JPH09289791A - Load detection device for induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a load detection device for an induction motor having strong power supply voltage fluctuation, a high anti-noise characteristics against power supply line, a high operation speed, a good operation accuracy and a simple circuit. SOLUTION: A primary side of a transformer A (6) is connected to both the ends of capacitor (5), AC power supply (1) is connected for receiving power to the primary side of a transformer B (7), the starts of secondary sides of the transformer A (6) and transformer B (7) are coupled and connected, and the ends of the windings of both the transformers are connected to relay (8) and a variable resistor (9) for load level setting are connected. Therefore, the relay 8 is operated by the voltage for the difference between the transformers, and the connections are made for creating the difference in output between the transformers by considering the start and the end of the windings so as to have an opposite phase for the output voltages of both the transformers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load detecting device for a capacitor-operated single-phase induction motor.

[0002]

2. Description of the Related Art Conventionally, a load detecting device using an auxiliary winding of a capacitor-operated single-phase induction motor has been studied on the other side, and various detecting devices have been developed. As is well known, the load amount of a single-phase induction motor changes the voltage waveform and phase of the auxiliary winding, and the phase shift voltage applied to this auxiliary winding is half-wave rectified or full-wave rectified to obtain the sine of the power supply voltage. The phase shift time based on the wave zero crossing point, or the voltage was synthesized after rectification and detected by the phase shift time. In both cases, the detection process of the phase shift time after rectification causes noise especially on the power supply line. And the noise component is also rectified and becomes a combined voltage, which often makes it impossible to detect the load. In addition, the detection circuit is complicated and it greatly affects the fluctuation of the power supply voltage, resulting in poor operation accuracy. Further, since the phase shift time is detected, the detection time naturally becomes long when the phase shift time becomes long. As described above, in the prior art examples, JP-A-2-87989 and JP-A-1-238494 are used.
In each of the inventions, a detection device for half-wave rectifying the phase-shifted voltage applied to the auxiliary winding and thereafter measuring the phase-shifted time is disclosed.

[0003]

An object of the present invention is to provide a load detection device for an induction motor, which has a high operating speed, a high operating accuracy, a high power supply voltage fluctuation, a high power line noise resistance, and a simple device. is there.

[0004]

According to the present invention, a voltage applied to an auxiliary winding of a capacitor-operated single-phase induction motor or a capacitor serially connected to the auxiliary winding and a power supply voltage are received by individual insulating transformers. In addition, the secondary side of each isolation transformer and one line are coupled and connected, and the voltage of the difference between the transformers output from the other side of the secondary side of the isolation transformer is used as a relay. To operate. At this time, so that the output voltage of both isolation transformers are in opposite phase,
Connecting. By detecting the load of the induction motor by the above means, many problems can be solved.

[0005]

[Operation] When the load on the motor is lightened from the state where the relays are not operated by the output voltage difference between the insulation transformers when the load on the motor is heavy, the balance of the secondary side of each transformer is deviated and the voltage difference is generated. However, when a certain set level is reached, the relay operates. Power supply voltage fluctuation,
With regard to the action on the power line noise, since the insulation transformers are connected in reverse phase, the voltage of the output difference is not output and the relay is ineffective.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. The primary side of the transformer A (6) is connected to both ends of the capacitor (5), the AC power source (1) is connected to the primary side of the transformer B (7), and the secondary side of the transformer A (6) and the transformer B (7) is received. The winding start is connected and the other transformer is wound at the end of the relay (8) and the variable resistor (9) for setting the load level.
Is connected. With the above connection, the variable resistor (9) is set so that the relay (8) does not operate due to the difference in the secondary outputs of the transformer A (6) and the transformer B (7) when the load of the electric motor is usually heavy. The secondary voltage of transformer A (6) rises when the load of the electric motor becomes lighter from the state.
Since the difference with the voltage of (7) becomes large, the voltage of the difference between the transformers becomes large and the relay (8) operates. Regarding the power supply fluctuation, when the AC power supply (1) becomes higher, the voltage across the capacitor (5) also becomes higher and the transformer A
The secondary voltage of (6) also rises, but similarly the secondary voltage of transformer B (7) also rises, but both transformers A
Since (6) and transformer B (7) are connected in reverse phase, the rising output does not appear as a voltage difference and relay (8) does not operate. Conversely, when the power supply voltage drops, the same thing can be said as when the power supply voltage rises. Also from these things, even if noise is added to the power supply voltage, the transformer A
(6) By the reverse phase connection of transformer B (7), the output between the transformers does not appear as a voltage difference and the relay (8) does not malfunction. In this embodiment, the transformer A
(6), the voltage of the difference of the secondary voltage output from the transformer B (7) was directly detected by the relay (8), but using the comparator IC etc., the transformer A (6), the transformer B
It is also possible to compare and detect the voltage difference after the secondary voltage output from (7) and to output as non-contact.

[0007]

As is apparent from the above, as is apparent from FIG. 1, despite the simple circuit, it is resistant to power supply voltage fluctuations, has high resistance to power supply line noise, is capable of full-wave detection, has high operating speed, and has high operating accuracy. It can be said that this is a load detection device for an induction motor.

[Brief description of drawings]

FIG. 1 is an embodiment of the present invention.

[Explanation of symbols]

 (1) is an AC power source (2) is a main winding (3) is an auxiliary winding (4) is a single-phase induction motor (5) is a capacitor (6) is a transformer A (7) is Transformer B (8), relay (9), variable resistance (10), relay output contact

Claims (1)

[Claims] 1. A voltage applied to an auxiliary winding of a capacitor-operated single-phase induction motor or a capacitor connected in series to the auxiliary winding, and a power supply voltage are received by individual insulating transformers, and the voltage of each insulating transformer is received. Both the secondary side and one line are coupled and connected, and the relay is operated with a voltage corresponding to the difference between the transformers output from the other line on both the secondary side of the isolation transformer. Also, in order to make the output voltages of the two insulating transformers in opposite phases, the winding start and the winding end are taken into consideration, and wiring is performed so that a voltage corresponding to the difference is generated between the transformer outputs. A load detection device for an induction motor, characterized in that