SU407234A1 - DEVICE FOR MEASURING ROTATION SPEED - Google Patents

Description

The invention relates to the field of measurement and control of motion parameters and can be used to measure the rotational speed of three-phase asynchronous hermetic motors with a short-circuited rotor. Devices for measuring the rotational speed of an electric motor are known, comprising a power source associated with the motor windings through an interrupter, a series-connected amplifier, a key and a measuring device, as well as a control circuit connected to the interrupter and the key. In order to improve the measurement accuracy, the proposed device is equipped with an error control device, the input and output of which are respectively connected to a measuring device connected to the control circuit. FIG. 1 is a block diagram of the described device; in fig. 2 shows plots of the measurement speed error versus the motor tripping time, proportional to the averaging coefficient, and the velocity measurement error to the measurement time, inversely proportional to the averaging coefficient; in fig. 3 - time diagrams of voltages. The device contains an interrupter 1 consisting of triac keys and connected between a power source, an electric motor 2 and an amplifier 3, which is a low-frequency amplifier-limiter with a high-resistance input on field-effect transistors. The output of amplifier 3 via switch 4, which consists of a triac switched by control circuit 5, is loaded on measuring device 6. The latter consists of a circuit measuring the input signal period, or an average of n periods, and a circuit that regulates the measurement time on command from the instrument 7 for error control. The device b is connected to the input of the control circuit 5, consisting of a stable electronic time relay with continuously adjustable exposure, setting the measurement rhythm, a multivibrator operating in a decelerated mode to eliminate the influence of the damped electromagnetic field on the measurement accuracy, and opening the breaker after the end of the measurement process. Acquisition 7 consists of a scheme comparing the value of the period T with the predetermined value of the period Gz and carries out an increase in the averaging coefficient as soon as. The operation of the device is based on turning off the power of the electric motor with subsequent measurement of one or the average of the n periods by induction in the winding e. d. The error of the measured period is: 8: 8p + SOT,

 ± (a

5 "+

/ ome

where the bot is the error due to the decrease in speed when working on the coasting;

BT - the error of the measuring device;

bq, the rms error of the nominal frequency setting of the internal crystal oscillator or the reference frequency of the external source;

/ o is the frequency of filling the measured period, kHz;

Tism - 3 readings of the measured period, ms;

n is the period averaging coefficient.

The selection of the maximum value of the averaging coefficient is made according to the graph of FIG. 2

The intersection point of the curve /, showing the dependence of the measurement error on the motor off time, proportional to the averaging coefficient η, and curve II, showing the dependence of the measurement error on the measurement time, inversely proportional to the averaging coefficient η, determines the maximum value of the averaging coefficient Pmax-Max. in the following way.

Breaker 1 supplies a three-phase voltage to the motor 2 when the control circuit 5 is turned on. After a time equal to the time delay of the time relay, the control circuit 5 generates a blocking voltage to the breaker 1, thereby disconnecting the power from the motor 2. This voltage, but delayed time goes to the control input of the key 4, which begins to pass an amplified signal to the input of the measuring device 6. The latter produces a pulse, the duration of which is equal to the time

measurement and which is fed to the input of the control circuit 5. The falling edge of this pulse generates the unlocking voltage of the interrupter 1, the locking voltage of the key 4 and returns the electronic time relay of the control circuit 5 to its initial state. Before starting the measurement, given the required measurement accuracy, set the duration of the measured period Gyzm, at which the measuring device 6 reaches

the command from the device 7 increases the coefficient

averaging. Measurement error in this case.

remains unchanged.

FIG. Figure 3 shows time diagrams of voltages (the first pulse for the value of the averaging coefficient n-il, the second for dL), where Za is the voltage of the electric motor; 36 — pulses, control circuits 7 arriving at the control inputs of the chopper 1; Sv - pulses from control circuit 5 to 1 switch 4 and from the stroke of the measuring device 6 to the input of the control circuit; Зг - impulse from the device 7 to the measuring device; Zd - induced in

winding e. d. after disconnecting the pitapi motor.

The subject invention "1i

An apparatus for measuring the rotational speed of an electric motor, comprising a power source connected to the motor windings through an interrupter, a series-connected amplifier, a key and a measuring device, as well as a control circuit connected to the interrupter and the key, in order to improve the measurement accuracy, it is equipped with an instrument for controlling the error, the INPUT and the output of which are respectively connected to a measuring instrument connected to the control circuit.

-0 p.

Max.