SU974135A1 - Resonance level indicator - Google Patents

Description

The invention relates to instrumentation, namely, devices for controlling the level of liquid and bulk media, and can be used in the chemical, petroleum and other industries.

A level control device is known that contains a sensor in the form of a long line segment included in an oscillating circuit in which the inductive or capacitance of the sensor immersed in the medium being measured changes with the level and the resonant frequency of the circuit changes accordingly. Transformation of signals from the sensor is performed by fixing the extremum of the amplitude-frequency characteristic of the sensor using the mode of forced oscillations 11.

The disadvantage of this gauge is its limited ability to improve measurement accuracy due to the non-linearity and instability of the modulator and the variable oscillator.

A resonant level sensor is known, which contains a level sensor with an amplitude detector, connected to the output of the excitation generator and

Cut the peak detector, differential amplifier, trigger and modulator to the input of the excitation generator. . The measurement of the level of the controlled medium I is reduced to the measurement of the frequency of the H2 HF generator.

A disadvantage of this device is the need to convert the output frequency signal into a normalized output signal to control the display devices, which leads to additional error and reduced accuracy.

The purpose of the invention is to increase the volume

15 measurements.

The goal is achieved by the fact that in a resonant level gauge the excitation generator is made in the form of a digital frequency synthesizer,

20 modulator - in the form of a first reversible counter, a reference frequency generator and two coincidence circuits; a frequency divider, a switch, a second reversible counter, a second trigger and a Kipp relay are entered into the device, with the outputs of the first trigger connected to the second inputs of the first and second coincidence circuits, the first inputs of which are connected to the output of the 30 / nor the first reversible counter and through the switch to the input of the second reversible counter, the output of the second coincidence circuit is connected to the subtraction input of the first reversible counter IK and through the divider are pure to the subtraction input of the second reversible counter, the output of which is connected via the second trigger to the input of the kip-relay and the control input of the switch, while the output of the relay is connected to the control input of the first and second coincidence circuits. When using a digital synthesizer frequency tuned by a counter as a trigger generator, the output signal to the measurement result indication is taken from the counter stages, each pump: which corresponds to a certain fixed value of the output frequency of the Synthesizer. Thus, frequency conversion - output signal is eliminated and accuracy is improved. In discrete tuning, the often resonant frequency of the sensor is determined by means of an additional reversible counter with a frequency divider by two on one of the inputs, as the middle of the gap between the trigger thresholds of the signal-relay on either side of the maximum amplitude-frequency characteristic of the sensor. To do this, first, the input of the divider frequency from the resonant frequency of the sensor is determined from the divider input, which is related to the signal-relay threshold by calculating one-half of the number of tuning steps between the alarm threshold thresholds on the divider input, and then, when tuning the frequency from the trigger threshold of the signal relay to the resonant frequency of the sensor, the previously recorded pulses are read from the additional counter until the counter rotates to its initial state. This moment corresponds to the coincidence of the frequency of the synthesizer with the resonant frequency of the sensor. Thus, the error in determining the resonant frequency of the sensor associated with the trigger threshold of the signal relay, as well as the instability of the trigger threshold, is excluded, as the change in threshold does not affect the average value. I FIG. 1 shows a structural diagram of a resonant level gauge; FIG. 2 - graphical characteristics of his work. The resonant level gauge contains a digital frequency switch 1, the signal from which is fed to a resonant level sensor 2 with an amplitude detector, a peak detector 3 connected to the input of a signal relay 4, consisting of differential amplifier 5 and trigger 6, tuning unit 7 containing a clock generator 8 and two circuits And 9 and 10, connected between the outputs of the signal-relay 4 and the inputs of the reversible counter 11 outputs of the stages of which are connected to the inputs of the steps of the frequency control of the digital frequency synthesizer 1 additional reversing midrange tick 12 connected via switch 13 through one input and a frequency divider for two 14 through another input to the outputs of tuning node 7, trigger 15. kip-relay 16 connected in series between the outputs of the additional reversing counter 12 and the control inputs of tuning node 7, with the output trigger 15 pod-. It is also connected to the control input of the switch 13. The resonant level. The numbers work as follows. At the beginning of the measurement cycle, the additional reversible counter 12 is in the initial, zero state. The output signal from the trigger 15 blocks the switch 13, and the pulses from the tuning unit 7 are fed to the input + addition of the reversible counter 11. With each input pulse input to the addition of the reversible counter 11, the frequency at the output of the digital frequency synthesizer 1 is increased by a certain value FJ, (Fig. 2c), corresponding to the adjustment step. FIG. 2a shows tuning pulses arriving at the input of the reversing addition. counter 11, and in FIG. Figure 2b shows the change in frequency at the output of the digital synthesizer when switching the reversing counter 11. The resonant level sensor 2 is excited by the voltage from the digital frequency synthesizer 1. As the frequency of the digital synthesizer 1 approaches the frequency band of the resonant sensor, the level 2 of the output voltage of the sensor increases. FIG. 2 g is the level sensor voltage envelope selected by the amplitude detector, and FIG. 2d is the voltage at the input of the peak detector 3. Until the time t, the voltage at the output of the peak detector 3 repeats the shape of the voltage at the output of the amplitude detector. At the time point C, the voltage amplitude at the output of the amplitude detector of the level sensor reaches a maximum, which corresponds to the coincidence of the output frequency of the digital synthesizer with the resonant frequency of the level sensor. With a further increase in the output frequency of the digital synthesizer 1, the voltage at the output of the amplitude detector of the level sensor decreases, and at the output of the peak detector 3 the maximum value recorded at time t remains. When the frequency deviation of digital synthesizer 1 increases from the resonant frequency of level 2 sensor, the voltage unbalance at the outputs of the amplitude and peak detectors increases and when a certain threshold value is reached, time tj triggers the trigger of signal-relay 4 consisting of differential amplifier 5 and trigger b. The trigger B cjirHyMrelay overturns and the output of a signal from it to the circuits 9 and 10 of tuning unit 7 causes a reversal of the tuning direction. In addition, at the time of the signal-signal relay, the voltage in the peak detector I is reset to the level in the amplitude detector of the resonant sensor. level After the reverse, the tuning pulses go to the subtraction bus of the reversible counter 11 and the frequency divider by two 14 to the subtraction bus of the additional reversible counter 12. In FIG. 2b, the input pulses are fed to the subtraction bus of the reversing counter 11, and FIG. 2e pulses coming through the frequency divider to two at the input of the additional reversing counter 12. With the first impulse received on the subtraction bus of the additional reversing counter 12, a trigger 15 is triggered connected to the output of this counter, after which the lock is released from switch G 2c shows a plot of the output voltage of the trigger 15. As the tuning pulses go on the subtraction bus of counter 11, the frequency at the output of the digital synthesizer decreases and again approaches the resonant frequency of the resonant level sensor. After passing through the resonant frequency of the level sensor 2, the voltage imbalance at the outputs of the amplitude and peak detectors again arises and when the voltage imbalance reaches a threshold value at time -tj, the signal sumer reverses, producing a reversal of the tuning direction. By the time tj, half the number of tuning steps is recorded on the additional reversing counter 12. The frequency of the digital synthesizer 1 is from 2 to between the thresholds of the signal relay on both sides of the maximum, which corresponds to the deviation of the frequency of the digital synthesizer from the resonant frequency of the level sensor. Signal Relay. After the second reverse, the tuning pulses arrive at the addition input of the reversible counter 11 (Fig. 2a) and through the open switch 13 to the input of the additional reversible counter 12, reading the previously registered pulses. FIG. 2g, the pulses are added to the addition to the input of the addition of an additional reversible counter 12. Since the frequency of the pulses is twice as high, then to the middle of the range between the response thresholds of the signal-relay 4, the pulses recorded earlier at the input with a frequency divider by two are read . When the return reversing counter 12 returns to its initial state (time i), the trigger 15 overturns the voltage drop from which the switch-relay 16 turns on. Figure 2i shows the output voltage diagram from the key. By means of a KIPP-relay signal, 16, the tuning unit 7 is blocked, on this the measurement cycle ends | s. At this time, the number of frequency steps of the digital synthesizer from the value of the resonant frequency of the sensor at the zero level to the value of the resonant frequency of the sensor, determined by the measured level, is recorded on the reversible counter 11. The measurement result is read out in digital form as a percentage of the measured level directly from the outputs of the steps of the reversible counter 11. The resolution of the resonant level gauge is determined by the number of fixed frequencies in the frequency tuning range of the digital synthesizer corresponding to the range of the resonant frequency of the level sensor, and in the absence of a measured medium the readout is reversible the counter is zero, and when the sensor is full, the maximum number of fixed parts is recorded on it m range perestroyki.Novy measuring cycle starts on the falling edge of the signal from Kipp-switch. In this case, the lock is removed from the tuning unit and the pulses are again fed to the input of the counter 11. The measurement process is cyclic and each measurement cycle ends with the output of the final result, therefore, the proposed measuring device can be used in multichannel systems. In this case, the sensors are connected to the measuring device alternately by means of a switch and this. By the same switch, the inputs of the memory cells connected with the outputs of the steps of the revision counter are connected. In the memory cells, the measurement result is recorded by.

each channel for the period between measurements about

The resonant level gauge according to the proposed scheme has a high stability, since the frequency grid at the output of the digital synthesizer is stabilized with quartz, and the output frequency value is strictly related to the state of the reversible counter, with the output of the steps of which the output signal of the measured parameter is taken. The instability of the trigger threshold of the signal-relay does not affect the measurement result, since the resonant frequency of the sensor is determined in the middle of the range of the trigger of the signal-relay on both sides of the maximum, thus, the measurement of the threshold does not affect the average value.

The measurement result is expressed in digital form with a direct reading of the measured parameter in percent of the measured level.

The device is implemented on digital integrated circuits, as a result of which it has high reliability.

The proposed resonant level meter allows for improved measurement accuracy.

Claims (2)

1.Viktorov V.A. Resonant level measurement method. M., Energie, 1969, p. 150 2. USSR author's certificate number 485321, cl. G 01 F 23/28, 1973 (prototype). Q ||||| IHIIHItllHIIHII | lll | HI JIIL i Phi1.2