SU135529A1 - Static non-contact frequency sensor for asynchronous motor speed - Google Patents

Description

The described sensor relates to the known static contactless frequency sensors for asynchronous motor speed, containing inductance and capacitance, which form an oscillating circuit with a natural frequency equal to the rotor frequency of the motor being controlled in nominal mode.

In order to increase the accuracy and reliability of operation in the described sensor, the output is formed from two active resistances connected via diodes to different plates of an oscillating circuit capacitor. In this way, an output current is obtained, the magnitude and sign of which varies with the magnitude and sign of the frequency.

To regulate the setpoint frequency, the capacitors are made partitioned and a saturation throttle is connected at the input of the oscillating circuit.

FIG. 1 shows a diagram of the described sensor; in fig. 2 - vector diagrams with resonant frequency; in fig. 3 - the same, with a deviation from the resonant frequency; in fig. 4 - the characteristic of the described sensor; in fig. 5 is a diagram of connecting a sensor to an asynchronous motor; in fig. 6 - the structure of the sensor magnetic circuit; in fig. 7 shows a variant of connecting a sensor with intermediate magnetic amplifiers.

The principle of operation of the described sensor is based on the resonant properties of an oscillating circuit containing inductance and capacitance.

An alternating frequency L / 1 with a variable frequency f (Fig. 1) is applied to the coil LI, magnetically coupled to the coil La. A signal proportional to the frequency deviation is removed from the load resistances.

No. 135529-2 and connected to the clamps of the oscillating circuit LgC through rectifiers B.

The sensor operation is explained by the vector diagrams in FIG. 2. The current / 1 and the flow 01 in the LI coil are 90 ° behind the applied voltage UL. Part of the flow F1 covers the coil Lg of the oscillating circuit and induces an emf in it. 21- At resonance, the resistance of the second series circuit is purely active, and therefore the current vector / 2 coincides in phase with 21, and the voltage t / 2 on the coil Lg must advance current / 2 by 90 °. The windings of the circuits are interconnected so that at resonance on the load resistances "i and K", equal voltages U and U develop, and the voltage U, between points a and b, determined by the difference U "-U. ,, to zero.

When the voltage frequency U deviates from the resonant re ultirush, its resistance of the second loop LgC becomes complex, with a predominance of inductive or capacitive components depending on the increase or decrease in frequency. If the frequency is powered: its voltage is greater than the resonant frequency of the LgC circuit (Fig. 3), the current vector / 2 lags 21 by an angle φ determined by the component of their complex resistance of this circuit. As a result of the rotation of current ig, the voltage f / 2 turns at the same angle relative to the flow F. The voltage f / ag is excellent from zero to zero. The greater the deviation of the frequency / 1 of the supply voltage from the resonant / o, the greater the angle f of the rotation of the vectors / 2 and Uz and the difference in the voltages U "- / 7", increases. This dependence determines the linear portion of the characteristic of the sensor A / dg / wi - / 2 depending on the frequency (Fig. 4). A part of the characteristic shows that with a significant deviation of A / frequency from the resonant resistance of the second circuit, which at the resonance was minimal and purely active, it increases and the current / 2 decreases. In addition, the frequency deviation from the resonance leads to a decrease in the input resistance of the sensor and, consequently, to an increase in current / 1. In the presence of a power source impedance, the increase in current ii causes a decrease in U and,.

In a closed-loop control system, the frequency sensor of the PDS speed is powered from the rings of the asynchronous motor BP, and its load is the control windings of the intermediate magnetic amplifiers of the PMU (Fig. 5). The voltage frequency at the rotor clamps is proportional to the speed of the engine turn. Therefore, the output signal of the speed sensor is proportional to the deviation of the engine speed from the set one. In this case, the polarity of the signal provides an increase or decrease in the speed of the engine operating in a closed control system. The frequency sensor speeds the PDS in a closed system makes it possible to adjust the resonant frequency, thereby providing the speed control of the asynchronous motor. The resonant frequency of the sensor is adjusted by changing the capacitance (in steps) or inductance (smoothly). In the first case, capacitors are switched. In the second case, the bias winding current Wn changes (Fig. 6).

The frequency sensor is made on two magnetic cores assembled from W-shaped iron, and the bias winding Wn is located on the magnetic inserts between the cores. Such a sensor design makes it possible to perform DC magnetization without induction of a variable emf. in the winding of magnetization.

The coupling of a frequency sensor with intermediate magnetic amplifiers can be carried out as shown in FIG. 1, including control windings on terminals a and b. However, a higher efficiency. is obtained by applying a circuit by magnetic summation (Fig. 7). To cast

sensor operation in accordance with the resistance of the windings of the magnetic amplifier applied a separate primary winding and made tap-offs from the winding of the oscillating circuit.

Subject invention

Claims (2)

1. A static non-contact frequency speed sensor for an asynchronous motor containing inductance and capacitance forming an oscillating circuit with a natural frequency equal to the rotor frequency of the monitored motor in nominal mode, characterized in that, in order to increase accuracy and reliability, the output of the sensor is formed from two active resistances connected via diodes to different capacitor plates of the oscillating circuit to obtain an output current, the magnitude and sign of which depends on the magnitude and sign of the change Frequencies. 2. A sensor according to claim 1, characterized in that, in order to adjust the frequency setting, the capacitors are made partitioned and a saturation choke is turned on at the input of the oscillating circuit. and, and,  8s. Jhz t PMUP