JPS5856415B2 - Phase demodulation circuit for ultrasonic detection type vortex flowmeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phase demodulation circuit in an ultrasonic detection type vortex flow meter.

A conventional phase demodulation circuit for a vortex flowmeter will be explained with reference to FIG.

In the figure, 1 is a flowmeter having a vortex generator 2, 3 is a generated Karman vortex, 4 is an ultrasonic transmitter, 5 is an ultrasonic receiver, 6 is an induced sound oscillation circuit, and I is a voltage-controlled phase shift circuit. , 8
9 is a waveform shaping circuit, 9 is a phase comparator, 10 is a loop filter, and 11 is a low-pass filter.

In the phase demodulation circuit configured as described above, the ultrasonic wave emitted from the ultrasonic oscillator 4 is phase-modulated by the Karman vortex street of the Karman vortex 3 and is received by the ultrasonic receiver 5.

The received wave is waveform-shaped by a waveform shaping circuit 8.

The phase comparator 9, the ultrasonic oscillation circuit 6, the voltage-controlled phase shift circuit 7, and the loop filter 10 constitute a phase-locked loop.

Further, the voltage-controlled phase shift circuit 7 controls only the phase shift angle while maintaining the high frequency stability of the ultrasonic oscillation frequency signal.

It is assumed that the characteristics of the loop filter 10 in the phase-locked loop configured as described above are set so as to be able to follow the modulation angular frequency of the phase modulated signal by the vortex 3 at a sufficiently high speed.

In this case, the output of the loop filter 10 (hereinafter referred to as output 1) changes so as to synchronize the output of the voltage controlled phase shift circuit 7 with the ultrasonic reception signal.

In other words, output 1 becomes the phase demodulation output as it is.

The phase synchronization angle of the phase open loop is determined by the characteristics of the phase comparator 9 and the loop filter 10.

When using the phase comparator 9, which has been integrated into an IC in recent years, O2π/2
．． A phase synchronization angle such as π can be easily realized.

However, in the phase demodulation circuit configured as described above, if the speed of sound changes due to a change in the temperature of the fluid, the received ultrasonic wave will undergo a large phase shift, and the voltage-controlled phase shift The phase shift amount of the circuit 7 is required to have a wide angle phase shift far exceeding 2π, which has the disadvantage of complicating the circuit.

Furthermore, if the loop filter 10 is then set to a large time constant so that it cannot follow the modulation angular frequency of the phase modulation signal due to thinning, the output signal of the voltage controlled phase shift circuit 7 , the average phase and average frequency of the ultrasonic multiplied signal can be determined, and a signal with high frequency stability can be obtained.

FIG. 2 shows an example of the phase comparator 901 used in FIG. 1, and is composed of an exclusive OR circuit 9.

Here, the low-pass filter 11 for the carrier filter
FIG. 3 shows the demodulated output characteristics with respect to the phase difference of the input.

If the above exclusive OR circuit 91 is used and the loop filter 10 is set to form a phase-locked loop so that the average phase difference is equal to or smaller than the average phase difference, a phase demodulated output can be obtained at output 2, and a minute phase deviation can be obtained. Great demodulation sensitivity can be obtained even with respect to shifts.

However, in this case, the phase shift angle of the voltage controlled phase shift circuit 7 described above is changed to a phase locked loop so that only the portion corresponding to the average phase shift between the ultrasonic transmitter and the receiver is compensated. , the demodulation of phase modulation with a high modulation angular frequency has the drawback that only phase modulation from O to π radians can be demodulated with good linearity due to the characteristics of the exclusive OR circuit 91. there were.

Furthermore, FIG. 4 shows another example of the phase comparator 9 described above.
is an edge-triggered set-reset clip-flop circuit.

Here, the demodulated output characteristics with respect to the phase difference of the input in the low-pass filter 11 are shown in FIG.

By setting the loop filter 10 using the set-reset flip-flop circuit 92 described above, the average phase difference is set to π.
Even if a phase-locked loop is configured so that

In other words, the output of the set-reset flip-flop circuit 92 is a periodic function with a phase difference of 2π.

For this reason, in cases such as ultrasonic detection type vortex flow meters, wide angle phase modulation exceeding 2π may occur depending on the selection of the ultrasonic oscillation frequency and the facing distance between the ultrasonic transmitter and receiver. However, it is difficult to demodulate the phase beyond this range, and the circuit is complicated.

The present invention aims to eliminate the above-mentioned drawbacks, and provides a phase demodulation circuit for an ultrasonic detection type vortex flowmeter that reduces the phase shift angle of a voltage-controlled phase shift circuit and enables wide-angle phase demodulation. It is something to do.

An embodiment of the present invention will be described below with reference to FIG.

In the figure, 12 and 13 are the first . The frequency division ratio of the second frequency divider is N.

Note that the phase-locked loop is constituted by a frequency-divided frequency signal.

Furthermore, explanations of other symbols are omitted as they are the same as those of the prior art.

In the configuration as described above, the ultrasonic oscillation frequency signal is frequency-divided by the second divider 13 and inputted to the voltage controlled phase shift circuit 7, and the ultrasonic reception signal is input to the first divider 12. The frequency is divided by and input to the phase comparator 9.

Here, a case will be described in which a high-speed phase-locked loop is constructed, as described in the case of extracting the phase demodulated output from output 1 in FIG. 1 of the conventional circuit.

In this case, the voltage-controlled phase-shift circuit 7 has a 1/N divider number of the ultrasonic oscillation frequency, so the phase shift angle in the voltage-controlled phase-shift circuit 7 is 1/N. Reduced.

Next, a case will be described in which a phase-locked loop with a large time constant is constructed, as described in the case of extracting the phase demodulated output from the output 2 in FIG. 1 of the conventional circuit.

In this case, the frequency signal whose frequency has been divided by N is input to the phase comparator 9 .

Since the phase difference between the 1/N frequency divided waves is N times larger when converted to the phase difference at the fundamental frequency, the phase range in which the phase is demodulated with good linearity is expanded by N times.

In the above embodiment, the present invention is applied to a phase demodulation circuit of an ultrasonic detection type vortex flowmeter, but it goes without saying that the present invention can also be used for demodulation of other phase modulation measurement devices using ultrasonic waves. .

As described above, the present invention can realize a wide-angle phase demodulation circuit with a simple configuration of configuring a phase-locked loop including a divider and a voltage-controlled phase shift circuit. This has the effect of reducing the amount of phase shift.

[Brief explanation of the drawing]

Figure 1 is a demodulation circuit diagram of a conventional vortex flowmeter, Figure 2 is a circuit diagram showing an example of the phase comparator shown in Figure 1, and Figure 3 is a case where the phase comparator shown in Figure 2 is used. FIG. 4 is a circuit diagram showing another example of the phase comparator shown in FIG. 1, and FIG. FIG. 6, which is a human output characteristic diagram of the filter 11, is a circuit diagram showing an embodiment of the present invention. In the figure, 6 is an ultrasonic oscillation circuit, 7 is a voltage controlled phase shift circuit, 9 is a phase comparator, 10 is a loop filter, 11
is a low-pass filter, 12 is a tenth frequency divider, and 13 is a second frequency divider.
is a frequency divider. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A vortex generator disposed in a fluid, an ultrasonic transmitter provided to propagate ultrasonic waves across the flow of the Karman vortex street generated on the downstream side of the vortex generator, and this ultrasonic transmitter. an ultrasonic oscillation circuit that excites the ultrasonic wave, an ultrasonic receiver that receives the ultrasonic wave phase-modulated by the Karman vortex, a tenth frequency divider for dividing the frequency of the received signal of this ultrasonic receiver, and this tenth frequency divider. a phase comparator that uses a signal from a frequency converter as one input; a loop filter that removes unnecessary frequency components from the output of the phase comparator; a second frequency divider that divides the output signal of the oscillation circuit; The phase deviation angle from the output signal of this 20th frequency divider generates an output signal controlled in accordance with the output voltage of the loop filter, and this output is a voltage that becomes the other input of the phase comparator. A phase demodulation circuit for an ultrasonic detection type vortex flow meter characterized by being equipped with a controlled phase shift circuit.