CN1287272A - DC motor speed detection device - Google Patents

Abstract

A direct current motor rotating speed detection device comprises a pulse wave coupler, a click circuit, a speed measurement circuit, a comparator and an alarm, wherein the pulse wave coupler is electrically connected with a power line of a direct current motor, the pulse wave coupler, the click circuit, the speed measurement circuit, the comparator and the alarm are sequentially electrically connected, the click circuit is triggered by the pulse wave coupler to generate square wave voltage to be detected, the speed measurement circuit converts the square wave voltage output by the click circuit into a voltage value to be detected, the comparator is used for comparing the voltage value to be detected and outputting a low rotating speed signal when the voltage to be detected is lower than a critical voltage, and the alarm outputs an alarm signal when receiving the low rotating speed signal output by the comparator.

Description

DC motor speed detection device

The invention relates to a speed detection device of a direct current motor, in particular to a speed detection device of a direct current motor which does not need to be changed and has low cost; the speed detection device of a direct current motor is especially suitable for a fan.

Electronic instruments and equipment often need to use fans to dissipate heat to avoid damage caused by overheating, so that electronic instruments can operate normally. However, after a period of use, the DC motor used on the fan will be damaged due to the wear of the motor's own shaft or other Mechanical reasons cause the speed of the motor to drop, which greatly reduces the cooling efficiency provided by the fan driven by it, and even causes the equipment using the fan to fail or be damaged. Therefore, it is necessary to monitor the speed of the DC motor. Generally, there are two main technologies used to monitor the speed of DC motors used in fans. One is the optical coupling method, and the other is the magnetic field induction method. However, when these two methods are implemented, the device of the DC motor must first be A certain degree of change is required, and the cost of the components is relatively high, so it is inconvenient neither for the manufacturer nor the user of the DC motor.

The object of the present invention is to provide a low-cost DC motor rotational speed detection device without changing the DC motor device.

To achieve the above object, the present invention takes the following measures:

The DC motor rotational speed detecting device of the present invention is characterized in that it comprises a pulse wave coupler, a click circuit, a speed measuring circuit, a comparator and a warning device;

The pulse wave coupler is electrically connected with the power line of the DC motor, and outputs a coupling voltage;

The click circuit is electrically connected to the pulse wave coupler, and is triggered by the coupling voltage of the pulse wave coupler to generate a square wave voltage to be measured;

The speed measuring circuit is electrically connected with the click circuit, and is used to convert the square wave voltage to be measured output by the click circuit into an analog voltage value to be measured;

The comparator is electrically connected with the speed measuring circuit and has a critical voltage value for receiving and comparing the voltage value to be measured output by the speed measuring circuit, and can output a low voltage value when the voltage value to be measured is lower than the analog critical voltage value Speed signal;

The warning device is electrically connected with the comparator, and can output a warning signal when receiving the low speed signal output by the comparator.

Wherein: the warning device can be a buzzer.

Wherein: the warning device can be a light emitting element.

Wherein: the threshold voltage value may be an analog threshold voltage value.

Wherein: the threshold voltage value may be a digital threshold voltage value.

Below in conjunction with accompanying drawing and embodiment the present invention is described in detail:

Description of drawings:

Fig. 1 is a circuit block diagram of an embodiment of the present invention.

Fig. 2 is a circuit diagram of an embodiment of the device for detecting the rotational speed of a DC motor according to the present invention.

Fig. 3 is a schematic perspective view of an embodiment of the present invention.

Fig. 4 is a schematic diagram of a current waveform of a DC motor power line according to an embodiment of the present invention.

As shown in Figures 1 to 3, the DC motor speed detection device of the present invention is implemented on a fan 1 using a DC motor, and the fan 1 includes a fan body 10, a DC motor 20 and a DC motor speed detection device 30. The motor 20 is used to drive the fan body 10, and the DC motor speed detection device is connected in series with the external power supply line 21 of the DC motor 20. The DC motor speed detection device 30 can be connected externally to the fan 1, or directly as shown in FIG. It is installed at a proper position in the fan body 10 and together forms a part of the fan 1 .

The DC motor 20 can be a brushless DC motor or a brushed DC motor. According to the characteristics of the DC motor, the current waveform on its power line 21 will be a continuous negative pulse as shown in FIG. 4 .

As shown in FIGS. 1 and 2 , the DC motor speed detection device 30 includes a pulse coupler 31 , a click circuit 32 , a speed measuring circuit 33 , a comparator 34 and a warning device 35 .

The pulse wave coupler 31 is electrically connected to the power supply line 21 of the DC motor 20 .

The click circuit 32 is electrically connected with the pulse wave coupler 31, and is triggered by the coupling voltage of the pulse wave coupler 31 to generate a square wave voltage to be measured. The square wave voltage to be measured is a continuous square wave with a certain width. When the DC motor The higher the rotation speed of 20, the smaller the distance between the square wave and the square wave, so the higher the average voltage value, and vice versa.

The tachometer circuit 33 is electrically connected with the single-click circuit 32, in order to process the square wave pulse voltage to be measured output by the single-click circuit 32 in an analog (or digital) manner, and convert it into an analog voltage value to be measured (or into a digital average count value to be tested).

The comparator 34 is electrically connected with the tachometer circuit 33 and presets a critical voltage value (or critical value) for receiving the voltage value to be measured output by the tachometer circuit 33 and comparing it. When the voltage value to be measured output by the tachometer circuit 33 is low At the critical voltage value (or the measured average count value output by the speed measuring circuit 33 is lower than the critical value), a low speed signal is output in response. The critical voltage value and the critical value are set according to the minimum required output speed of the DC motor 20 .

The warning device 35 is electrically connected with the comparator 34, and when receiving the low speed signal output by the comparator 34, it will output a warning signal in response.

In the present embodiment, the pulse wave coupler 31 mainly includes three transistors Q1, Q2, Q3, two resistors R1, R2 and a capacitor C1, and the transistor Q2 is directly electrically connected with the power line 21 of the DC motor 20; C1 outputs a coupling voltage.

The click circuit 32 mainly includes two transistors Q4, Q5, five resistors R3, R4, R5, R6, R7 and a capacitor C2, wherein the resistor R3 is directly electrically connected with the capacitor C1 of the pulse coupler 31, and is subjected to Triggered by the coupling voltage output by the capacitor C1, a square wave voltage to be measured is generated. The square wave voltage to be measured is a continuous square wave with a certain width. If the rotational speed of the DC motor 20 is higher, the distance between the square wave to be measured and the square wave The smaller the spacing, the higher the average current, and vice versa.

The speed measuring circuit 33 mainly includes a resistor R8 and a capacitor C3, wherein the resistor R8 is directly electrically connected to the resistor R6 of the click circuit 32, and the speed measuring circuit 33 can output the square wave pulse to be measured via the resistor R6 The wave voltage is processed in an analog or further digital manner, and converted into an analog voltage value to be measured or further converted into a digital average count value to be measured.

The comparator 34 mainly includes two operational amplifiers and four resistors R9, R10, R11, R12. The comparator 34 is directly electrically connected to the speed measuring circuit 33, and is predetermined to have a critical voltage value or a critical value. If the speed measuring circuit 33 outputs The average count value of the voltage to be measured is lower than the critical voltage value, or the average count value to be measured output by the speed measuring circuit 33 is lower than the critical value, then a low speed signal is output; the critical voltage value and the critical value are based on the required The output minimum speed is set.

Compared with the prior art, the present invention has the following effects:

As can be seen from the above, when the DC motor 20 is used for a long time, its rotating shaft (not shown) is worn and the output speed of the DC motor 20 is reduced, as shown in FIG. 4 , in the current waveform on the power line 21, The interval L1 between two consecutive negative pulses will become longer, and the interval L2 between two consecutive square waves will be relatively longer when coupled to the square wave voltage to be measured output by the click circuit 32 via the pulse wave coupler 31. Therefore, The analog average DC voltage value will decrease (or the digital average count value will decrease), and also the voltage value to be measured (or the average count value to be measured) converted by the speed measuring circuit 33 will decrease thereupon, once the simulated voltage value to be measured Below the preset critical voltage value (or when the digital average count value to be measured is lower than the preset critical value), the comparator 34 outputs a low speed signal to the warning device 35, so that the warning device 35 emits a sound or lights, etc. Warning signal, like this, once the rotating speed of DC motor 20 reduces and causes the cooling function provided by fan 10 to be not good, the user just can receive warning immediately, and carry out maintenance or replacement work, avoids the instrument or the instrument that uses fan 10 as heat dissipation tool Equipment failure or damage. It can be seen from the above device that there is no need to change the device of the DC motor during implementation, and the cost of the required components is relatively low.

Claims (5)

1. A DC motor speed detection device, characterized in that it includes a pulse wave coupler, a click circuit, a speed measuring circuit, a comparator and a warning device; The pulse wave coupler is electrically connected with the power line of the DC motor, and outputs a coupled voltage; The click circuit is electrically connected to the pulse wave coupler, and is triggered by the coupling voltage of the pulse wave coupler to generate a square wave voltage to be measured; The speed measuring circuit is electrically connected with the click circuit, and is used to convert the square wave voltage to be measured output by the click circuit into an analog voltage value to be measured; The comparator is electrically connected with the speed measuring circuit and has a critical voltage value for receiving and comparing the voltage value to be measured output by the speed measuring circuit, and can output a low voltage value when the voltage value to be measured is lower than the analog critical voltage value Speed signal; The warning device is electrically connected with the comparator, and can output a warning signal when receiving the low speed signal output by the comparator. 2. The DC motor speed detection device as claimed in claim 1, characterized in that: The warning device is a buzzer. 3. The DC motor speed detection device as claimed in claim 1, characterized in that: The warning device is a light emitting element. 4. The DC motor speed detection device as claimed in claim 1, characterized in that: The threshold voltage value is an analog threshold voltage value. 5. The DC motor speed detection device as claimed in claim 1, characterized in that: The threshold voltage value is a digital threshold voltage value.

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