JPS6148843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flow meter using a PLL method, and after a state in which normal sound waves cannot be received (hereinafter referred to as reception abnormality) continues for a long time, a state in which normal sound waves are received is restored. This invention relates to an automatic restart circuit for restarting stable measurements when the system returns to normal.

Figure 1 shows the operating principle of an ultrasonic flowmeter using the PLL method.

The transmission signal output from the transmission circuit 12 is converted into an ultrasonic signal by one of the transceivers 2, passes through the fluid in the pipe 1, reaches the other transceiver 2, and is sent as a reception signal to the reception circuit 3 after passing through the switch SW2. to go into.

The receiving circuit 3 amplifies the received signal and outputs a detection signal to the ΔT/V conversion circuit 5 when the received signal reaches a preset signal detection level. On the other hand, the counting circuit 4 counts the pulse signals from the voltage controlled oscillator (hereinafter abbreviated as VCO) 8 in synchronization with the transmission signal from the transmitting circuit 12, and when the counting circuit 4 finishes counting, it outputs a counting end signal as ΔT/V It is output to the other input of the conversion circuit 5. The ΔT/V conversion circuit 5 calculates a voltage signal proportional to the time difference between the two, passes through SW3, integrates it with an integrator 6, and then outputs it to VCO8.
A pulse signal having a frequency proportional to the voltage is generated and sent to the counting circuit 4 and the transmitting circuit 12.

Now suppose that the timing of the detection signal from the receiving circuit 3 is later than the counting end signal from the counting circuit 4, the ΔT/V conversion circuit 5 and the integrating circuit 6 lower the output pulse frequency of the VCO 8. Assuming that the VCO operates as shown in FIG. By repeating such operations, the system is finally balanced when the input timings of the two input signals of the ΔT/V conversion circuit coincide. The above is SW
Although the case where each switch of SW1 to SW4 is in the illustrated position (downstream side → upstream side transmission) has been described, the same applies to the reverse case. The output (Δ) of the frequency difference conversion circuit in this case is given by the following equation.

Δ=Nsin2θ/D(1+τCcosθ/D) ^-2
・v……(1) N: Amplification factor of Δ (equivalent to the count value of the counting circuit) θ: Incidence angle of ultrasonic wave in water D: Inner diameter of pipe τ: Propagation time other than underwater propagation time of ultrasonic wave C: Underwater Sound velocity v: Flow velocity As can be seen from equation (1), Δ is proportional to the flow velocity v.

Therefore, by extracting a signal proportional to Δ, the flow velocity v can be obtained. This is the operating principle of an ultrasonic flowmeter using the PLL method.

Now, let's consider a case where the transmission and reception of sound waves is interrupted in such an ultrasonic flowmeter. For example, this may occur if air bubbles get mixed in, if solid objects get mixed in, or if the detector is exposed to the air due to lack of water.

In such a case, the reception signal does not reach the reception circuit 3, and therefore the detection signal cannot be output to the ΔT/V conversion circuit. Therefore, a reception abnormality signal is output and the output of the integrating circuit 6 is held.
Keep the oscillation frequency constant in VCO8. Then, when the fluid conditions become normal and the reception signal starts to arrive, the hold of the integrating circuit 6 is released and the VCO is turned on again.
8 control. In this way, even if the measurement conditions are disturbed, the output will not become unstable.

FIG. 2 shows a specific example of an integrating circuit having the above-mentioned hold function.

The ΔT/V conversion signal 13 is integrated with a time constant determined by the resistor _R1 and the capacitor 16, and then the reference power supply 1
By adding a bias of 7, it becomes the input voltage of VCO8.

The electronic switch 14 is normally turned on, but when the reception abnormality signal 19 is received, it is turned off, stopping the integral operation and holding the output. The reference power supply 17 is for applying DC bias to the input of the VCO 8, and the output voltage of the integrating circuit becomes zero at startup, but even in that case, the output voltage of the VCO 18
Set the operating point so that the output occurs and the PLL loop starts.

However, such conventional circuits have the following drawbacks. It has already been mentioned that in ultrasonic flowmeters, the transmission and reception of sound waves may be hindered depending on the measurement conditions, but this condition may continue for a long time, for several hours or more, and in some cases for several days or more. For example, this applies to measuring the flow rate when water is pumped from below to a water source pond located on a hill. In this case, the pump often operates intermittently, and the pump may be inactive for several hours or more. In that case, it will stop once, but it will gradually lower due to its own weight, and eventually there will be no water in the ultrasonic propagation path at the detector mounting part, and normal transmission and reception of sound waves will not be possible. If the transmission and reception of sound waves is prevented for a long period of time in this way, the integrating circuit shown in FIG. As a result of the change in the output of 15, the operating point of the VCO shifts and even if it becomes normal, it cannot be restarted. This is because in order to prevent malfunctions due to noise, ultrasonic flowmeters generally set a reception gate and perform signal processing in which only signals between those gates are considered as received signals.In the PLL method, the VCO output Create a reception gate like this from Accordingly
This is because there is a certain tolerance range for the VCO output in order for the PLL loop to start, but as a result of drift, it falls outside of that range. Conventionally, in such a case, it was necessary to turn off the power and then turn it on again.

As mentioned above, the present invention has a restart function that automatically restarts measurement as soon as the system returns to normal even if the transmission and reception of ultrasound is interrupted for a long period of time, without having to manually turn the power back on as in the past. Our goal is to provide the following.

An example is shown in FIG. The counting circuit 20 is always reset during normal operation, and counts the pulse signal input 21 only when reception becomes abnormal, and when counting is completed, the electronic switch 22 is turned "ON".

As a result, the capacitor 16 is short-circuited and discharged, and is reset to the same state as when the power was turned on.

If the counting time of the counting circuit 20 is selected to a value during which the amount of drift in the integrating circuit can be ignored, even if the reception abnormality continues for a long period of time, the integrating circuit will be reset at regular intervals determined by the counting time, and the drift will be eliminated. Corrected. Then, at the same time as the measurement state returns to normal, the counting circuit 20 enters the reset state, the electronic switch 22 is turned off, and the integrating circuit performs the normal integrating operation. In other words, it resumes operation as a flowmeter.

A time chart of these operations is shown in FIG.

Note that Δ will also change when the reset operation is repeated due to an abnormal reception, but a hold circuit is provided at the output stage that converts the Δ signal into an analog signal proportional to the flow rate, and the previous value is held when there is an abnormal reception. Alternatively, if the flow rate is forcibly reduced to zero, the fluctuation in Δ caused by the above reset operation will not appear in the output. Further, a pulse generation circuit that generates pulses of a constant frequency may be provided separately for the pulse signal input 21, or the output signal of the VCO 8 may be used.

In the above explanation, the case of an ultrasonic full-water flow meter has been described, but it is also possible to apply the present invention to a flow velocity measuring section of an open channel flow meter. Particularly in open channel flowmeters, it is common for the water level to fall below the flow rate detector, and applying the function of the present invention is effective because it can automatically switch from low water level to high water level. .

As described above, according to the present invention, it is no longer necessary to manually restart the operation after a long period of abnormal reception, and as a result, automatic measurement in special pipes, which was practically difficult to apply in the past, is now possible. It is now possible, and the effects are great.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams for explaining the prior art, and FIG. 3 is a diagram showing a specific embodiment of the present invention.
FIG. 4 is a diagram for explaining the content of the present invention. 1... Piping, 2... Transmitting/receiving element, 3... Receiving circuit, 4, 20... Counting circuit, 5... ΔT/V conversion circuit, 6, 7... Integrating circuit, 8, 9... Voltage controlled oscillator , 10... Frequency difference conversion circuit, 12... Transmission circuit, 14, 22... Electronic switch, 15...
Operational amplifier, 16... capacitor, 17... reference power supply.

Claims (1)

[Claims] 1 A pair of transceivers installed in the piping and transmitting and receiving ultrasonic waves propagating through the fluid to be measured in the piping;
a converting circuit that obtains a voltage proportional to the time difference between the received signal received by the transceiver and the output signal of the first counting circuit; and an integrating circuit that integrates the output voltage from the converting circuit. a voltage controlled oscillator that outputs a pulse signal of a frequency corresponding to the output of the integrating circuit and the reference voltage to the first counting circuit; means for blocking input; a second counting circuit for counting pulse signals according to the abnormal signal; and means for resetting the integrating circuit each time the second counting circuit reaches a predetermined counting time. An ultrasonic flow meter characterized by the following configuration.