JPH10142019A5 - - Google Patents

Description

[0023]
[Means for solving the problem and their effects]
In order to achieve the above object, the invention of claim 1 comprises:
An ultrasonic flowmeter is provided with at least one pair of ultrasonic transmitters and receivers (1) and (2) that function both as a transmitter and a receiver, and transmits and receives ultrasonic waves from upstream to downstream and from downstream to upstream in a fluid flow, and determines the flow velocity and flow rate from the arrival time of the ultrasonic waves in each direction,
First, the transmitting transducer (1) emits a signal, and when the receiving wave detector (4) that inputs the signal from the receiving transducer (2) detects the received wave, the transmitting transducer (1) emits a signal again. This is configured to be repeated a certain number of times (n times), and the time from the first transmission to the certain number of times (nth reception) is measured , and the flow velocity and flow rate are calculated from the result.
The received wave detection unit (4) is composed of an amplifier unit and a comparator unit, and the signal from the transmitting transducer (1 or 2) is first amplified and then compared with a reference voltage level, and the point at which the wave that first exceeds the reference voltage level then passes through the zero level is considered to be the point at which the received wave is detected,
The reference voltage level can be changed in several steps, and apart from the normal measurement for determining the flow velocity, the reference voltage level is changed stepwise periodically or irregularly in the forward direction and the reverse direction, for each transmission and reception or for each of several transmissions and receptions, and ultrasonic waves are transmitted and received multiple times in succession in the same manner as in the normal measurement.
This ultrasonic flowmeter is characterized by being able to monitor changes in the arrival time of each transmission and reception, and when it is determined that the change in the arrival time is large for one step change for some reference voltage levels, optimal reference voltage levels are determined for the forward direction and the reverse direction from those reference voltage levels, and those levels are used for normal measurements.

[0024]
The arrival time of the ultrasonic waves in each direction may be measured by collectively measuring the time from the first transmission to the reception of a certain number of times (nth time), that is, n times the arrival time.
If the times from the transmission pulse corresponding to the transmission drive signal for each transmission and reception to the detection of the zero crossing point of the received wave are, for example, t1, t2, ... for n consecutive transmissions and receptions, then the total time required for n consecutive transmissions and receptions is approximately nt + nτ, and the change in flow velocity during this time can be considered to be almost zero. Therefore, as long as the reference voltage level serving as the threshold value reliably captures the specific target wave, t1, t2, ... will be almost the same value, and the difference between two adjacent values will be almost zero.

[0036]
The ratio of the third wave to the first wave cannot be detected unless the peak of the first wave is equal to or greater than V _TH1 and the peak of the third wave is smaller than the maximum reference voltage level provided, that is, V _TH24 in FIG.
The invention of claim 3 is an ultrasonic flowmeter according to claim 1, characterized in that when the reference voltage levels when the change in the arrival time of each transmission and reception was greatest are arranged from smallest to largest, a reference voltage level that is equal to or greater than a certain multiple of the next smaller reference voltage level is detected, and the reference voltage level intermediate between that reference voltage level and the previous reference voltage level is determined as the optimum reference voltage level.

[0037]
The invention of claim 4 is the ultrasonic flowmeter of claim 2 or 3 ,
The amplification factor of the amplifier of the received wave detection unit is configured to be changeable in several stages, and if there is no reference voltage level that is a fixed multiple of the next smaller reference voltage level, the amplification factor is changed in sequence and transmission and reception to determine the reference voltage level is carried out for each amplification factor, and if there is a reference voltage level that satisfies the above condition, that amplification factor is determined to be the optimum amplification factor and is used for normal measurements.

[0039]
The invention of claim 5 is the ultrasonic flowmeter of claim 2, 3 or 4 ,
The reference voltage level is provided in a plurality of stages in an exponential manner of voltage.

[0040]
In the inventions of claims 2, 3, and 4 , whether the third wave/first wave etc. is above a certain value is determined by first calculating the ratio and then comparing it with a certain value. However, division using a microcomputer or the like is cumbersome. Therefore, the invention of claim 5 makes it possible to determine whether the above conditions are met without performing the cumbersome division operation.

[0058]
10 shows a specific example of the electrical circuit of the comparison section of the received wave detection section 4 in the above embodiment, in which the output V _OUT from the amplifier section of Fig. 9 is input to the non-inverting input of the comparator 16. The reference voltage level V _TH is input to the inverting input.

[0059]
S20, S21, and S22 are reference voltage level selection signals from the control unit 8. By selecting and turning on one of the analog switches 17, a constant reference voltage 18 is divided by one of the eight resistors R40 to R47 and the resistor R3 to generate the reference voltage level _VTH to be input to the inverting input of the comparator 16.

[0060]
The relationship between the resistance values of the eight resistors R40 to R47 is as follows:
R40<R41<R42<...<R47
The analog switch 17 is selected by a reference voltage level selection signal from the control unit, and the reference voltage level can be selected.

Claims (5)

An ultrasonic flowmeter is provided with at least one pair of ultrasonic transmitters and receivers that function both on the transmitting side and on the receiving side, and transmits and receives ultrasonic waves from upstream to downstream and from downstream to upstream in the flow of a fluid, and determines the flow velocity and flow rate from the arrival time of the ultrasonic waves in each direction,
First, the transmitting transducer emits a signal, and when the receiving wave detector that inputs the signal from the receiving transducer detects the received wave, the transmitting transducer emits a signal again. This is repeated a certain number of times (n times), and the time from the first transmission to the certain number of receptions (nth time) is measured , and the flow velocity and flow rate are calculated from the results.
The received wave detection unit is composed of an amplifier unit and a comparator unit, and the signal from the transmitting transducer is first amplified and then compared with a reference voltage level, and the point at which the wave that first exceeds the reference voltage level then passes through zero level is regarded as the point at which the received wave is detected,
The reference voltage level can be changed in several steps, and apart from the normal measurement for determining the flow velocity, the reference voltage level is changed stepwise periodically or irregularly in the forward direction and the reverse direction, for each transmission and reception or for each of several transmissions and receptions, and ultrasonic waves are transmitted and received multiple times in succession in the same manner as in the normal measurement.
This ultrasonic flowmeter is characterized in that it is possible to monitor changes in the arrival time of each transmission and reception, and when it is determined that the change in the arrival time is large for one step change for some reference voltage levels, it determines the optimum reference voltage levels for the forward direction and the reverse direction from those reference voltage levels, and uses those levels for normal measurement. 2. The ultrasonic flowmeter according to claim 1, wherein when the reference voltage levels when the change in the arrival time of each transmission and reception is large are arranged from smallest to largest, a reference voltage level that is equal to or greater than a certain multiple of the next smaller reference voltage level is detected, and an approximate average value of that reference voltage level and the next smaller reference voltage level is determined as the optimum reference voltage level. 2. The ultrasonic flowmeter according to claim 1, wherein when the reference voltage levels when the change in the arrival time of each transmission and reception was greatest are arranged from smallest to largest, a reference voltage level that is equal to or greater than a certain multiple of the next smaller reference voltage level is detected, and a reference voltage level intermediate between that reference voltage level and the previous reference voltage level is determined as the optimum reference voltage level. 4. The ultrasonic flowmeter according to claim 2, wherein the amplification factor of the amplifier of the received wave detection unit can be changed in several stages, and when there is no reference voltage level that is a fixed multiple of the next smaller reference voltage level, the amplification factor is changed in sequence and transmission and reception to determine the reference voltage level is performed for each amplification factor, and when there is a reference voltage level that satisfies the condition, that amplification factor is determined to be the optimum amplification factor and is used for normal measurement. 5. The ultrasonic flowmeter according to claim 2, wherein the reference voltage level is provided in a plurality of stages in an exponential function of voltage.