SU1582014A1 - Apparatus for measuring flow rate of gas - Google Patents

Abstract

The invention relates to the field of instrumentation and is intended to measure low gas flow rates. The aim of the invention is to expand the measuring range of a flow meter. The electronic circuit compares the transfer time of the label from generator 2 to the first thermistor 3 with the threshold value set, and if the transfer time is longer than this value, the label is recorded by the first thermistor 3, if the transfer time is less than the threshold value, the label is registered with the second transfer time tag is set by the pulse duration of the one-shot 19. In order for the flow meter's calibration characteristic to remain unchanged when registering the mark with the first 3 or second 4 thermo resistors ohm, a device introduced divider circuit 20 with the frequency dividing factor equal relative distances respectively from the second and the first 4 to 3 thermistors generator 2 tag. 3 il.

Description

FIG. one

The invention relates to instrumentation and can be used to measure low gas flow rates.

The purpose of the invention is to expand the measurement range.

Figure 1 shows the flow chart of the flow measurement device; FIGS. 2 and 3 are time diagrams of the device operation at small and large flow rates, respectively. The flow meter consists of the housing of the flow meter 1, the generator 2 thermal labels, the first 3 and second 4 thermo resistors, the first 5 and second 6 resistors, amplifier 7, rectifier 8, polarity determiner 9, extremator 10, first 11 vibrator, first 12 and the second 13 elements 3 And, the trigger 14, the second element 2 1MLI 15, the third one-oscillator 16, the second one-oscillator 17, an impulse amplifier 18, the fourth one-oscillator 19, the frequency divider 20 and the first element 2ILI 21.

When measuring small values of flow, the device operates as follows (see figure 2).

When the device is put into operation, the one-shot 16 produces a short pulse, which is amplified by the pulse amplifier 18, and the generator 2 forms a thermal tag. The label is carried by the flow and is carried out. short-term heating of the thermistor 3, the unbalanced bridge signal with a positive polarity passes through the amplifier 7 and is fed to the polarity determiner 9, which is set to the signal limiting mode at a positive level. On the leading edge of the signal at the direct output of the polarity detector 9, the one-shot 17 is activated and switches the trigger 14 to the zero-state. The signal at the output of the rectifier 8 repeats the signal from the output of the amplifier 7, and the top of the wave corresponds to the passage of the label core through the thermostat 3. When the output signal reaches an extremum, the output of the extremator 10 generates a logical 1 signal and a one-shot 11 gives a short pulse,

Simultaneously with the start of the thermal tag by the generator 2, the one-vibrator 16 is triggered on the leading edge of the pulse of the single vibrator 16 and generates a pulse signal O, the duration of which determines the threshold value of the transfer time of the mark from the generator to the receiver, at which the tag is recorded by the first 3 or second 4 thermistors. If the pulse O from the output of the one-shot 19 ends before the moment of

tag marking, signal 1 from the output of the one-shot 19 and signal 1 from the direct output of the detector 9 polarity, element 3 AND 12 is prepared to pass a pulse from the output of the one-shot 11 to the S input of the trigger 14. At this, the signal Z is closed with signal O from the inverse determinant 9 polarity. When registering a tag, a pulse from the one-shot output

0 11 passes through the element ZI 12 to the S input of the trigger 14 and translates it into a single state. On the leading edge of the signal from the direct output of the trigger 14 that passes through the element

5 2 OR 15, the one-shot 6 is triggered, and its pulse applied to the input of the pulse amplifier 18 triggers the next tag. The signal About with inverse trigger output 14

0 it is prohibited to pass the signal through the element ZI 13. With the arrival of the next label, the device operation cycle is repeated.

When measuring large values of the flow, when the time of transfer of the label from the generator to the first thermistor 3 is less than the duration of the pulse of the single-vibrator 19, the device works as follows (see Fig. 3)

0 Similarly to the previously described, the heat label performs a temporary heating of the thermistor 3, the signal from the output of the amplifier 7 determines the polarity 9

5, the signal limiting state at the positive level and on the leading edge of the signal at its direct output triggers the one-shot 17, the trigger 14 turning into the zero state. Q At the time of the extremum of the tag registration signal, the one-shot 11 produces a short pulse that goes to the first inputs of the ZI 12 and 13 elements. However, the ZI 12 element is closed by a 0m pulse from the one-shot 19 output, and the ZI 33 element is closed by the O signal from the inverse output of the determinant 9 polarities. Thus, if the transfer time

five

51

the tags from the generator to the first thermistor resistor 3 are less than the duration of the pulse O from the output of the one-shot 19, the device does not register the passage of the mark through the first thermistor 3. The heat label moves further along the sensor channel and provides a brief warm-up of the second thermistor 4, the bridge unbalance signal, having a negative polarity, passes through the amplifier

7 and sets the polarity determiner 9 to the signal limiting mode at a negative level. Straightener

8 changes the polarity of the input signal to a positive one, similarly to the extremator 10 described earlier and a single vibrator 11, form a short-term impulse at the moment of passage of the mark core. This pulse passes through the open element ZI 13, element 2ILI (5 at the input of the continuous vibration 16, which generates a pulse to start the next mark. With the arrival of the next mark, the cycle of the device repeats.

The repetition rate of tags when they are registered by the first thermistor is determined by the formula

four

L sl

(ABOUT

where Q - consumption rasaj

S - section of the internal channel

flow meter;

L-) is the distance from the tag generator to the first thermistor.

The repetition rate of the tags when they are registered by the second thermistor is determined by the formula

„„ 3sl

(2)

where LЈ is the distance from the tag generator to the second thermistor.

In order to obtain an unbroken calibration characteristic of the flow meter, the device’s output signal should be followed by the frequency of the tags when they are recorded by the second thermistor and the frequency of the tags divided by the coefficient

 H L,

first thermistor. In the device diagram, this operation is carried out

fenient Kdel

at their register

146

with a node containing a frequency divider 20 with a Kdel division factor

 - and element 2ILI 21. When measuringLV

low gas flow rates, when the tags are recorded by the first thermoreistor, the pulses from the output of the ZI element 12, pass through the divider 20 and the element 2ILI 21, are output to the device and the frequency of the output pulses

(3)

15

When measuring large gas flow rates, the pulses from the output of element 3 and 13, having passed through element 2IL or 2), are fed to the input of the device and their frequency is equal to

f & - i-i}

 -9

SL,

(four)

five

0

five

0

five

0

five

Thus, the calibration characteristic of the flow meter does not change when the label is registered with the first or second thermistor.

Claims (1)

Depending on the lower and top-hero limits of the measured flow rate, as well as the properties of the gas whose flow rate is measured, select the required distances Lt, L and the pulse duration of the one-vibrator 19. I Invention A device for measuring gas flow, containing a thermal tag generator, connected to a pulse amplifier, a bridge circuit, the shoulders of which are the first and second resistors, and the first and the first thermistors placed in the flow, an amplifier connected to the diagonal of the bridge, the output of which is connected in series with a rectifier, an extremer and the first one-shot, and a polarity determinant connected to the output of the amplifier, which is characterized by the fact that, in order to expand the measurement range, the first and second elements are entered into it, the second, third and fourth one-shot, the first and second elements OR, RS-trigger and frequency divider, and both thermistors are located on one side of the label generator in the direction of flow, with the first inputs of the first and second 715 elements I are connected to the output of the first one-shot, the second inputs are respectively to the direct and inverse outputs of the polarity determiner, the input of the second one-shot is connected to the direct output of the polarity determiner, and its output is to the R input of the RS-trigger, the output of the first And element connected to the S-input RS trigger and to the input of the frequency divider, the first to enter | elements OR are connected respectively with the output of the frequency divider and 149 direct output of the RS flip-flop, their second inputs are connected to the output of the second element AND, the outputs of the first element OR are the output of the device, and the output of the second element OR through the third one-shot is directly connected to the input of the pulse amplifier And through the fourth one-oscillator; the third input of the second element I is connected to the inverse output of the RS flip-flop.