JPS5855441B2 - How long can you use it? - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for providing a time reference signal.

In particular, the present invention relates to an apparatus for providing a time reference signal from pulses of high frequency electrical signal oscillations, such as those used for example in fluid flow rate measurements using ultrasonic pulses.

There are several ways in which the time of occurrence of such a pulse can be electronically marked.

One method is to detect the arrival of a pulse by a threshold detector, and use the trigger time of the threshold detector as a time reference.

Another method is to detect when the pulse reaches its maximum value.

These methods provide significantly better timing precision than the pulse gold standard (typically 0.1 microsecond duration).

However, if the amplitude of the pulse fluctuates, the quarter wavelength
That is, for a 10MHz signal, it is approximately 0.025
This can cause timing fluctuations of as much as microseconds.

Although this was thought to be accurate enough in most cases, the inventors decided to make further improvements to this system to provide timing accuracy of +1 second. .

According to the invention, in a measurement method using pulses consisting of short bursts of high frequency oscillations, the timing accuracy is increased by applying zero value crossing detection to the high frequency signal.

To avoid errors resulting from zero-value cross measurements for abnormal signal oscillations, the integral value of the signal amplitude is checked by comparing it to a specific reference value.

That is, according to the present invention, there is provided a device for providing a time reference signal from a pulse of an electric signal vibration, the device for receiving the pulse and detecting that the amplitude of the pulse exceeds a predetermined threshold level. a detection device; a zero-crossing detector coupled to the detection device to provide a signal output at the moment when the electrical signal oscillation passes through a zero value after said detection by the detection device; an integral amplifier for providing an output indicative of the integral of the amplitude of the vibration signal over the entire duration of the vibration signal; a value such that when a valid indication is given, and when the vibration signal is such as to cause the zero value crossing detector to operate in a cycle different from the predetermined cycle of the vibration signal, an invalid indication is given; The output of the integral amplifier is compared with a predetermined reference value set to a predetermined reference value, and when the output exceeds the predetermined reference value, it is determined that the signal output of the zero value crossing detector is valid. and means for instructing that the signal output of the zero value crossing detector is invalid when the output thereof is less than the predetermined reference value. be done.

According to the time reference signal supply device of the present invention, in the case of a vibration signal in which zero value crossing detection is performed outside of a predetermined cycle of the vibration signal, the given time reference signal may be invalid. The time reference signal that is designated and designated as valid is always obtained by detecting zero value crossings at predetermined cycles of the vibration signal, so it is highly accurate (and the time reference signal is error-free). .

Next, the present invention will be described in more detail with reference to embodiments of the present invention based on the accompanying drawings.

The present invention can be applied to, for example, a flow rate measuring device as disclosed in Japanese Patent Application Laid-Open No. 49-48351.

This device operates on the principle of simultaneously initiating the transmission of ultrasound pulses through a fluid and the counting of pulses or oscillations from a voltage-controlled oscillator.

The time of arrival of the received pulse or ultrasound wave is compared to the time of arrival of the Nth pulse or vibration from the voltage controlled oscillator and voltage controlled to match the time of arrival of each of these. An adjustment is made to the frequency of the oscillator's vibrations.

In this way, by matching a predetermined number (N) of pulses or oscillations during the flight of the ultrasound pulse through the fluid along the same path but in opposite directions, two opposing directions of propagation of the ultrasound pulse can be achieved. From the difference in the frequency of the voltage controlled oscillator corresponding to , it is possible to calculate the components of the fluid flow velocity through the passage '&5.

It will be appreciated that the accuracy of the device depends, inter alia, on the accuracy with which the time reference is determined based on the received ultrasound pulses.

A transducer converts the received ultrasound pulses into electrical signals whose waveforms are shown in FIGS. 1A and 1B.

In the graphs shown in these figures, the horizontal axis represents time and the vertical axis represents the signal amplitude at the output of amplifier 22 (FIG. 2A).

In FIG. 2A, the signal from the transducer is 21
is sent to an amplifier 22, the output of which is applied to a threshold detector 23 and a zero value detector 24.

Its operation is controlled by strobe 25 (5trobe).

The strobe 25 keeps the detection circuit active only for a predetermined period of time that includes the time of arrival of the expected pulse.

The purpose of this strobe is to prevent undesired operation from spurious signals.

FIG. 1A shows a received signal of sufficient amplitude for normal operation.

The dotted line 26 represents the threshold level set by the threshold detector 23.

The structure of this example is such that the zero-crossing detector outputs the next positive-going zero crossing of the received signal after the negative-going excursion of the signal exceeds the threshold level 26 of the threshold detector. is configured to give.

Thus, the output of the zero crossing detector is 27 as shown in FIG. 1A.
corresponds to the position of

It will be appreciated that the amplitude of the received ultrasound pulses is likely to vary, particularly when there are bubbles or solids in the fluid suspension.

JP-A-49-48351 describes how measures were taken to prevent errors in the flow velocity measurements indicated by the device by completely blocking some of the ultrasonic pulses. There is.

However, although this device operates by detecting the received signal, the amplitude of the detected signal may be too low to give erroneous results.

This is illustrated in Figure 1B, where the received signal has been attenuated so much that the first negative-going stroke does not activate the Schles Soshold detector and the second negative-going stroke does not activate the Schles Soshold detector. It can be seen from this figure that the tschhold detector operates.

The zero crossing detector then provides an output at position 28 in FIG. 1B, which position is offset by one cycle of high frequency oscillation from the desired position for the time reference.

Such effects can be reduced by providing automatic gain adjustment for amplifier 22.

This is shown in FIG. 2A, where device 29 is connected to amplifier 22.
detects the amplitude of the output from the circuit and provides a voltage signal representing this amplitude, which is compared by a comparator 31 with a reference voltage VR.

The output of comparator 31 controls the gain of amplifier 22 to attempt to maintain the amplitude of the output signal at a constant level.

However, automatic gain control necessarily operates with a relatively long time constant, adjusting amplifier gain only when the average received signal level changes.

Therefore, if, for example, only a small portion of a significantly attenuated signal is received, it is possible that such an attenuated signal will reach the threshold detector 28 in the form shown in FIG. 1B.

FIG. 2B shows an arrangement for providing an output signal indicating that the amplitude of the received signal applied to the threshold detector 23 is satisfactory.

The output of amplifier 22 on line 32 is the strobe 2
The signal is sent to an integral amplifier 34 via a linear gate 33 controlled by 5.

The output of the integrating amplifier 34 is compared with a reference voltage by a trigger circuit 35.

Trigger circuit 35 is configured to set flip-flop 36 when the output of the integral amplifier exceeds a predetermined level.

The operation of this circuit is as follows.

The linear gate 33 is turned on by the strobe pulse so that the output of the amplifier 22 is connected to the integrating amplifier 34 only during the strobe period, ie, during the period that includes the expected received pulse arrival time.

The input to the integrating amplifier is low impedance (the "summing" point) at the voltage set by variable resistor R2.

Diode D conducts when the signal is negatively larger than this voltage by the magnitude of Vf.

Here, Vf is the voltage required for diode D to conduct.

Resistor R2 is set so that diode D turns on when the signal voltage is slightly more negative than the amplifier output noise.

This prevents this noise from affecting the integrating amplifier.

The time constant of the capacitance and resistance combination CfRf is configured to be much larger than the strobe time and much smaller than the delay time between receptions of successive receive pulses.

In this way, true integration can occur during the strobe time, but there is sufficient time for the voltage across capacitor Cf to decay to a zero value before the next strobe pulse.

The instantaneous current flowing through resistor R1 and diode D into integrating capacitor Cf is given by:

here, vRX - amplitude of the signal, vf = diode forward voltage drop ■R2 - Reference voltage to operational amplifier A The shape of the current I is shown at the bottom of FIG.

The upper part of FIG. 3 shows the waveform of the output of the amplifier 22 for comparison.

The output voltage of the operational amplifier A applied to the trigger circuit 35 is proportional to the total charge integrated into the capacitor Cf during the strobe time, that is, the output voltage is proportional to the total area of the shaded area in FIG. Proportional.

The trip level of trigger circuit 35 is adjusted using variable resistor R3 to ensure that a received signal having an average amplitude sufficient to cause a voltage output from the amplifier greater than the trip level is zero. It should be appropriately thick enough to allow the crossover detector to operate properly.

FIG. 4 shows that the device of FIG. 2B is installed in the flow rate measuring device to inhibit adjustment of the voltage controlled oscillator if the amplitude of the received pulse is too low to operate satisfactorily the zero crossing detection screen. This shows how it is installed.

FIG. 4 shows a portion of the apparatus corresponding to FIG. 3 in the above-mentioned Japanese Patent Application Laid-Open No. 49-48351.

The operation of the circuit of FIG. 4 is as follows.

The starting pulse from the master oscillator resets all three flip-flops 45, 46, 470.

Depending on which pulse arrives first, any received pulse RX from the voltage controlled oscillator can set either flip-flop 45 or flip-flop 46.

Thus, when a received RX pulse arrives first, flip-flop 45 is set and subsequent setting of flip-flop 46 is inhibited.

When the Nth pulse from the voltage controlled oscillator arrives first, flip-flop 46 is initially set, inhibiting subsequent setting of flip-flop 45.

If the received RX pulse arrives first, the adjustment of the voltage controlled oscillation frequency is performed by the increments of the monostable circuit 50 operating the level shift as described in the aforementioned Japanese Patent Publication No. 49-48351. It will be done.

However, the output from set flip-flop 45 is applied to monostable circuit 50 via AND gate 48, which inhibits operation of the monostable circuit until flip-flop 47 is set if it is not set. do.

Similarly, a corresponding reduction in the frequency of the voltage controlled oscillator when the Nth pulse from the voltage controlled oscillator arrives first is effected by the monostable circuit 51 and the associated level shift.

In this case as well, the output from the set flip-flop 46 is sent to the monostable circuit 51 via the AND gate 49, which is connected to the monostable circuit 51 unless the flip-flop 47 is set. The operation of the circuit 51 is prohibited.

Flip-flop 47 corresponds to flip-flop 36 in FIG. 2B, and is controlled by the output of a combination of integral amplifier 34 and trigger circuit 35, indicated by box 54 in FIG. is supplied with the signal output from the amplifier 22 via a linear gate 33 controlled by a strobe.

Thus, if the received signal does not have an amplitude determined by the structure of FIG. 2B to be sufficient for the zero-crossing detector to operate satisfactorily, neither monostable circuit 50 nor monostable circuit 51 Can't work.

In the event of a disturbance in the ultrasound pulse, since there is no received pulse and the flip-flop 47 remains in its reset state, the structure of FIG. 4 naturally does not include means for adjusting in such a case. .

Assuming that a certain minimum portion (for example, 10%) of the received signal is normal, even when a certain portion of the received signal is completely absent, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 4948351, In the same way as above, correct operation can be achieved by storing the control voltage of the voltage controlled oscillator.

The invention is not limited to the examples described above.

The apparatus shown in FIG. 2B is the fourth in the apparatus disclosed in Japanese Patent Application Laid-Open No. 49-48351 for measuring fluid flow velocity.
It is particularly advantageous when used in the manner shown in the figures.

However, the apparatus of FIG. 2B can be used wherever it is desired to establish an accurate time reference for signal pulses of the form shown in FIG.

[Brief explanation of drawings]

Figures 1A and 1B show the waveforms of the signals. Figures 2A and 2B are circuit diagrams of a portion of the device. FIG. 3 shows other waveforms. Figure 4 is Figure 2A and Figure 2.
2 is a block diagram of a portion of the device that includes the device of FIG. 21... Amplifier input, 22... Amplifier, 23.°°... Schreshhold detector, 2
4... Zero value crossing detector, 25... Strobe, 26... Schreshhold level, 27, 28... Zero crossing position, 29... ...
- Width detector, 31... Comparator, 32...
... Line, 33 ... Linear gate, 34 ...
... Integral amplifier, 35 ... Trigger circuit,
36...Flip-flop, R1...
Resistor, R2, R3... Variable resistor, D...
... Diode, A ... Operational amplifier, Cf.
... Capacitor, Rf ... Resistor, 45°46.47 ... Flip-flop, 48,49
...AND gate, 50, 51...monostable circuit.

Claims (1)

[Claims] 1 A device for providing a time reference signal from a pulse of electrical signal vibration, the detection device receiving the pulse and detecting that the amplitude of the pulse exceeds a predetermined threshold level; a zero-crossing detector coupled to said detection device to provide a signal output at the moment when said electrical signal oscillation passes through a zero value after said detection by the device; an integral amplifier providing an output indicative of the integral of the amplitude of the signal; and a valid indication provided when the vibration signal is such as to activate the zero crossing detector at a predetermined cycle of the vibration signal; and a predetermined value set to a value such that an invalid indication is given when the vibration signal is such as to activate the zero value crossing detector in a cycle different from the predetermined cycle of the vibration signal. A reference value is compared with the output of the integral amplifier, and when the output exceeds the predetermined reference value, it is indicated that the signal output of the zero value crossing detector is valid, and the output is A time reference signal supply device comprising: means for instructing that the signal output of the zero value crossing detector is invalid when the signal output is less than the predetermined reference value.