CN108196115B - Zero point adjusting method and circuit of digital direct current clamp meter - Google Patents

Abstract

The invention relates to a zero point adjusting method of a digital direct current clamp meter, which comprises a Hall sensor, a differential amplifying circuit, a controller MCU, a zero point key and a display screen LCD; the zero point adjusting method comprises the following steps: step one, starting a digital direct current clamp meter to perform zero setting test, and pressing a zero setting button to perform zero setting when the display value of the display screen LCD is not zero during no-load measurement; step two, after triggering the zero setting key, the controller MCU reads the zero value and polarity, and outputs a signal which is continuously increased and has opposite polarity to the input end of the differential amplifying circuit, so that the value output by the differential amplifying circuit is reduced until the zero value read by the controller MCU is zero; and thirdly, when the zero point value is read to be zero, the controller MCU records the output value at the moment, stores the output, stops the zeroing action and completes zeroing.

Description

A zero-point adjustment method and circuit for a digital DC clamp meter

Technical field

The invention belongs to the technical field of electronic measurement, and specifically relates to a zero point adjustment method and circuit of a digital DC clamp meter.

Background technique

The digital DC clamp meter is an instrument that uses the magnetoelectric conversion characteristics of the Hall sensor to measure DC voltage; when the measured (primary) wire passes through the voltage sensor, the measured voltage I will generate magnetic lines of force, and the primary side The magnetic field lines are concentrated around the CT air gap. The Hall chip built into the magnetic core air gap can generate an induced voltage of only a few millivolts that is proportional to the primary magnetic field lines. This tiny signal is amplified through subsequent electronic circuits. And converted into corresponding numbers, the value of the voltage I of the energized conductor can be measured. However, there is an offset voltage in the operational amplifier in the Hall element and the electronic circuit, so that when the measured voltage I is zero, the operational amplifier output still has a tiny voltage. Moreover, the characteristics of the Hall device cause the offset voltage to change when the temperature of its surrounding environment changes.

Therefore, digital DC clamp meters using Hall sensors require methods and circuits to process the measurement zero point; however, there are two traditional zeroing methods:

One is to use hardware zero adjustment method, as shown in Figure 1. The zero point adjustment circuit is composed of VR1, R5, R4, and R6. VR1 is connected to the positive and negative power supplies. A certain voltage is obtained at the slide end. After being divided by R5\R6, the differential is input through R4. Amplifier A adjusts the Vo value. Since the slide end can obtain positive and negative voltages, adjust Vo to 0. Figure 1 uses an adjusting potentiometer to adjust the zero point of the amplifier. The potentiometer knob is set outside the instrument. Disadvantages: 1. During use, it is easily affected by the vibration of the instrument operation, causing the zero point to shift, causing reading errors and making use troublesome; 2. Hall devices The consistency is poor, and the zero-point adjustment range needs to be maintained within a certain range. During production, it must be pre-adjusted within the instrument according to different Halls. Mass production is difficult and inefficient.

The other method is to use software zero adjustment, as shown in Figure 2. It is a software zero adjustment method. The MCU directly reads the zero value and saves it. The MCU's calculation function is used to directly deduct the zero point from the measured amplifier output value. The numerical value is the voltage value. This method of relative value measurement is simple. However, using the relative value measurement method, since the input of zero-point voltage sometimes seriously affects the MCU measurement range, this zero-point voltage can only be used within a small range. Therefore, it still needs a zero-adjustment circuit inside so that the output zero point of the amplifier can be within the measurement range of the MCU. Compared with the previous one, the zero-adjustment device is a variable resistor inside the instrument and is not easily affected by the operation of the instrument. Therefore, the hardware circuit still performs a pre-correction operation on the zero point during production, and the measurement range will be affected by the zero point operation. For example, the voltage range measured by FS9721 is ±400mV. If the input Vo exceeds the range of ±400mV, it cannot be tested, and the LCD displays "OL" (overflow). Therefore, if Vo does not return to zero when the value is 20mV, the voltage measured by the instrument is converted to a maximum voltage of only 380mV. Reduce the measuring range of the instrument.

Contents of the invention

In order to solve the problems existing in the above-mentioned prior art, the present invention provides a zero-point adjustment method and an adjustment circuit of a digital DC clamp meter to overcome the shortcomings of the zero-point adjustment of the traditional digital DC clamp meter in use and production. There is no need to use a potentiometer for adjustment and it does not affect the measurement range.

The technical solution of the present invention is as follows:

Technical solution one:

A zero point adjustment method for a digital DC clamp meter. The digital DC clamp meter includes a Hall sensor, a differential amplifier circuit, a controller MCU, a zero point button and a display LCD; the Hall sensor generates a measurement voltage and Input to the input end of the differential amplifier circuit, the output end of the differential amplifier circuit is connected to the controller MCU, the zero point button is connected to the controller MCU, and the display screen LCD is connected to the controller MCU; The zero point adjustment method described above includes the following steps:

Step 1. Start the digital DC clamp meter for zero adjustment test. When the LCD display value is not zero during no-load measurement, press the zero button to perform zero adjustment;

Step 2. After triggering the zero point button, the controller MCU reads the zero point value and polarity, and outputs a continuously increasing signal with opposite polarity to the input end of the differential amplifier circuit, making the output value of the differential amplifier circuit smaller until The zero point value read by the controller MCU is zero;

Step 3: When the zero point value is read as zero, the controller MCU records the output value at this time and saves the output, stops the zero adjustment action, and completes the zero adjustment.

Further, in step two, the output circuit of the controller MCU is equipped with a D/A converter. After the zero point button is triggered, the controller MCU reads the zero point value and polarity, and outputs a continuously increasing, polarity The opposite digital signal is sent to the D/A converter. The D/A converter converts the digital signal into a continuously increasing voltage signal with opposite polarity and outputs it to the differential amplifier circuit, making the output value of the differential amplifier circuit smaller. , until the zero point value read by the controller MCU is zero.

Alternatively, in step two, the output circuit of the controller MCU is equipped with a PWM generator. After the zero point button is triggered, the controller MCU reads the zero point value and polarity, and outputs a continuously increasing, opposite polarity The digital signal is sent to the PWM generator. The PWM generator converts the digital signal into a pulse signal with a gradually increasing duty cycle. After filtering, the pulse signal generates a continuously increasing voltage signal with opposite polarity and outputs it to the differential amplifier. circuit to make the value output by the differential amplifier circuit smaller until the zero point value read by the controller MCU is zero.

Technical solution two:

The invention also includes a zero-point adjustment circuit of a digital DC clamp meter, including a Hall sensor, an operational amplifier, an integrated chip, a display screen LCD, a zero-point adjustment unit and a zero-adjustment button; the integrated chip includes a controller MCU, a /D converter, memory, output unit, keyboard processing unit and LCD driving unit, the A/D converter, memory, output unit, keyboard processing unit and LCD driving unit are all electrically connected to the controller MCU; The two output terminals of the Hall sensor are respectively connected to the forward input terminal and the reverse input terminal of the operational amplifier through resistors R1 and R2, and the output terminal of the operational amplifier is connected to the A/D converter of the integrated chip. The output terminal of the operational amplifier is connected to the forward input terminal of the operational amplifier via resistor R3; the output unit is electrically connected to the reverse input terminal of the operational amplifier via resistors R5 and R4, and the resistor between R4 and R5 The line is connected to the signal ground via resistor R6.

Further, a capacitor C1 is connected in parallel to both ends of the resistor R6.

The invention has the following beneficial effects:

1. The circuit does not have a potentiometer, so there is no need to adjust the zero return circuit parameters;

2. Since Vo=0 after entering the test state, the entire test circuit will not affect the test range of the MCU;

3. Resistors R5 and R6 divide the zero-adjustment signal to make the zero-adjustment more precise and precise;

4. Add capacitor C1 to filter the zeroing signal to make the signal more stable.

Description of drawings

Figure 1 is an implementation circuit diagram of the first solution in the prior art;

Figure 2 is an implementation circuit diagram of the second solution in the prior art;

Figure 3 is a functional block diagram of Embodiment 1 of the present invention;

Figure 4 is a schematic block diagram using a D/A converter solution;

Figure 5 is a schematic block diagram of a PWM generator solution;

Figure 6 is a functional block diagram of Embodiment 2;

Figure 7 shows the voltage waveform using a D/A converter;

Figure 8 shows the voltage waveform using a PWM generator.

The reference marks in the figure are:

1. Hall sensor; 11. Operational amplifier; 12. Integrated chip; 121. A/D converter; 122. Memory; 123. Output unit; 124. Keyboard processing unit; 125. LCD drive unit; 13. Zero point adjustment unit ; 2. Differential amplifier circuit; 3. Controller MCU; 4. Zero button; 5. Display LCD; 6. D/A converter; 7. PWM generator.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Example 1:

Referring to Figures 3 to 5, a zero point adjustment method of a digital DC clamp meter is shown. The digital DC clamp meter includes a Hall sensor 1, a differential amplifier circuit 2, a controller MCU3, a zero point button 4 and a display screen LCD5. ; The Hall sensor 1 generates a measurement voltage and inputs it to the input end of the differential amplifier circuit 2, the output end of the differential amplifier circuit 2 is connected to the controller MCU3, and the zero point button 4 is connected to the controller MCU3 , the display screen LCD5 is connected to the controller MCU3; the zero point adjustment method includes the following steps:

Step 1. Start the digital DC clamp meter for zero adjustment test. When the display LCD5 displays a value other than zero during no-load measurement, press zero button 4 to perform zero adjustment;

Step 2. After triggering the zero point button 4, the controller MCU3 reads the zero point value and polarity, and outputs a continuously increasing signal with opposite polarity to the input end of the differential amplifier circuit 2, so that the value output by the differential amplifier circuit 2 becomes Small until the zero point value read by controller MCU3 is zero;

Step 3: When the zero point value is read as zero, the controller MCU3 records the output value at this time and saves the output, stops the zero adjustment action, and completes the zero adjustment.

Further, in step two, the output circuit of the controller MCU3 is equipped with a D/A converter 6. After the zero point button 4 is triggered, the controller MCU3 reads the zero point value and polarity, and outputs a continuously increasing, The digital signal with opposite polarity, such as "0000 0001-0000 0010-0000 0011..." is sent to the D/A converter 6, and the D/A converter 6 converts the digital signal into a continuously increasing voltage with opposite polarity. The signal is output to the differential amplifier circuit 2, so that the value output by the differential amplifier circuit 2 becomes smaller until the zero point value read by the controller MCU3 is zero.

Alternatively, in step 2, after triggering the zero point button 4, the controller MCU3 reads the zero point value and polarity, and outputs a continuously increasing digital signal with opposite polarity, such as “0000 0001-0000 0010-0000 0011 ..." to the PWM generator 7. The PWM generator 7 converts the digital signal into a pulse signal with a gradually increasing duty cycle. After filtering, the pulse signal generates a continuously increasing voltage signal with opposite polarity and outputs it to the PWM generator 7. The differential amplifier circuit 2 makes the value output by the differential amplifier circuit 2 smaller until the zero point value read by the controller MCU3 is zero.

Example 2:

Referring to Figures 6 to 8, the present invention also includes a zero-point adjustment circuit for a digital DC clamp meter, including a Hall sensor 1, an operational amplifier 11, an integrated chip 12, a display LCD 5, a zero-point adjustment unit 13 and a zero button 4 ; The integrated chip 12 includes a controller MCU3, an A/D converter 121, a memory 122, an output unit 123, a keyboard processing unit 124 and an LCD driving unit 125. The A/D converter 121, the memory 122, and the output unit 123 The keyboard processing unit 124 and the LCD driving unit 125 are both electrically connected to the controller MCU 3; the two output terminals of the Hall sensor 1 are respectively connected to the forward input terminal and the reverse input terminal of the operational amplifier 11 via resistors R1 and R2. To the input end, the output end of the operational amplifier 11 is connected to the A/D converter 121 of the integrated chip 12, and the output end of the operational amplifier 11 is connected to the forward input end of the operational amplifier 11 through the resistor R3; so The output unit 123 is electrically connected to the inverting input end of the operational amplifier 11 via resistors R5 and R4, and the line between R4 and R5 is connected to the signal ground via resistor R6.

Further, a capacitor C1 is connected in parallel to both ends of the resistor R6, and the capacitor C1 is used for filtering.

The working principle of Embodiment 2 is as follows:

The operational amplifier 11 and the resistors R1, R2, R3 and R4 form a differential amplifier circuit. The Hall sensor 1 outputs the detected voltage to the two input terminals of the operational amplifier 11 for amplification, and the output terminal of the operational amplifier 11 outputs the amplified voltage. to the input end of the A/D converter 121 of the integrated chip 12. The A/D converter 121 converts the analog signal into a digital signal and then sends it to the controller MCU3. The controller MCU3 drives the LCD driving unit 125 according to the digital signal to drive the display screen. LCD5 displays the detected value;

Because there is an offset voltage between the Hall sensor 1 and the operational amplifier 11, when there is no detected object at the detection end, the operational amplifier 11 will still output a voltage to the integrated chip 12, causing a value to be displayed on the display screen LCD5. This value is Zero point value;

After triggering the zero adjustment button 4, the controller MCU3 identifies the size and polarity of the zero point value, and outputs a gradually increasing voltage with the opposite polarity to the zero point value through the output unit 123. The output voltage is divided by R5 and R4 and then output to the positive input terminal of the operational amplifier 11, so that the voltage values of the two input terminals of the operational amplifier 11 gradually approach to be equal, until the output voltage of the operational amplifier 11 is 0, the controller MCU3 records the voltage value output by the output unit 123, and continues to output this value. value, the zero point adjustment is completed.

The controller MCU3 controls the output unit 123 to send a continuously increasing voltage by sending a continuously increasing digital code, such as "0000 0001-00000010-0000 0011..." to the output unit 123. The output unit 123 can use a D/A converter or When the PWM generator outputs voltage through the D/A converter, after dividing the voltage by R5 and R4, the voltage changes from a ladder-shaped waveform to output a stable linear waveform; when the voltage is output through the PWM generator, the output voltage passes through After R6 and C1 are filtered, they are changed to output a stable linear waveform; making the output voltage more precise and precise.

The above are only examples of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description and drawings of the present invention, or directly or indirectly applied to other related technologies fields are equally included in the scope of patent protection of the present invention.

Claims (3)

1. A zero point adjusting method of a digital direct current clamp meter, wherein the digital direct current clamp meter comprises a zero point adjusting circuit, and the zero point adjusting circuit comprises: the device comprises a Hall sensor (1), an operational amplifier (11), an integrated chip (12), a display screen LCD (5), a zero point adjusting unit (13) and a zero point key (4); the operational amplifier (11) and the resistors R1, R2, R3 and R4 form a differential amplifying circuit (2); the integrated chip (12) comprises a controller MCU (3), an A/D converter (121), a memory (122), an output unit (123), a keyboard processing unit (124) and an LCD driving unit (125), wherein the A/D converter (121), the memory (122), the output unit (123), the keyboard processing unit (124) and the LCD driving unit (125) are electrically connected with the controller MCU (3); the two output ends of the Hall sensor (1) are respectively connected with the forward input end and the reverse input end of the operational amplifier (11) through resistors R1 and R2, the output end of the operational amplifier (11) is connected with the A/D converter (121) of the integrated chip (12), and the output end of the operational amplifier (11) is connected with the forward input end of the operational amplifier (11) through a resistor R3; the output unit (123) is electrically connected with the reverse input end of the operational amplifier (11) through resistors R5 and R4, and a circuit between the R4 and the R5 is connected with signal ground through a resistor R6; the two ends of the resistor R6 are connected in parallel with a capacitor C1; the zero point key (4) is connected with the controller MCU (3), the zero point adjusting unit (13) is arranged between the operational amplifier (11) and the integrated chip (12), and the display screen LCD (5) is connected with the controller MCU (3); the zero point adjusting method is characterized by comprising the following steps of:

step one, starting a digital direct current clamp meter to perform zero setting test, and pressing a zero point key (4) to perform zero setting when a display value of a display screen LCD (5) is not zero during no-load measurement;

after triggering the zero point key (4), the controller MCU (3) reads the zero point value and polarity, and outputs a signal which is continuously increased and has opposite polarity to the input end of the differential amplifying circuit (2), so that the value output by the differential amplifying circuit (2) is reduced until the zero point value read by the controller MCU (3) is zero;

and thirdly, when the zero point value is read to be zero, the controller MCU (3) records the output value at the moment, stores the output, stops the zeroing action and completes zeroing.

2. The zero point adjusting method of the digital direct current clamp meter according to claim 1, wherein the method comprises the following steps: in the second step, a D/a converter (6) is arranged in the output circuit of the controller MCU (3), after the zero point key (4) is triggered, the controller MCU (3) reads the zero point value and polarity, and outputs a digital signal with continuously increased polarity to the D/a converter (6), the D/a converter (6) converts the digital signal into a voltage signal with continuously increased polarity and opposite polarity, and outputs the voltage signal to the differential amplifying circuit (2), so that the value output by the differential amplifying circuit (2) becomes smaller until the zero point value read by the controller MCU (3) is zero.

3. The zero point adjusting method of the digital direct current clamp meter according to claim 1, wherein the method comprises the following steps: in the second step, a PWM generator (7) is arranged in the output circuit of the controller MCU (3), after the zero point key (4) is triggered, the controller MCU (3) reads the zero point value and polarity, and outputs a digital signal with continuously increased polarity to the PWM generator (7), the PWM generator (7) converts the digital signal into a pulse signal with gradually increased duty ratio, the pulse signal generates a voltage signal with continuously increased polarity and opposite polarity after filtering, and the voltage signal is output to the differential amplifying circuit (2), so that the value output by the differential amplifying circuit (2) becomes smaller until the zero point value read by the controller MCU (3) is zero.