CN108196115A - A kind of zero point adjusting method and circuit of digital direct current pincerlike meter - Google Patents

Abstract

The invention relates to a zero point adjustment method of 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 screen LCD; the zero point adjustment method 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-adjustment button to perform zero-adjustment; Step 2. After triggering the zero-adjustment button , the controller MCU reads the zero point value and polarity, and outputs a continuously increasing signal with opposite polarity to the input terminal of the differential amplifier circuit, so that the value output by the differential amplifier circuit becomes smaller until the zero point read by the controller MCU The value is zero; step 3, when the read zero value is 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.

Description

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

technical field

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

Background technique

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

Therefore, all digital DC clamp meters using Hall sensors need a method and circuit for processing the measurement zero point; however, there are two traditional zero adjustment methods:

One is to use the 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 supply, and the slideway end obtains a certain voltage. After the voltage is divided by R5\R6, the difference is input through R4. Amplifier A adjusts the Vo value. Since positive and negative voltages can be obtained at the slideway end, adjust Vo to be 0. Figure 1 Use the 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 and the zero point shifts, resulting in reading errors and troublesome use; 2. The Hall device The consistency is poor, and the zero point adjustment range needs to maintain a certain range. During production, it must be pre-adjusted inside the instrument according to different Halls. Mass production is not easy and the efficiency is low.

The other is to use the software zero adjustment method, as shown in Figure 2, which is to use the software zero adjustment method. The MCU directly reads and saves the zero point value, and uses the MCU’s computing function to directly deduct the zero point from the reading of the measured amplifier output value. The value is the voltage value, and this method of relative value measurement is simple. However, with the method of relative value measurement, since the input of zero point voltage sometimes seriously affects the measurement range of MCU, 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, which is not easily affected by the operation of the instrument. Therefore, the hardware circuit still has the operation of pre-correcting 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 and the value is 20mV, the maximum voltage converted by the instrument to measure voltage is only 380mV. Make the measuring range of the instrument smaller.

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, which overcomes the shortcomings of the zero point adjustment of the traditional digital DC clamp meter in use and production, Adjustment with potentiometers is not required and does not affect the measuring range.

Technical scheme of the present invention is as follows:

Technical solution one:

A zero point adjustment method of a digital DC clamp meter, the digital DC clamp meter includes a Hall sensor, a differential amplifier circuit, a controller MCU, a zero button and a display screen LCD; the Hall sensor generates a measurement voltage and Input to the input terminal of the differential amplifier circuit, the output terminal 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 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 terminal of the differential amplifier circuit, so that the output value of the differential amplifier circuit becomes smaller until The zero value read by the controller MCU is zero;

Step 3. When the read zero value is 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 2, a D/A converter is provided in the output circuit of the controller MCU. 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, and 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, so that the value output by the differential amplifier circuit becomes smaller , until the zero value read by the controller MCU is zero.

Alternatively, in step 2, the output circuit of the controller MCU is provided with a PWM generator, and after the zero button is triggered, the controller MCU reads the zero value and polarity, and outputs a continuously increasing, opposite polarity The digital signal of the digital signal is sent to the PWM generator, and the PWM generator converts the digital signal into a pulse signal with a gradually increasing duty ratio. After the pulse signal is filtered, a continuously increasing voltage signal with opposite polarity is output to the differential amplifier. The circuit makes the value output by the differential amplifier circuit smaller until the zero value read by the controller MCU is zero.

Technical solution two:

The present 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 drive unit, the A/D converter, memory, output unit, keyboard processing unit and LCD drive unit are all electrically connected to the controller MCU; The two output terminals of the Hall sensor are respectively connected to the positive 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 with the positive input terminal of the operational amplifier through the resistor R3; the output unit is electrically connected with the negative input terminal of the operational amplifier through the resistors R5 and R4, and the connection between the R4 and R5 The line is connected to the signal ground through the resistor R6.

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

The present invention has following beneficial effects:

1. There is no potentiometer in the circuit, and there is no need to adjust the parameters of the zero return circuit;

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 voltage of the zeroing signal to make the zeroing more precise and accurate;

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

Description of drawings

Fig. 1 is the implementation circuit diagram of the first scheme in the prior art;

Fig. 2 is the implementation circuit diagram of the second scheme in the prior art;

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

Figure 4 is a functional block diagram of the D/A converter solution;

Fig. 5 is a functional block diagram of a scheme using a PWM generator;

Fig. 6 is the functional block diagram of embodiment two;

Figure 7 is a voltage waveform using a D/A converter;

Figure 8 shows the voltage waveform using a PWM generator.

The reference signs in the figure represent:

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 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 in conjunction with the accompanying drawings and specific embodiments.

Embodiment one:

Referring to Fig. 3 to Fig. 5, a zero adjustment method of a digital DC clamp meter, the digital DC clamp meter includes a Hall sensor 1, a differential amplifier circuit 2, a controller MCU3, a zero button 4 and a display screen LCD5 The Hall sensor 1 generates a measurement voltage and is input to the input terminal of the differential amplifier circuit 2, the output terminal 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 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 terminal of the differential amplifier circuit 2, so that the value output by the differential amplifier circuit 2 becomes Small, until the zero value read by the controller MCU3 is zero;

Step 3. When the read zero value is 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 2, the output circuit of the controller MCU3 is provided with a D/A converter 6, after the zero button 4 is triggered, the controller MCU3 reads the zero value and polarity, and outputs a continuously increasing, A 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 value read by the controller MCU3 is zero.

Alternatively, in step 2, after the zero point button 4 is triggered, 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, and the pulse signal is filtered to generate a continuously increasing voltage signal with opposite polarity and output to the The differential amplifier circuit 2 makes the value output by the differential amplifier circuit 2 smaller until the zero value read by the controller MCU3 is zero.

Embodiment two:

Referring to Fig. 6 to Fig. 8, the present invention also includes a zero point adjustment circuit of a digital DC clamp meter, including a Hall sensor 1, an operational amplifier 11, an integrated chip 12, a display screen LCD5, a zero point adjustment unit 13 and a zero point button 4 Described integrated chip 12 comprises controller MCU3, A/D converter 121, memory 122, output unit 123, keyboard processing unit 124 and LCD drive unit 125, described A/D converter 121, memory 122, output unit 123 , the keyboard processing unit 124 and the LCD drive unit 125 are all electrically connected to the controller MCU3; the two output terminals of the Hall sensor 1 are respectively connected to the positive input terminal and the negative input terminal of the operational amplifier 11 via resistors R1 and R2. To the input terminal, the output terminal of the operational amplifier 11 is connected to the A/D converter 121 of the integrated chip 12, and the output terminal of the operational amplifier 11 is connected with the positive input terminal of the operational amplifier 11 through a resistor R3; The output unit 123 is electrically connected to the inverting input terminal of the operational amplifier 11 through resistors R5 and R4, and the line between R4 and R5 is connected to signal ground through a resistor R6.

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

The working principle of embodiment two 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 sends it to the controller MCU3, and the controller MCU3 drives the LCD drive 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 object to be detected at the detection terminal, the operational amplifier 11 will still output a voltage to the integrated chip 12, so that a value is displayed on the display screen LCD5, which is zero value;

After triggering the zero adjustment button 4, the controller MCU3 recognizes the magnitude and polarity of the zero point value, and outputs a gradually increasing voltage with opposite polarity to the zero point value through the output unit 123, and the output voltage is divided by R5 and R4 to 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 are gradually approached 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 continuously outputs this Numerical value, adjust the zero point to complete.

The controller MCU3 sends continuously increasing digital codes to the output unit 123, such as "0000 0001-00000010-0000 0011..." to control the output unit 123 to send continuously increasing voltages. The output unit 123 can use a D/A converter or PWM generator, when the voltage is output through the D/A converter, after the voltage is divided by R5 and R4, the voltage changes from a ladder-shaped waveform to a stable linear waveform; when the voltage is output through the PWM generator, the output voltage passes through After filtering by R6 and C1, it is changed to output a stable linear waveform; making the output voltage more precise and accurate.

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technologies fields, all of which are equally included in the scope of patent protection of the present invention.

Claims (5)

1. a kind of zero point adjusting method of digital direct current pincerlike meter, the digital direct current pincerlike meter includes Hall sensor （1）, differential amplifier circuit（2）, controller MCU（3）, zero button（4）With display screen LCD（5）；The Hall sensor（1） It generates measurement voltage and is input to the differential amplifier circuit（2）Input terminal, the differential amplifier circuit（2）Output terminal connect Meet the controller MCU（3）, the zero button（4）Connect the controller MCU（3）, the display screen LCD（5）Connection institute State controller MCU（3）；It is characterized in that, the zero point adjusting method includes the following steps：

Step 1: starting digital direct current pincerlike meter carries out zeroing test, as display screen LCD（5）The show value when zero load measures When being not zero, zero button is pressed（4）It returns to zero；

Step 2: triggering zero button（4）Afterwards, controller MCU（3）Zero numerical value and polarity are read, and exports a lasting increasing Greatly, opposite polarity signal is to differential amplifier circuit（2）Input terminal, make differential amplifier circuit（2）The numerical value of output becomes smaller, directly To controller MCU（3）The zero numerical value of reading is zero；

Step 3: when it is zero to read zero numerical value, controller MCU（3）It records output numerical value at this time and preserves output, stop Only zeroing acts, and completes zeroing.

2. a kind of zero point adjusting method of digital direct current pincerlike meter according to claim 1, it is characterised in that：In step In two, the controller MCU（3）Output circuit in be equipped with D/A converter（6）, trigger zero button（4）Afterwards, controller MCU （3）Zero numerical value and polarity are read, and exports lasting increase, an opposite polarity digital signal to the D/A converter （6）, D/A converter（6）Convert digital signals into lasting increase, opposite polarity voltage signal is exported to the differential amplification Circuit（2）, make differential amplifier circuit（2）The numerical value of output becomes smaller, until controller MCU（3）The zero numerical value of reading is zero.

3. a kind of zero point adjusting method of digital direct current pincerlike meter according to claim 1, it is characterised in that：In step In two, the controller MCU（3）Output circuit in be equipped with PWM generator（7）, trigger zero button（4）Afterwards, controller MCU （3）Zero numerical value and polarity are read, and exports lasting increase, an opposite polarity digital signal to the PWM generator （7）, PWM generator（7）Duty ratio gradually increased pulse signal is converted digital signals into, is generated after pulse signal is filtered Lasting increase, opposite polarity voltage signal are exported to the differential amplifier circuit（2）, make differential amplifier circuit（2）Output Numerical value becomes smaller, until controller MCU（3）The zero numerical value of reading is zero.

4. a kind of zero adjustment circuit of digital direct current pincerlike meter, it is characterised in that：Including Hall sensor（1）, operation puts Big device（11）, integrated chip（12）, display screen LCD（5）, zero adjust unit（13）With zero button（4）；The integrated chip （12）Including controller MCU（3）, A/D converter（121）, memory（122）, output unit（123）, Data inputing unit （124）With LCD driving units（125）, the A/D converter（121）, memory（122）, output unit（123）, Data inputing Unit（124）With LCD driving units（125）With the controller MCU（3）Electrical connection；The Hall sensor（1）It is two defeated Outlet is connected to the operational amplifier through resistance R1 and R2 respectively（11）Positive input and reverse input end, the operation puts Big device（11）Output be terminated at the integrated chip（12）A/D converter（121）, the operational amplifier（11）Output End is through resistance R3 and operational amplifier（11）Positive input connection；The output unit（123）Through resistance R5 and R4 and institute State operational amplifier（11）Reverse input end electrical connection, the circuit between the R4 and R5 is connected to signal ground through resistance R6.

5. a kind of zero adjustment circuit of digital direct current pincerlike meter according to claim 4, it is characterised in that：The electricity Hinder one capacitance C1 of R6 both ends parallel connections.