Design and application of the hottest pulse flow s

2022-08-16
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Design and application of pulse flow sensor verification instrument

the verification of the instrument coefficient of traditional pulse flow sensor is generally completed by the volumetric flow standard device, counter and timer, as shown in Figure 1. Its instrument coefficient is defined as the number of pulses sent by the sensor when the fluid volume per unit volume passes through the flow sensor, and the unit is usually 1L (pulses per liter) or 1m3 (pulses per cubic meter). According to the provisions of literature [1], in order to ensure the effectiveness of the meter coefficient of the flowmeter, it is generally necessary to ensure that the absolute value of the relative error of the number of pulses output by the flowmeter in a verification is not greater than 13% of the repeatability of the flowmeter being tested. Since the counting error of the general counter is one pulse, within the verification time interval (the time t between two control pulses in Figure 1), the counter should collect enough pulses n to achieve the required verification accuracy

Figure 1 Calibration diagram of instrument coefficient

for some large-diameter flow sensors, the instrument coefficient is generally small (for example, the instrument coefficient of 200 turbine flowmeter is only 1.5/l; the instrument coefficient of large-diameter vortex flowmeter is lower, only about 0.2/l). For such a flowmeter, it is necessary to collect enough pulses. First, it takes a long time to calibrate, and second, it is necessary to have larger calibration equipment (larger standard containers). Due to various restrictions, the counting pulse can not meet the requirements. The dual time counting technology is a relatively general pulse interpolation technology in the world at present. It can use a small volume of verification equipment in a short verification time, and can still ensure sufficient technical accuracy when the total number of pulses is small. It was earlier applied to the micro volume tube flow standard device

the pulse flow sensor calibrator we developed is a dual time method calibrator composed of traditional counter and dual time method measurement and control technology. The test shows that the verification instrument is convenient and reliable, can shorten the verification time, use a smaller standard container to verify a larger diameter flow sensor, and has higher technical accuracy than the conventional verification method

1. Double time counter principle

pulse interpolation technology is an effective way to increase the output signal resolution of the piston calibration device by configuring the servo oil source with imported high-pressure gear pump and servo flowmeter, so as to reduce the volume of the calibration device. Generally, in order to get enough pulses for calibrating the flow meter, two ways can be taken: one is to improve the output signal resolution of the flowmeter, so that as many pulses as possible can be obtained within the limited calibration time; The second is to increase the effective volume of the calibration device. Generally, the number of pulses output by a unit volume of fluid through the flowmeter is limited (such as the turbine flowmeter and vortex flowmeter above), and the effective volume of the calibration device cannot be too large. Pulse interpolation technology solves this problem well. It has several methods, such as double time method, four time method and phase-locked loop method. By using a small volume (the effective volume of the device) to collect 500 pulses, the piston calibration device can achieve the same accuracy as the large volume calibration device to collect 10000 pulses

Figure 2. The principle of double time method is shown in Figure 2A. When the flow pulse signal period is stable, the pulse interpolation number is

(1)

, where: n is the number of flow sensor signal pulses recorded by the counter; N1 is the number of pulses interpolated by double time method or four time method; T1 is the time interval from detecting the start signal to detecting the stop signal; T1 is the whole pulse cycle time interval from the rising edge of the first pulse after detecting the start signal to the rising edge of the first pulse after detecting the stop signal

when the stability of the flow standard device meets the provisions of the standard procedures, the flow pulse signal cycle can be considered to be stable, so the pulse interpolation number obtained by equation (1) should be effective

in addition to the double time method, the four time method can also be used to determine the number of pulse interpolation. The four time method measures four times T1 ~ T4, as shown in Figure 2B. The pulse interpolation number is

n1=n + (2)

this paper takes the double time method as an example to design a pulse flow sensor calibrator

2. Hardware design of the calibrator

the hardware principle block diagram of the pulse flow sensor calibrator is shown in Figure 3

Figure 3 hardware principle block diagram of dual time flow calibrator

② verify with standard frequency signal generator, and the results are listed in Table 2

Table 2 results of calibration with standard frequency signal generator

③ the calibrator has been used to calibrate the instrument coefficient of turbine flowmeter and achieved good results

the calibrator does not use microprocessor and has good working reliability. The control signal can use the single pole double throw switch K1 to select a very narrow pulse signal or a level signal. When controlled by level signal, switch K2 can be used to select high-level control or low-level control

when the control signal is a pulse signal (the first control signal in Figure 3), switch K1 selects pulse control, sets the q-end output of the initial state trigger Tr1 as low level L (assuming that the output of high level H is also irrelevant), and outputs high level H to feed back to d-end. Switch K2 selects high-level control or low-level control

when the control signal is a pulse signal (the first control signal in Figure 3), switch K1 selects pulse control, sets the q-end output of the initial state trigger Tr1 as low level L (assuming that the output of high level H is also irrelevant), and outputs high level H to feed back to d-end. Switch K2 selects high-level control (if the q-terminal output of the initial state trigger Tr1 is high-level h, K2 can select low-level control). The input terminals of NAND gates B and C and the d-terminal of trigger TR2 are low-level. Therefore, gates B and C are closed, and the q-terminal output of trigger TR2 must also be low-level under the action of flow pulse signal, and gate e is closed. The counter and timers T1 and T2 are both in the stop state. Use the reset button to return the counter and timer to the initial zero state and display all zeros

when the start counting control signal pulse (the first control pulse) arrives, Solvay TORLON and spire superperformance polymers used in these fields also have more advantages than the d-end of Tr1 is high level h. therefore, the control pulse triggers Tr1 to make its q-end output high level H, and immediately opens NAND gates B and C to make the counter and timer T1 start counting and timing. At this time, the NAND gate E has not been opened, but the d end of the trigger TR2 has been at a high level. The rising edge of the first flow signal after the leading edge of the control signal triggers TR2, causing its Q end to output a high level and open the NAND gate e, and the timer T2 also starts timing

when the stop counting control signal pulse (the second control pulse) arrives, Tr1 is triggered again to make the Q end output low level L, so as to immediately close the NAND gates B and C, and make the counter and timer T1 stop counting and timing. However, the NAND gate e is not closed immediately, but the rising edge of the first flow signal after the front edge of the stop counting control signal pulse can trigger TR2 and output low level L, and close the NAND gate e to stop the timer T2. By substituting the data obtained from timers T1 and T2 into equation (1), a more accurate pulse interpolation number can be obtained

when the control signal is a level signal (the second and third control signals in Figure 3), switch K1 selects level control, which is equivalent to directly controlling NAND gates B and C and the d end of trigger TR2 across trigger Tr1. The selection switch K2 points to high-level control or low-level control respectively for high-level action or low-level action. Other actions are exactly the same as pulse control

3, indicators and results

3.1 indicators of the calibrator

in addition to the above as a controllable counter and timer, the calibrator also has the function of measuring signal frequency and cycle. It is not used to verify the flowmeter, but can be used as an instrument to measure the signal frequency or cycle

specific indicators are as follows:

① timer, 6-bit LED display, resolution of 1ms

② timer (including frequency and cycle), 8-bit LED display, the highest resolution is 1Hz, the cycle is 0.1 s, and the count is 1 pulse

③ measurement range: the frequency is 10Hz ~ 100MHz, the cycle is 0.5 s ~ 10s, the counting capacity is 99999 999, and the timer is 1ms ~ 999.999 s

④ T1 and T2 switch display manually

3.2 the deeds of leading paper enterprises in 2018 are unsatisfactory. Test results

① using 51 series microprocessor to output periodic square wave signals, the influence number of different stress states on material strength and plasticity can be analyzed as the standard calibration frequency and periodic measurement. The results are listed in Table 1

Table 1 calibration results using periodic square wave as standard

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