CN212646965U

CN212646965U - Single-point calibration circuit structure realized by built-in resistance network of digital multimeter

Info

Publication number: CN212646965U
Application number: CN202020019496.8U
Authority: CN
Inventors: 严王军; 赵双龙
Original assignee: Hangzhou Sdic Microelectronics Co ltd
Current assignee: Hangzhou Jinghua Microelectronics Co.,Ltd.
Priority date: 2020-01-06
Filing date: 2020-01-06
Publication date: 2021-03-02
Anticipated expiration: 2030-01-06

Abstract

The utility model discloses a single-point calibration circuit structure that digital multimeter built-in resistance network realized, it includes: the device comprises an external signal input circuit, an internal resistance network circuit, a reference signal output circuit and a channel switching and ADC acquisition circuit. Firstly, the calibration of all resistance values of the internal resistance network can be realized by utilizing the specific connection configuration of the reference resistors (R5 and R6) and the internal resistance network without applying external signals; on the basis, voltage level measurement calibration can be realized only by externally inputting a direct current reference voltage. The utility model discloses circuit structure is showing and is simplifying outside auxiliary circuit and calibration flow, saves the device cost and improves volume production calibration efficiency.

Description

Single-point calibration circuit structure realized by built-in resistance network of digital multimeter

Technical Field

The utility model belongs to the technical field of the electronic technology and specifically relates to a single-point calibration circuit structure that digital multimeter embeds resistance network and realizes is related to.

Background

Digital multimeters are widely used in various large power electronic industries, belong to the technical field of electronic measurement, and must be calibrated in order to ensure the precision of a measuring instrument. The peripheral circuit that present ordinary digital multimeter designed is complicated, and the calibration needs the manual multimeter gear that waits to calibrate of operating personnel, and the manual interconnecting link of switching multimeter and calibration source according to the gear is at the manual input of calibration source end each calibration signal, carries out calibration data again and saves. The whole calibration process is complex, the workload is large, and errors are easy to occur when calibration points are manually input and signal measurement processing is carried out. And the digital multimeter can be difficult to avoid producing the error in the complicated design of its own hardware circuit, its main source of error is:

1. the precision of the resistor in the peripheral circuit of the chip is not high enough, and a certain temperature drift exists;

2. measuring errors generated by internal circuits of the chip;

3. noise and interference present in hardware circuits;

4. manual switching operation in different gears may have misoperation and the like.

Therefore, if errors existing in the design process of the digital multimeter are not processed and are provided for a customer to use, the measurement result deviation is large, the performance of the digital multimeter is directly influenced, and the measurement requirements of a user cannot be met. How to eliminate the error becomes a difficult point of digital versatile design. In addition to improving hardware circuitry, the most effective method of error elimination is to calibrate the digital multimeter. Calibration is one of the essential steps of an electronic measuring instrument from production to use. The purpose of this is to determine the indication of the measuring device by comparison with a standard. The accuracy and reliability of the measurement data can be guaranteed only by providing the measurement data to a user after calibration. With the development of digital multimeters and the pressure of industry competition, peripheral hardware circuits are increasingly required to be simple, convenient to calibrate and high in measurement accuracy.

SUMMERY OF THE UTILITY MODEL

The utility model aims at providing a single-point calibration circuit structure that digital multimeter built-in resistance network realized. The digital multimeter is designed to have a complex peripheral circuit, each gear is calibrated in a troublesome way, and the built-in resistance network realizes that a single-point calibration circuit structure overcomes the defects of complex peripheral circuit, troublesome calibration and the like of the traditional digital multimeter.

In order to achieve the above object, the present invention provides a circuit design comprising: the device comprises an external signal input circuit, an internal resistance network circuit, a reference signal output circuit and a channel switching and ADC acquisition circuit.

Preferably, the external signal input circuit comprises a high-precision low-temperature drift resistor R6, a PTC R5 for protection and an input port. Preferably, the resistance calibration connects the reference voltage COM (1.2V) generated by the chip to the A2 port through the switch K5, the A2 port to the PTC R5 for protection, the R5 to the high-precision low-temperature drift resistor R6, the R6 to the A1 port, and the A1 to the internal resistance network.

Preferably, the internal resistance network circuit comprises switches K1, K2, K3, K4 and resistors R1, R2, R3, R4. Preferably, the port A1 signal is connected to the resistor R4 through a K4 switch, the resistor R4 is connected with the resistors R3, R2 and R1 in sequence, and the R1 is connected with the switch K8 in resistance.

Preferably, the reference signal output circuit includes a switch K8, an operational amplifier OPA, K10, K9, and a MUX 1. Preferably, the switch K8 is connected to the output of the switch K10 to the OPA, the negative input of the OPA is fed back to the output, the positive input of the OPA is connected to K9, and the K9 is connected to the MUX1 selection reference voltage VDR20 (0.75V).

Preferably, the channel switching and ADC acquisition circuit includes a MUX2 and an ADC. Preferably, the voltage at the point VA selects V1P and V1N to collect the signal to the input of the ADC for storage by controlling the MUX 2. External high-precision low-temperature drift resistance signals are collected and stored from COM and VA to V1P to the input end of an ADC, and the actual resistance value of the internal resistance (R1+ R2+ R3+ R4) is obtained through two times of signal collection proportional conversion. The actual resistance value can be calculated by the same proportion measurement method for other internal resistors. Preferably, the voltage calibration can be realized by externally applying a direct current 100mV signal, collecting signals from the A2 and the COM to the input end of the ADC through the R5 port to the A2 port, calibrating through the mV step, measuring other voltage step signals from the R6 resistor to the A1 port to each resistor network, and testing all voltage signals to be tested through switching of the resistor networks.

Compared with the prior art, the utility model discloses there is following advantage, simplifies digital multimeter's peripheral circuit, only needs few components and parts just can realize measuring function such as resistance and voltage. The calibration is simple and convenient, and the measurement functions of resistance, voltage and the like can be realized by calibrating only one mV gear. The measurement precision is high, all measurement calculations are proportional measurements, and systematic errors, chip self-maladjustment and the like are counteracted. Reduce the production cost of manufacturers and improve the production efficiency.

Drawings

Fig. 1 is an embodiment structure diagram of a single-point calibration circuit structure implemented by the digital multimeter built-in resistor network provided by the present invention.

Detailed Description

For making the purpose, implementation and advantages of the present invention clearer, the drawings in the embodiments of the present invention will be combined below, to make the implementation shown in the drawings of the present invention clearer and more complete, the brief description needs to reach the purpose and have advantages in the implementation.

Preferably, the described embodiment is only one exemplary embodiment, and not all embodiments. The example components and described implementations of the present invention in the drawings may, however, be advantageously arranged and designed in a wide variety of different configurations. Accordingly, the embodiments of the invention provided in the drawings are not intended to limit the scope of the claimed invention, but are merely representative of preferred embodiments of the invention. Based on the embodiments described in the present disclosure, all other embodiments similar to this embodiment that other technicians in the field obtained on the premise of not deriving the creative work result all belong to the protection scope of the present invention.

Example (b):

referring to fig. 1, the working principle of the single-point calibration circuit structure implemented by the built-in resistance network of the digital multimeter is described with reference to fig. 1.

The chip internal resistor string is often named as R1, R2, R3 and R4 from small to large.

And order: res1 ═ R1; res2 ═ R1+ R2; res3 ═ R1+ R2+ R3; res4 ═ R1+ R2+ R3+ R4; the internal resistance is calibrated using an external high precision low temperature drift resistance R6. Firstly, a chip reference voltage COM (1.2V) is connected to A2, R5, R6, A1 and K4 connection resistor strings R4-R1-K8 connection operational amplifier output ends in sequence through K5 conduction, and the operational amplifier input ends select VDR20 (0.75V). The ADC collects voltage signals at two ends of R6 to store ADC code values, and the ADC switches a channel to collect signals of voltages at two ends of RES4 to store the ADC code values. The actual accurate value of RES4 is calculated as follows:

RES4 is then used to calibrate RES3, chip reference voltage COM (1.2V) is connected to K4 through K6, K4 is connected to resistor strings R4-R1-K8 and connected to the output end of the operational amplifier, and VDR20(0.75V) is selected as the input end of the operational amplifier. The ADC collects voltage signals at two ends of the RES4 to store ADC code values, and the ADC switches a channel to collect voltage signals at two ends of the RES3 to store the ADC code values. The actual accurate value of RES3 is calculated as follows:

similarly, RES3 is used for calibrating RES2, a chip reference voltage COM (1.2V) is connected with K3 through K6 in a conducting mode, K3 is connected to resistor strings R3-R1-K8 and connected with an operational amplifier output end, and VDR20(0.75V) is selected as the operational amplifier input end. The ADC collects voltage signals at two ends of the RES3 to store ADC code values, and the ADC switches a channel to collect voltage signals at two ends of the RES2 to store the ADC code values. The actual accurate value of RES2 is calculated as follows:

similarly, RES2 is used to calibrate RES1, chip reference voltage COM (1.2V) is connected to K2 through K6, K2 is connected to resistor string R2 and R1 to K8 are connected to the output end of the operational amplifier, and VDR20(0.75V) is selected as the input end of the operational amplifier. The ADC collects voltage signals at two ends of the RES2 to store ADC code values, and the ADC switches a channel to collect voltage signals at two ends of the RES1 to store the ADC code values. The actual accurate value of RES1 is calculated as follows:

after the internal resistance networks are calibrated, if different external resistances are measured, the principle is similar to the method in calibration, and the external actual resistance value is obtained by switching different resistance network proportions and calculating.

The voltage calibration only needs to be externally connected with a direct current 100mV signal to pass through R5 to A2, and the ADC acquires the signal between A2 and COM to obtain an ADC code value (ADC)_Calibration). Measuring mV (V)_x) The signals may be according to the following companies:

other voltage levels are measured and obtained through calculation of an internal resistance network, the internal resistances used by different voltage levels are different, for example, 2V level is obtained through proportion calculation of signals through R6 resistance and internal RES4 voltage division, other levels are the same, and the measurement of alternating current signals is the same, and the method can be specifically obtained according to the following formula:

the embodiment of the utility model provides an in, the principle of carrying out the single-point calibration to digital multimeter has been realized to the inside resistance network of chip having utilized ingeniously to peripheral circuit is simple, and the calibration is simple and convenient, and the interference killing feature is strong, and measurement accuracy and measurement reliability improve (all measures all are the error that the system exists is offset in the ratio measurement). Meanwhile, the production cost of manufacturers is reduced and the production efficiency is improved.

Claims

1. The utility model provides a single-point calibration circuit structure that digital multimeter built-in resistance network realized which characterized in that includes: the circuit comprises an external signal input circuit, an internal resistance network circuit, a reference signal output circuit and a channel switching and ADC (analog to digital converter) acquisition circuit, wherein the external signal input circuit comprises a high-precision low-temperature drift resistor R6, a port A1, a PTC resistor R5 for protection and an input port A2; the internal resistance network circuit comprises resistors R1, R2, R3 and R4 and switches K1, K2, K3 and K4; the reference signal output circuit comprises an operational amplifier (OPA), switches K8, K9, K10 and a channel switching MUX 1; the channel switching and ADC acquisition circuit comprises a channel switching MUX2 and an analog-to-digital converter ADC.

2. The single-point calibration circuit structure realized by the built-in resistor network of the digital multimeter as claimed in claim 1, wherein the reference voltage COM generated by the chip is connected to the port A2 through a switch K5, the port A2 is connected to one end of a resistor R5, the other end of the resistor R5 is connected to one end of a resistor R6, the other end of the resistor R6 is connected to the port A1, and the other end of the resistor A1 is connected to the internal resistor network.

3. The single-point calibration circuit structure realized by the built-in resistor network of the digital multimeter as claimed in claim 1, wherein one end of A1 is connected to a resistor R4 through a switch K4, the resistor R4 is connected to resistors R3, R2 and R1 in sequence, and the resistor R1 is connected to the switch K8.

4. The single-point calibration circuit structure realized by the built-in resistor network of the digital multimeter as claimed in claim 1, wherein the switch K8 is connected with the switch K10, and the other end of the switch K10 is connected with the output end OPOUT of the OPA; the negative input end of the operational amplifier OPA is connected to the common end of the switch K10 and the switch K8, the positive input end of the operational amplifier OPA is connected to the OPIN and connected to the switch K9, and the other end of the switch K9 is connected to the output end of the channel switching MUX 1.

5. The single-point calibration circuit structure realized by the built-in resistor network of the digital multimeter as claimed in claim 1, wherein the switch K4 and the common terminal VA of the resistor R4, the common terminal VB of the resistor R3 and the resistor R4, the common terminal VC of the resistor R2 and the resistor R3, the common terminal VD of the resistor R1 and the resistor R2 are connected with the input terminal of the channel switching MUX2, and the output terminal V1P of the channel switching MUX2 is connected to the first input terminal of the ADC;

the resistor R1 and the common end V1N of the switch K8 are connected with the fifth input end of the ADC;

the second input of the ADC is connected to port a1, the third input of the ADC is connected to port a2, and the fourth input of the ADC is connected to port COM.