RU2459351C1 - Device for generating pulses from signals of rotational frequency inductive sensors - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: generator includes an input RC-type low-pass filter with cut-off frequency in the lower region of the frequency range of the generator; the input of the filter is connected to the output of the inductive sensor; the output of the filter is connected to the first input of a comparator and the second input of the comparator is connected to a reference signal source through an analogue multiplexer.

EFFECT: high reliability of operation and significant simplification of the circuit of the pulse generator.

2 dwg

Description

The invention relates to measuring equipment and can be used in automatic measurement, control and emergency protection systems, which include sensors that generate bipolar signals, in particular induction sensors of speed and flow.

The features of the operation of sensors of this type when measuring the rotation parameters of real objects are a linear dependence of the amplitude of the output signal of the sensors on the frequency [1] and a significant level of interference in the output signal, which imposes significant restrictions on the circuitry of pulse shapers. So, with a change in the rotor speed from 300 rpm to 30,000 rpm, the amplitude of the output voltage of the induction sensor will also increase 100 times, and with an increase in the rotor speed, the level of interference will significantly increase. The presence of interference in the output signal of the induction sensors depends both on the vibrational state of the measured object, and on the workmanship and design features of the induction sensor itself together with the rotor. At the input of the pulse shaper there are also periodic and single electromagnetic disturbances generated during the operation of various kinds of energy converters, electric machine elements, switches, valves with an electric drive. All of the above interference leads to false positives of the pulse shaper and the shift of the moment of switching the pulse shaper relative to the true position, which causes errors in the measurement of speed.

To reduce the influence of various kinds of interference on the output signal, the circuits of pulse shapers of signals of induction speed sensors are constructed using comparators with hysteresis - Schmitt trigger [2]. In order to significantly reduce the range of variation of the input signal of the comparator, an input integrator is used, which converts the input pulses into "volt-second areas" of the input signals, which are little dependent on the rotor speed. In addition, the integrator filters high-frequency interference, thereby further increasing the noise immunity of the pulse shaper.

A device for generating pulses from signals of induction speed sensors [3], consisting of an input integrator, a comparator, constructed according to the Schmitt trigger scheme, a sampling-storage device for fixing the maximum volt-second area, a control device. Its disadvantage is the sufficient complexity, the inability to change the hysteresis level depending on the parameters of the input signal and the lack of reliability due to the fact that only one signal polarity is used to generate pulses from the signals of the induction speed sensors.

Of the known closest in technical essence is a device that implements a method of generating pulses from signals of induction speed sensors [4]. Its structural diagram is shown in figure 1. The device contains two comparators (3 and 4), an inverter (2), a reference signal source (1), frequency meters (5) and the rate of change of frequency (6), a timer (5). A distinctive feature of this device is the blocking of the switching of the comparators from the moment of the previous switch to the expected time until the next switch. The blocking time of the comparators is set by a timer and is determined by extrapolation based on the results of measuring the frequency and rate of change.

The disadvantage of this pulse shaper is the lack of noise immunity in the event of various kinds of interference acting after removing the blocking of the comparators. The interference acting after removing the blocking of the comparators shifts the moment of switching the pulse shaper relative to the true position, which leads to significant errors in the measurement of frequency and, especially, the speed of frequency measurement. In this case, the prediction of the lock time of the comparators will be made with large errors, which in the next measurement steps will cause even greater errors in the measurement of speed. In addition, the disadvantage of the device can be attributed to its complexity caused by the presence of two comparators, frequency meters and the rate of change of frequency, timer.

The present invention is aimed at improving the reliability of operation and simplifying the shaper circuit.

This goal is achieved by the fact that in the pulse shaper from the signals of induction speed sensors containing a comparator and a reference voltage source, according to the invention, an RC-type low-pass filter is introduced having a cut-off frequency located in the lower region of the frequency range of the shaper, and to the filter input the output of the induction sensor is connected, the output of the filter is connected to the first input of the comparator, and the second input of the comparator is connected to the source of the reference signal via an analog tipleksora.

The low-pass filter introduced into the pulse shaper circuit normalizes the amplitude of the input signal in such a way that it remains almost constant when the rotor speed changes and the corresponding changes in the frequency and amplitude of the signal at the sensor output. The table shows the amplitudes of the output signal of the sensor and the signal at the output of the low-pass filter at various rotor speeds at a cutoff frequency of the filter corresponding to a rotor speed of 1000 rpm.

n rpm 300 1000 5000 10,000 15,000 20000 30000 A Dan. AT 0.3 1,0 5,0 10.0 15.0 20,0 30,0 A fnch, B 0.287 0.707 0.981 0,995 0,998 0,999 0,999

In addition, the filter does not allow high-frequency interference to the input of the shaper. In fact, the low-pass filter performs the same functions as the volt-second area measurement unit, but using minimal circuit resources. The introduction of a low-pass filter into the shaper circuit eliminates one comparator, inverter, frequency and rate of change frequency meters, and a timer from the circuit.

Figure 2 shows the structural diagram of the proposed device pulse shaper from the signals of induction speed sensors. The device consists of an input low-pass filter 1, a comparator 2, a reference signal source 3, an analog multiplexer 4. The input of the low-pass filter 1 is connected to the output of the induction sensor. The output of the filter 1 is connected to the first input of the comparator 2, and the second input of the comparator 2 is connected to the source of the reference signal 3 by means of an analog multiplexer 4, to the control input of which the output signal of the driver is connected.

The bipolar signal of the induction speed sensor e _s is fed through the filter 1 to the first input of the comparator 2, and one of the threshold levels from the reference signal source 3 is fed to the second input of the comparator. The threshold level is selected by the analog multiplexer 4. The output of the comparator 2 is the output of the required pulse.

The comparator 2, the reference signal source 3 and the multiplexer 4 can be implemented as separate functional units or in hardware and software using a microcontroller, including a comparator, analog-to-digital and digital-to-analog converters.

The device operates as follows. At the beginning of the rising phase of the filter output signal, the comparator hysteresis threshold is high, then after reaching the filter output signal of the high threshold level, the comparator is triggered, and the hysteresis threshold is changed to low by the multiplexer. In the phase of decreasing the output signal of the filter, the comparator is activated after this signal reaches a low threshold level, after which the multiplexer connects a high hysteresis threshold level to the reference input of the comparator.

Thus, the introduction of an RC-type low-pass filter into the device with a cutoff frequency located in the lower region of the frequency range of the shaper provides high-frequency noise filtering and an almost constant amplitude of the output signal of the induction sensor in the entire range of rotational frequencies of the measured rotor, significantly simplifies the pulse shaper circuit and increases the reliability of its functioning.

Used sources

1. Sensors of thermophysical and mechanical parameters. Reference book. / Under the general editorship of Yu.N. Kopteva. Volume 1, M., publishing company of the journal "Radio Engineering", 1998, p. 52.

2. Horowitz P., Hill W. The art of circuitry. 5th ed., Volume 1, M .: Mir, 1998, p. 259.

3. Patent RU 2173022, C2, IPC7 H03K 5/153, publ. August 27, 2001

4. Patent RU 2399154, C1, IPC H03K 5/153, G01R 23/02, publ. 09/10/2010

Claims (1)

A pulse generator from signals of induction speed sensors, comprising a comparator and a reference voltage source, characterized in that an RC-type low-pass filter with a cut-off frequency located in the lower region of the frequency range of the driver is inserted into it, the filter input being connected to the output of the induction sensor, the output of the filter is connected to the first input of the comparator, and the second input of the comparator is connected to the source of the reference signal through an analog multiplexer, to the control input of which is connected yhodnoy signal generator.

Images