JP2001281273A - Detection method for fan motor current and current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detection method which permits highly accurate detection of a drive current of a fan motor without variations and an apparatus therefor. SOLUTION: There are arranged an amplification circuit 3 to amplify an end-to-end voltage Vr of a resistor 2 connected in series to a fan motor 1, a triangular wave generation circuit 6 to generate a triangular wave voltage Vt and a comparator circuit 7 which compares the output voltage Vr' with the triangular wave voltage Vt to output a pulse signal of a duty ratio corresponding to the output voltage Vr'. Then, a microcomputer 5 computes the drive current of the fan motor 1 based on the duty ratio of the pulse signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting a fan motor current, and more particularly, to a method for detecting a fan motor current.
The present invention relates to an improved technology of a current detection device that connects a current detection resistor in series to a fan motor and detects a drive current of the fan motor based on a voltage between both ends.

[0002]

2. Description of the Related Art Conventionally, in the field of water heaters, a current detecting device as shown in FIG. 3A has been used for detecting a driving current of a fan motor for a blower. Specifically, the current detection device amplifies the voltage Vr across the resistor (current detection resistor) R connected in series with the fan motor a by the amplifier circuit b, and outputs the output voltage Vr 'of the amplifier circuit b. Is converted by a voltage / frequency conversion circuit (V / f conversion circuit) c into a pulse signal having a frequency f corresponding to the output voltage Vr ', and this pulse signal is input to a microcomputer d.

More specifically, in the current detecting device shown in FIG. 3A, the V / f conversion circuit c has a linear voltage-frequency characteristic (V / f characteristic) as shown in FIG. ) Is used. Therefore, the microcomputer d has the voltage Vr across the current detection resistor R.
(Accurately, a pulse signal having a frequency f proportional to the value of the output voltage Vr 'of the voltage amplifying circuit c) is supplied.

The microcomputer d takes in the pulse signal from the V / f conversion circuit c, finds the frequency f of the pulse signal, and drives the fan motor a based on the correlation between the frequency and the voltage-converted current. The current was calculated.

[0005]

However, in such a conventional current detecting device, the voltage value of the voltage Vr across the resistor R (specifically, the output voltage V
There is a problem that the input accuracy of the pulse signal taken into the microcomputer d varies depending on the level of (r ′).

[0006] First, the cause of variations in the input accuracy of the pulse signal will be described with reference to FIG.

FIG. 4 (a) shows a V / T characteristic diagram obtained by replacing the V / f characteristic diagram shown in FIG. 3 (b) with the relationship between voltage and period. In this case, the frequency f and the period T Is T = 1 / f
, The V / T characteristic becomes a non-linear characteristic as shown in the figure.

In FIG. 4A, the case where the voltage Vr across the resistor R is low and the case where the voltage Vr across the resistor R is high are indicated by points A and B, respectively. When the voltage Vr at the both ends is at the point A, the waveform of the pulse signal output from the V / f conversion circuit c is a pulse waveform having a long cycle as shown in FIG. Is at point B, a pulse waveform having a short cycle as shown in FIG.

In the conventional current detection device in which the voltage Vr across the resistor R is converted into such a pulse waveform, the voltage Vr across the current detection resistor R is A
When both points B and B increase by γ (in other words,
When the voltages change to A 'and B', respectively, due to the voltage fluctuation), the voltage fluctuation represented by γ appears as a change in the cycle T of the pulse signal (specifically, as a change indicated by α and β). Becomes In other words, in the conventional current detection device, even if the voltage fluctuation amount γ is the same, the change appearing in the cycle T of the pulse signal differs depending on the level of the voltage Vr between both ends (in the case shown, α> β). Becomes).

FIG. 4 (b) and FIG.
When expressed in (c), the waveform of each pulse signal appears as a change shown by a dotted line in the figure due to the voltage fluctuation amount γ. In the microcomputer d to which such a pulse signal is input, Since the pulse signal is only sampled at a fixed period (input voltage Vin is detected) (sampling state is indicated by an arrow in the figure), when the frequency of the pulse signal is high (FIG. 4 (c)). In some cases, the change in the pulse waveform due to the voltage fluctuation γ is narrower than the sampling timing, and the change in the waveform cannot be detected in some cases.

As described above, the driving current of the fan motor a is calculated based on the frequency f of the pulse signal obtained by converting the voltage Vr across the current detecting resistor R into V / f as in the conventional current detecting device. Therefore, there is a problem that the microcomputer d may not be able to accurately detect the waveform of the pulse signal depending on the value of the voltage Vr between both ends.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a current detection method capable of accurately detecting a drive current of a fan motor without variation, and an apparatus therefor. It is in.

[0013]

In order to achieve the above object, a current detecting device according to the present invention comprises a current detecting device for detecting a driving current of a fan motor based on a voltage across a resistor connected in series with the fan motor. A detection device, an amplifier circuit for amplifying a voltage between both ends of the resistor, a triangular wave generating circuit for generating a predetermined triangular wave voltage, and comparing an output voltage of the amplifier circuit and an output voltage of the triangular wave generating circuit. A current detection device comprising: a comparator circuit that outputs a pulse signal; and a microcomputer that calculates a drive current of the fan motor based on the pulse signal output from the comparator circuit.

That is, in this current detecting device,
The voltage Vr across the current detection resistor (resistor) R connected in series to the fan motor as a pulse signal input to a microcomputer that calculates the drive current of the fan motor.
The pulse signal having a constant period is obtained by comparing the output voltage Vr 'of the amplifier circuit (more precisely, it is indicated as Vr in the following description for convenience) with a predetermined triangular wave voltage Vt in a comparator circuit.

In this case, the voltage Vr is expressed linearly.
(Ie, the voltage rises proportionally over time)
(Repeat up and down) Compared to the triangular wave voltage Vt
The pulse signal output from the comparator circuit is
The on-time t corresponding to the level of the voltage Vr._onAnd oh
Time t_offRatio (duty ratio) changes proportionally
Will be. That is, if the voltage Vr increases,
ON time t of the pulse signal _onIs relatively extended
Off time t_offIs shortened, and conversely,
When the pressure Vr decreases, the on-time t_onIs relatively shortened,
With this, the off time t_offIs extended.
(See FIG. 2 (a)).

The microcomputer calculates the value of the both-ends voltage Vr from the pulse signal based on the characteristics of the pulse signal, and calculates the drive current of the fan motor from the value.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the current detecting device according to the present invention will be described below in detail with reference to FIGS.

FIG. 1 shows a case where the current detecting device according to the present invention is applied to the detection of a driving current of a fan motor 1 of a water heater, and the current detecting device is a resistor for detecting a current of the fan motor 1. , An amplifying circuit 3 for amplifying the voltage Vr across the resistor 2, and an output voltage Vr 'of the amplifying circuit 3.
A V / T converter 4 for converting the pulse signal into a pulse signal having a constant period,
A microcomputer 5 that calculates the drive current of the fan motor 1 based on the pulse signal output from the V / T converter 4 is configured as a main part.

The fan motor 1 is a DC motor for driving a blower fan of a water heater (not shown). The fan motor 1 has a DC voltage (DC 140
V) is applied.

The resistor 2 is a resistor connected in series with the fan motor 1. One end of the resistor 2 is connected to the fan motor 1 and the other end is connected to the ground. . Further, the amplifier circuit 3 includes the resistor 2
The amplifier circuit amplifies the voltage Vr between both ends to a voltage level that can be processed by the comparator circuit 6 described later.

The V / T converter 4 is a circuit for converting the output voltage Vr 'of the amplifier circuit 3 into a pulse signal having a constant period. The V / T converter 4 converts a predetermined triangular wave voltage. A triangular wave generating circuit 6 to be generated and a comparator circuit 7 for comparing the output voltage Vr 'of the amplifying circuit 3 with the triangular wave output of the triangular wave generating circuit 6 and outputting the pulse signal are mainly constituted.

The triangular wave generating circuit 6 is a circuit for repeatedly outputting a triangular wave voltage having a constant period as shown by a symbol Vt in FIG. 2 (a), and has a maximum value Vtmax of the triangular wave voltage Vt.
And the minimum value Vtmin is set to be wider than the expected fluctuation range of the output voltage Vr 'of the amplifier circuit 3. As the triangular wave generated by the triangular wave generating circuit 6, a sawtooth wave as shown in the figure is suitable,
As long as the waveform has a waveform in which the voltage changes proportionally with the passage of time, a waveform other than the above-mentioned sawtooth wave can be used.

On the other hand, the comparator circuit 7 is a circuit for comparing the output voltage Vr 'of the amplifying circuit 3 with the triangular wave voltage Vt. The comparison result of the comparator circuit 7 is shown in the lower column of FIG. A pulse signal as shown, more specifically, a pulse signal having the same period T as the triangular wave, and the ratio (duty ratio) between the on-time t _on and the off-time t _off is proportional to the output voltage Vr ′. A pulse signal that changes periodically is output.

This is because, in the current detection device of the present invention, the comparator circuit 7 uses the triangular wave voltage Vt whose voltage repeatedly rises and falls proportionally with time as the reference voltage to be compared with the voltage Vr. As a result, if the output voltage Vr 'rises, the on-time t _on of the pulse signal is relatively prolonged, while the off-time t _off is shortened.
Decreases, the on-time t _on is relatively shortened,
Accordingly, the off time t _off is extended. That is, the output voltage Vr 'is converted into a duty ratio of the pulse signal.

FIG. 2 shows a change in the fan motor current when the output voltage Vr 'is converted into a duty ratio of a pulse signal, that is, a change in the voltage Vr across the current detection resistor 2. Explanation will be made based on (b). FIG. 2 (b) illustrates the relationship between the voltage Vr across the resistor 2 (more precisely, the output voltage Vr 'of the amplifier circuit 3) and the off time t _off of the pulse signal.
In this case, the relationship between the voltage Vr across the resistor 2 and the off time t _off of the pulse signal has a linear characteristic as shown.

Therefore, under such a relationship, regardless of whether the voltage Vr across the resistor 2 is high or low (the case shown at points A and B in the figure), the voltage fluctuation occurring there The effect of the quantity γ on the pulse signal (that is,
The variation of the off time t _off ) is equal (α = β), and no variation occurs as in the conventional current detection device.

The output voltage Vr 'thus input to the V / T converter 4 is output as a pulse signal converted into a duty ratio, and is electrically insulated via a photocoupler (not shown). It is output to the microcomputer 5 in the state in which it is turned on.

On the other hand, the microcomputer 5 is an arithmetic unit for calculating the drive current of the fan motor 1 based on the pulse signal output from the comparator circuit 7. Specifically, based on the duty ratio of the given pulse signal, the microcomputer 5 calculates the processing in the comparator circuit 7 and the amplification factor in the amplifier circuit 3 back to calculate the current detection resistance 2 in the microcomputer 5. Is stored, and a program for calculating a current flowing through the fan motor 1 from the voltage Vr is stored. The drive current of the fan motor 1 is calculated according to this program. Alternatively, the drive current of the fan motor 1 may be uniquely obtained by using a reference table indicating the correlation between the current and the duty ratio obtained in advance by experiments.

The sampling timing of the pulse signal in the microcomputer 5 is a timing at which a change in the duty ratio of the pulse signal can be detected. More specifically, the waveform of the triangular wave voltage Vt (that is, FIG. It goes without saying that a microcomputer with appropriate timing is appropriately used in accordance with (a) the inclination of the triangular wave).

As described above, according to the current detecting device of the present invention, the voltage Vr across the current detecting resistor 2 is converted by the comparator circuit 7 into a pulse signal having a duty ratio corresponding to the voltage value, and transmitted to the microcomputer. Since the voltage is input, the influence of the fluctuation of the above-mentioned voltage Vr (more precisely, the output voltage Vr 'of the amplifier circuit 3) on the pulse signal is always constant, and it is possible to provide a current detecting device having no variation in accuracy. it can.

The above-described embodiment shows a preferred embodiment of the present invention, and the present invention is not limited to the above-described embodiment, and various design changes can be made within the scope of the present invention. is there.

For example, in the above embodiment, the comparator circuit 7 outputs the pulse signal when Vr '> Vt, but it is of course possible to output the pulse signal in this case.

Further, in the above embodiment, the case where the current detecting device of the present invention is applied to the fan motor current detection of the water heater is shown. The present invention can be applied to a motor other than the motor.

[0034]

As described above in detail, according to the fan motor current detecting method and the current detecting device of the present invention, the voltage between both ends of the current detecting resistor connected in series with the fan motor is set to a predetermined triangular wave voltage. Is converted into a pulse signal having a duty ratio corresponding to the voltage value of the both-ends voltage, and the drive current of the fan motor is calculated based on the duty ratio of the pulse signal. Irrespective of the magnitude of the signal, that is, regardless of the level of the voltage between both ends of the current detecting resistor, the accuracy of capturing the pulse signal into the microcomputer can be kept constant.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a current detection device according to the present invention.

FIG. 2 is an explanatory diagram showing an operation of a comparator circuit in the current detection device. FIG. 2A shows a relationship between a voltage waveform input to the comparator circuit and a pulse waveform output, and FIG. b) is an explanatory diagram showing a relationship among an off time, a current detection resistor, and a voltage between both ends in the same pulse waveform.

FIG. 3 shows a conventional current detection device, FIG. 3 (a) is a block diagram showing a schematic configuration of the current detection device, and FIG. 3 (b) is a V / f conversion circuit in the current detection device. V /
The f characteristic is shown.

4A and 4B are explanatory diagrams illustrating the operation of the conventional current detection device. FIG. 4A is a characteristic diagram in which the V / f characteristic shown in FIG. FIG. 4 (b)
FIG. 4C is a time chart showing the waveform of the pulse signal input to the microcomputer and the sampling timing.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fan motor 2 resistor (current detection resistor) 3 amplifier circuit 4 V / T converter 5 microcomputer 6 triangular wave generation circuit 7 comparator circuit Vr voltage across current detection resistor Vr ′ amplifier circuit output voltage Vt triangular wave voltage

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Kimura 93 Edo-cho, Chuo-ku, Kobe-shi, Hyogo Prefecture Inside Noritz Co., Ltd. (72) Inventor Mamoru Miyazaki 93 Edo-cho, Chuo-ku, Kobe-shi, Hyogo Noritz Co., Ltd. (72) Inventor Iwao Yoneda 93, Edocho, Chuo-ku, Kobe, Hyogo Prefecture Inside Noritz Co., Ltd. (72) Inventor Masaki Takada 93, Edocho, Chuo-ku, Kobe City, Hyogo Prefecture Noritsu Co., Ltd. (72) Inventor Tomoki Kishimoto 93, Edo-cho, Chuo-ku, Kobe-shi, Hyogo Pref. In Noritz, Inc. (72) Inventor Takeshi Morikawa 93, Edo-cho, Chuo-ku, Kobe, Hyogo, Japan Noritsu, Inc. (72) Inventor Masahiro Mori, Kobe, Hyogo Pref. 93F, Edo-cho, Chuo-ku F-term in Noritz Co., Ltd. (reference) 2G035 AA17 AB04 AC04 AD23 AD28 AD52 AD56

Claims (3)

[Claims] 1. A method for detecting a drive current of a fan motor, comprising: comparing a voltage between both ends of a current detection resistor connected in series with the fan motor with a predetermined triangular wave voltage; A method for detecting a fan motor current, comprising: converting a pulse signal having a duty ratio corresponding to a value into a pulse signal; and calculating a drive current of the fan motor based on the duty ratio of the pulse signal. 2. A current detection device for detecting a drive current of a fan motor based on a voltage across a resistor connected in series with the fan motor, comprising: an amplifier circuit for amplifying a voltage across the resistor; A triangular-wave generating circuit that generates a triangular-wave voltage, a comparator circuit that compares an output voltage of the amplifying circuit with an output voltage of the triangular-wave generating circuit, and outputs a pulse signal, based on a pulse signal output from the comparator circuit. And a microcomputer for calculating a drive current of the fan motor. 3. The current according to claim 2, wherein a voltage range between a minimum value and a maximum value of the triangular wave voltage is set to be wider than a fluctuation width of an output voltage of the amplifier circuit. Detection device.