, amplifiers of alternating current 5 and 6, controlled frequency generators 7 and 8 pulse formers 9 and 10, base 1 1. and 12 and auxiliary 13 and 1

LEDs, a generator of calibrated pulses 15, a driver of time intervals 16, a counter 17, a frequency divider 18, a decoder 19, an indicator device 20.

The device works as follows.

The device is calibrated at extremely low operating pressure, extremely high medium temperature and no high-speed flow. Pyroelectric flow sensors 3 and 4 are used in a dynamic mode of operation. They excite thermal oscillations with amplitude M around a certain temperature T (overheating temperature}. The sources of heat pulses are the light fluxes of the main LEDs 11 and 12, excited by a generator of calibrated pulses 15.

When the pressure and temperature deviate from the initial values of heat

the measuring circuit of the automatic temperature control of the temperature-sensitive element 3 is chosen in such a way that at

 overheating temperature equal to T and T + DT, the beam feedback circuit of the LED 13 is opened and the temperature mode of the temperature-sensitive element 3 continues to be determined

5 only thermal power supplied to it from the LED 14.

The device also ensures that the conditions of temperature and velocity invariance of the measuring and compensation contours are met. They are mainly reduced to ensuring equality of transfer functions of thermosensitive elements 3 and 4 in terms of temperature pulsations and

Claims (2)

55 flow rates. To this end, identical sensors for heat exchange with the flow of the controlled medium are provided for both sensors. Structurally, this 54th exchange of temperature-sensitive elements 3 and 4 is intensified. As a result, they generate an alternating voltage at the terminals of their electrodes, which is amplified by alternating current amplifiers 5 and 6. The amplified voltage is converted by controlled frequency generators 7 and 8 into proportional frequency values, which are fed to the inputs of shapers 9 and 10 pulses, at compensatory directly, and that of the measuring device, through the frequency divider 18. The output pulses of the pulse formers 9 and 10 excite the auxiliary LEDs 3 and 14, the thermal power of the light fluxes of which is equivalent to In terms of the LEDs 13 and 14, they will work as described above, only when the operating mode of operation is reached. Due to the fact that the LED 13 irradiates only the sensor element 3, and the LEDs 14 irradiate simultaneously the sensors 3 and 4, then the working temperature points of the temperature-sensitive elements 3 and 4 are shifted by the measuring device to the T + LT position, and those of the compensation one - to the T position - DT and will be further stable fluctuate within these limits until the moment of a speed flow. The operation mode is achieved by making the working channel of the measuring section 1 in the form of two branching sections of the pipeline, in which the measuring and compensating temperature-sensitive elements 3 and 4 are located, which are washed away in a controlled flow. As a result, both temperature-sensitive elements will react equally to pulsations of the flow velocity, and for changes in its temperature and pressure. In order to extract information about the flow rate, it is necessary and sufficient that the cjcopocTb flow washing the measuring thermoelectric Valve element 3, other than the flow rate, washing the compensation thermosensitive element 4. This condition is ensured by installing a pipeline with a compensating temperature element calibrated in Tule 2 at the beginning of the branch branch, the split ratio of the flow between two branching branches is regulated by the choice of the passage section bores of the sleeve 2. When the flow rate is reached, the heat exchange of both thermosensitive elements is intensified even more. Due to the presence of a difference in the flow rates, the heat removal from the temperature-sensitive element 3 will exceed the amount of heat supplied to it from the LED 14. As a result, the operating point of the temperature-sensitive element 3 will shift to the T-LT region, the beam feedback will be closed through the LED 13 and at the generator output the controlled frequency 7 is in accordance with the sequence of pulses, the frequency of which will be proportional to the difference in flow rates in both nozzles. To maintain the set position or operating point on the volt-temperature characteristic of the temperature-sensitive element 3 (overheating value), it is necessary that the frequency of the pulses formed at the output of frequency divider 18 be proportional to the value of the flow difference. At the same time, the frequency of the pulses on the device’s output, and consequently, at the input-frequency divider 18, should be proportional to the total flow rate of the controlled flow through the measuring section 1, the division factor of the frequency divider 18 is selected, and the calculation of these two conditions. f Usually, to obtain information on the output of the device directly in terms of flow rates, without using special conversion tables, it is necessary that the sensitivity coefficient of both temperature-sensitive elements 3 and 4 be equal to each other and equal to a certain value. However, in general, this requirement is not fulfilled. Dip expansion of the allowable range of variation of the values in the device uses the unit for forming time intervals 16, using for its operation the frequency of the generator of calibrated pulses J5. Changing the temperature of the temperature-sensitive element 3 during its operation leads to a proportional change in the voltage on the outputs of its Electrodes by the value of DO S1bdT where about is the temperature coefficient of voltage of the Thermosensitive elements - pyroelectric thermal sensors. This voltage increment is converted by a controlled generator. frequency 7 in proportion to the frequency change f, which (taking into account the division factor of the frequency divider 18) is fed to the counting input of the counter .17. From the time interval generator, a signal is sent to the control input of the counter allowing the counting to be on time) / of K where K t is the measurement discreteness of the flow rate, equal to 1; 0.1; 0.001 l / h. The time interval of measurement is established depending on the value of the temperature coefficient of voltage of the temperature-sensitive element. In this case, the counter counts a pack of pulses, the number of which is equal to the value of t (time). This code representation by the counter 17 of the received information is decoded by the decoder 19, the result is indicated in units of the approach by the indicator device 20. The duration of the irradiation pulses is chosen less than the constant heating time of the temperature-sensitive elements, the temperature of the latter is determined by the average frequency of irradiation. The transfer of the device from one bottom of it to the measured flow rate to another can be carried out by replacing sleeve 2 with another with the necessary cross-section of the through-hole. The diodes used in the proposed device operate in pulsed I mode and their radiation stability can be improved by supplying them from a pulse former operating alternately at predetermined intervals in current generator and voltage generator modes. In this case, the temperature-sensitive element will be the average size of the unit of the radiant flux of LEDs. The use of pyroelectric thermal sensors as thermosensitive elements made it possible, on the basis of their extremely high resolution, to improve the functional and metrological capabilities of the device. Napo, they, jre require food, which allows them to isolate; E) ZOVat in portable and special. devices, and devices based on them are characterized by low energy consumption. The high sensitivity of pyroelectric thermal sensors reduces the temperature of their overheating to several degrees and uses low-power heat sources for this purpose, for example, electric diodes. Moreover, the high sensitivity of pyroelectric thermal sensors allows using the device not only to measure flow, temperature, pressure, but also concentration when analyzing mixtures and registering very low rates of temperature measurement, and, consequently, the flow rates are practically unattainable for each other. their thermoelectric environments. Since the relative error of the described measuring device is related to sensitivity, inversely proportional to dependence, not only the measurement sensitivity increases, but also the measurement error decreases accordingly. Claims of the invention A heat flow meter containing a measuring section of a pipeline with measuring and compensating thermosensitive elements located on it, which are in different hydrodynamic conditions, to the outputs of which are connected in series AC amplifiers, controlled frequency generators and pulse shapers are connected to the output of the measuring circuit An indicator device, characterized in that, in order to improve measurement accuracy, temperature-sensitive elements performed in the form of pyroelectric thermal sensors, and the main and auxiliary LEDs, the calibrated pulse generator, the time interval former, the counter with the decoder and the frequency divider, the primary LEDs, the calibrated pulse generator and the time interval former, are connected in series and connected to one of the inputs. the counter, the frequency divider is connected between the output of the controlled frequency generator and the input of the pulse shaper of the measuring thermostat ity of the element, which is connected to the output of one of the auxiliary LEDs to the output pulse shaper compensation temperature sensing element two series-connected LEDs are connected and COUNT; with the decoder is connected between the output of the controlled frequency generator and the input of the indicator device. Sources of information taken into account during the examination 1. Korotkov PA Heat flow meters. L., Mechanical Engineering, 1969.. 2. USSR author's certificate number 639314, cl. G 01 f 1/00, 1978 (prototype).