JPS63131027A - Ultrasonic gas flowmeter - Google Patents

Abstract

PURPOSE:To perform measurement with good accuracy, by calculating the respective propagation times in forward and reverse directions or the sum of the reciprocals thereof and performing operation from the coefficient based on the ratio of the calculated value and predetermined reference temp. CONSTITUTION:An ultrasonic wave is changed over in its propagation direction by a forward/reverse change-over circuit 31. The count data obtained by a counting unit 4 is subjected to moving averaging processing in an averaging unit 6 and the operational processing of a flow rate is performed by a flow rate operation unit 7. A temp./pressure converting unit 8 performs conversion operation for converting the flow rate obtained by the unit 7 to the value in a predetermined standard state. That is, the relation between the respective propagation times of the ultrasonic wave in forward and reverse directions or the sum of the reciprocals thereof and the temp. of gas in a measuring state is stored in a memory 82. Then, the coefficient based on the ratio of the temp. of the gas outputted from a memory 82 on the basis of the respective propagation times or the sum of the reciprocals thereof and predetermined reference temp. is operated along with the measured flow rate value by a temp. converting circuit 81 to be converted to the measured flow rate under the reference temp.

Description

Detailed Description of the Invention: a. Industrial Application Field The present invention relates to an ultrasonic gas for measuring the flow rate of gas flowing in a pipe using ultrasonic waves, and in particular for converting it into a reference temperature state for measurement. Regarding flowmeters.

b. Prior Art Devices that propagate ultrasonic waves in gas flowing inside a pipe and measure the flow velocity and flow rate of the gas inside the pipe by utilizing changes in the propagation speed are conventionally known. For example, a pair of probes for transmitting and receiving ultrasonic waves is installed diagonally opposite each other on the peripheral wall of a flow tube, and the probes transmit and receive ultrasonic waves alternately in the forward and reverse directions relative to the flow. There is a method of measuring the flow velocity of the fluid in the pipe by determining the difference in the propagation time (or its reciprocal) in both the forward and reverse directions of the ultrasonic waves propagating across the flow pipe.

Conventionally, with such current meters, various measures have been taken to ensure that the measured values are not affected by the temperature of the measured fluid (for example, by taking the difference in the reciprocal of each propagation time, the effect of the sound speed in the fluid is removed. However, this is only an attempt to accurately determine the flow velocity and flow rate under measurement conditions.

On the other hand, the gas flow rate varies depending on temperature and pressure even if the flow rate is the same, so the flow rate obtained here is generally used as the standard temperature,
It is customary to convert the pressure to standard pressure and output or display it. For this reason, in conventional ultrasonic gas flowmeters,
In addition to the current meter, a temperature transmitter and a pressure transmitter are provided, and the output signals of the current meter are normalized using the temperature and pressure output signals to determine the gas flow rate in the standard state.

C1 Problems to be Solved by the Invention However, in the conventional ultrasonic gas flowmeter, when actually installing the transmitter, there is relatively little error in pressure due to differences in measurement points, and it is difficult to use an ultrasonic flowmeter. Considering that the flow pipe to be installed has a certain straight pipe length, this is not a big problem, but the other temperature is difficult to install the current meter probe and the detection end of the temperature transmitter in the same place. , it is inevitable that there will be some discrepancies, and there has been a problem that accurate normalization calculations are difficult.

The present invention has been made in view of the above, and its purpose is to solve the above-mentioned problems, and to correct the temperature in the normalization calculation when measuring the flow rate of gas. An object of the present invention is to provide an ultrasonic gas flow meter that can derive the temperature at that time from , automatically calculate the flow rate at a standard temperature based on this, and measure the flow rate with high accuracy.

d. Means for Solving the Problems The structure of the present invention for achieving the above object is such that the wall surface of the gas flow path is provided with a structure in which the wall surface of the gas flow path is diagonally to the longitudinal direction of the flow path.
Alternatively, a pair of ultrasonic transducers that face each other to transmit and receive ultrasonic waves from diagonal directions is installed, and the ultrasonic waves propagate in the forward and reverse directions of the gas flow, thereby reducing the ultrasonic waves propagating in the flow path. In a flow meter that measures the flow rate of gas based on the difference between the respective propagation times in the forward and image feeding directions or the respective reciprocals, measurement is made as the sum of the respective propagation times or the respective reciprocals of the ultrasonic waves in the forward and reverse directions. storage means storing the relationship between the temperature of the precursor gas in the state, and the ratio of the temperature of the gas outputted from the storage means by the sum of each of the propagation times or the reciprocals thereof and a predetermined reference temperature; The present invention is characterized by comprising temperature conversion calculation means for calculating a coefficient based on the flow rate measurement value measured as described above and converting it into a flow rate measurement value at a reference temperature.

e. Operation First, the principle of operation of the present invention will be explained. As shown in FIG. 1, the inner diameter of the flow tube 1 is d, and the transducers 21, 22, . , the angle between the axes of the transducers 21 and 22 and the tube axis is θ, the sound velocity of the gas is 02, and the flow velocity is The propagation time t2 when propagating in the opposite direction to the flow is 1,
, 1. From the difference in the reciprocals of , the flow velocity V is 2 cos 6 t, t.

Therefore, the flow rate q is The temperature and pressure at the time of this measurement are T, P, and the temperature in the standard state.

When the pressure is T□P, the flow rate qn in the standard state is as follows. Ta\'LK. / is the compression coefficient ratio. on the other hand,
The sound speed C of the gas is found by Since C is generally a function of temperature T, C
= f (T), and by finding T=f-'(C), the temperature T can be found from C. Therefore, by applying more pressure P, the flow rate q in the standard state can be reduced.
1 can be found.

By the way, if we think about air (T is ', C is m/
s), t+ tz The third term in the above equation is calculated from the measured value of (1/l+ +1/lz), but the calculation requires a long measurement time.

Since the temperature range in a normal plant is limited, the relationship (table) of T to (1/l+ + 1/lz) is stored in advance in ROM, and (1/t+ +
1/tz).

f. Examples Hereinafter, preferred embodiments of the present invention will be described in detail by way of example based on the drawings.

FIG. 1 is a block diagram of an ultrasonic gas flowmeter showing an embodiment of the present invention, and FIG. 2 is a time chart illustrating the operation of each part of the flowmeter. In both figures, a forward/reverse switching circuit (SW
) 31 is a timer (TM) that operates based on the clock pulse generator (CPG, ) 51 of the timing unit 5'.
52's output F (FIG. 2A) to switch the propagation direction of the ultrasonic waves. The transmitted wave T (Figure 2) is transmitted by a timer (TM
) 52, the signal is generated from the transmitting circuit (TX) 32, passes through the forward/reverse switching circuit (SW) 31, and is applied to the transmitter 21 (or 22). Here, it is converted into ultrasound and the ultrasound is sent out into the gas. Receiver 22 (or 21)
The ultrasonic signal received by
Enter 3. The receiving circuit (RX) 33 amplifies this electrical signal to a predetermined level and sends it to the comparator circuit (COMP) 34 (FIG. 2C). In the comparison circuit (COMP) 34,
This received wave is converted into a reference voltage V built in the transmitter/receiver unit 3.
t, and when a received wave larger than VT arrives, the output pulse is output to the flip-flop circuit (FF) of the counting unit 4.
41.

This flip-flop circuit (FF) 4 of the counting unit 4
1 is set by a transmission command signal from the timer (TM) 52 and reset by an output pulse from the comparator circuit (COMP) 34. Flip-flop circuit (FF) 4
The output of the counter (CNT) 43 is held at the level I for a time corresponding to the propagation time tu or t4 of the ultrasonic wave (Fig. 2, 2).
While the output of CPGI 1 is at H level, the clock pulses from the clock pulse generator (CPGI) 51 are counted through the AND gate 42. In this way, the counter (CNT) 43 of the counting unit 4 operates at time 1 according to the forward/reverse flag signal F.
．． ．． 1. is counted, and immediately after counting is completed, the counted data is sent to the averaging unit 6.

Averaging unit 6 is a clock pulse generator (CPG2)
61, Inter-y Nice (IF) 62. It consists of an averaging circuit (AVR) 63°, a memory (M, ) 64, and an interface (IP) from the counter (CNT) 43.
) 62 to calculate the moving average value of each arbitrary number of count data at times tl and tz given through step 62. That is, when new counting data is given from the counter (CNT) 43, it replaces the oldest data among the data stored in the memory (Ml) 64 and calculates the average value (FIG. ). The average values are processed independently at times tl and tZ and stored in the memory (Ml) 64. When this averaging process is completed, the next flow rate calculation unit 7 performs a flow rate calculation process based on this average value. That is, as shown in FIG. 2, in the moving average processing and flow rate calculation process, when new count data is obtained, the moving average process is immediately performed in the averaging unit 6, and when this process is completed, the flow rate calculation unit At step 7, flow rate calculation processing is started, and this processing is executed until the next new count data is given.

The flow rate calculation unit 7 consists of a flow rate calculation circuit (FLW) 71 and a memory (Mri 72).
1 is a circuit that calculates the flow rate using the above formula (4),
Memory 0+z)? 2 is the above d, cos θ, and L
Store constants and coefficients such as

The temperature/pressure conversion unit 8 is a conversion unit for converting the flow rate obtained by the flow rate calculation unit 7 into a value in a predetermined standard state, and performs temperature and pressure conversion calculations according to equation (7) above. be done. The conversion unit 8 includes a temperature conversion circuit (TMP) 81 and the (1/
ll + 1/12) and temperature T as a numerical table, and a pressure conversion circuit (PRS).
83, a memory (M,) 84 for setting pressure conversion coefficients, and a changeover switch 85. The changeover switch 85 is
This is a switch that selects whether the pressure conversion operation is performed automatically using a coefficient set within the flowmeter body, or whether the pressure conversion operation is performed using the output from an external pressure transmitter (PT) 10.

For a measurement target with relatively small pressure fluctuations, the selector switch 85 is set to the internal (memory M4) side, and pressure conversion is performed using a predetermined pressure value (constant value). Reference numeral 9 denotes a display (DIS) for displaying, integrating, etc. the output flow rate measurement value. Pressure transmitter (PT) 1
0 is a transmitter for detecting the pressure of the object to be measured as described above, and if this output is used, pressure conversion is performed based on the pressure in the measurement state.

The above flow rate calculation and temperature/pressure conversion calculation are not completed in just one period (G) in Figure 2, but are executed over multiple periods as shown in Figure 2 (H).In other words, the flow rate measurement value Q7 is In the same figure, (Σt,), i.

(Σta) calculated from n-=, and each time the flow rate output is obtained, based on the new moving average value of time t+, tg,
Execute flow rate calculation.

The above explanation has given an example of calculating the flow velocity and sound velocity based on the reciprocals x/l+ and t/lz of the propagation time in the forward and reverse directions of the ultrasonic wave, but the difference and sum of the propagation time LI+5, or t+, Convert tz to a frequency proportional to each,
It is also possible to calculate the flow velocity and sound velocity from their difference and sum. Furthermore, the above calculations can also be executed by a microcomputer.

It should be noted that the technology of the present invention is not limited to the technology in the above-mentioned embodiments, and means of other modes that perform the same function may be used, and the technology of the present invention can be modified in various ways within the scope of the above-mentioned configuration. It is possible to add.

g1 Effects of the Invention As is clear from the above explanation, according to the present invention, when measuring the flow rate of gas, ultrasonic waves are propagated in the forward and reverse directions with respect to the gas flow, and the respective propagation times or their reciprocals are The temperature in the measurement state is derived from the relationship between this sum and a predetermined gas temperature, and the flow rate at the standard temperature is calculated based on this, so a separate temperature transmitter is required. Since the temperature at the flow rate measurement position can be estimated, the gas flow rate can be measured with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an ultrasonic gas flowmeter showing an embodiment of the present invention, and FIG. 2 is a time chart illustrating the operation of each part of the flowmeter. DESCRIPTION OF SYMBOLS 1... Flow tube, 3... Transmission/reception unit, 4... Counting unit, 5... Timing unit, 6... Averaging unit, 7... Flow rate calculation unit, 8... Temperature/ Pressure conversion unit, 10... Pressure transmitter (PT), 2L22... Transducer/receiver, 71... Flow rate calculation circuit (FLW), 72... Memory (M2), 81... Temperature conversion circuit (TMP), 82...Memory (Mff),
83...Pressure conversion circuit (PRS), 84...Memory (M4), 85...Selector switch.

Claims (1)

[Claims] A pair of ultrasonic transducers that transmit and receive ultrasonic waves oppositely in a diagonal direction with respect to the long axis direction of the gas flow path or from an oblique direction are disposed on the wall surface of the gas flow path. In a flowmeter that propagates ultrasonic waves in the forward and reverse directions and measures the flow rate of gas based on the difference between the propagation times or reciprocals of the ultrasonic waves propagating in the flow path in both the forward and reverse directions, a storage means storing the relationship between the respective propagation times or the sum of their reciprocals in the forward and reverse directions of the ultrasonic waves and the temperature of the gas in the measurement state; temperature conversion calculation means for calculating a coefficient based on a ratio between the temperature of the gas output from the storage means and a predetermined reference temperature on the flow rate measurement value measured by the above, and converting it into a flow rate measurement value at the reference temperature; An ultrasonic gas flowmeter characterized by comprising: