Self-checking device for the input impedance of an instrument

Abstract

The present application belongs to the technical field of instruments and meters, and particularly relates to a self-checking device for input impedance of an instrument, which is applied to a measuring instrument, and the measuring instrument has a meter pen input end and comprises: an input protection module having a first protection branch, a second protection branch and a third protection branch connected in parallel; a conduction control module connected with the first protection branch through an impedance module, and the conduction control module is connected with the second protection branch and the third protection branch respectively; one end of a safe input detection module is connected with the conduction control module; a first end and a second end of a measurement network selection module are connected with the conduction control module respectively; and a measurement calculation module is connected with the measurement network selection module and the installation input detection module respectively. Before voltage measurement, the instrument needs to pass through impedance self-checking first, and then measurement can be performed, so as to improve the measurement safety of the instrument and improve the use convenience of the instrument.

Description

Technical Field

[0001] This application relates to the field of instrumentation technology, and in particular to a self-testing device for the input impedance of an instrument. Background Technology

[0002] Since the input impedance of an instrument has a significant impact on measurement accuracy and safety, it is necessary for measurement personnel to know the input impedance of the instrument in advance and confirm whether this impedance value is suitable for the current measurement.

[0003] When measuring voltage, if the input impedance of the measuring instrument is too low, the following effects will occur: First, when the input impedance of the instrument is 1% of the impedance of the signal source being measured, a measurement error of about 1% will occur, and the smaller the input impedance of the instrument, the greater the error will be. Second, if the input impedance of the instrument is too low, it may cause the protective switch to trip when measuring voltage. For example, when measuring the voltage between the live wire and the ground wire, if the input impedance of the instrument is too low, it will cause the current from the live wire to the ground wire to be too large, which will cause the leakage current switch to trip. Third, if the input impedance of the instrument is too low, it may damage the instrument when measuring high voltage, which may lead to serious safety accidents.

[0004] In related technologies, multimeters do not have the function of self-testing the input impedance of the instrument itself. Users can only obtain the information of the instrument's input impedance from the instruction manual, which is very inconvenient.

[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] In view of at least one of the above technical problems, this application provides a self-testing device for the input impedance of an instrument, which solves the problem that multimeters do not have the function of self-testing the input impedance of the instrument itself, and users can only obtain the information of the instrument's input impedance from the instruction manual, which is very inconvenient.

[0007] This application provides a self-testing device for the input impedance of an instrument, which is applied to a measuring instrument. The measuring instrument has a probe input terminal and includes an input protection module, an impedance module, a continuity control module, a safety input detection module, a measurement network selection module, and a measurement calculation module.

[0008] The input protection module has a first protection branch, a second protection branch, and a third protection branch connected in parallel;

[0009] A conduction control module is connected to the first protection branch through an impedance module, and the conduction module is connected to the second protection branch and the third protection branch respectively.

[0010] A safety input detection module, one end of which is connected to the conduction control module;

[0011] A measurement network selection module, the first and second ends of which are respectively connected to a conduction control module;

[0012] The measurement calculation module is connected to the measurement network selection module and the installation input detection module.

[0013] This application has the following technical effects: This self-testing device, through the cooperation of an input protection module, an impedance module, a continuity control module, a safety input detection module, a measurement network selection module, and a measurement calculation module, requires the instrument to undergo an impedance self-test before voltage measurement can be performed, thereby improving the measurement safety and ease of use of the instrument.

[0014] In one implementation, the first protection branch includes a first protection unit, the second protection branch includes a second protection unit, and the third protection branch includes a third protection unit, with the first protection unit, the second protection unit, and the third protection unit connected in parallel.

[0015] In one implementation, the impedance module includes a first resistor, a fourth resistor, a fifth resistor, and a sixth resistor connected in series. The first resistor is connected to the first protection unit, and the sixth resistor is connected to the conduction control module.

[0016] In one implementation, the conduction control module includes a first control switch, a second control switch, a third control switch, a fourth control switch, and a fifth control switch controlled by the measurement calculation module. Each of the first, second, third, fourth, and fifth control switches has a first contact terminal and a third contact terminal. The first control switch is connected between the second protection unit and the measurement network selection module. The second and third control switches are connected in sequence. The second control switch is connected to the third protection unit. The third control switch is connected to the safety input detection module. The fourth and fifth control switches are connected in sequence. The fourth control switch is connected to the sixth resistor. The fifth control switch is connected to the measurement network selection module.

[0017] In one implementation, when the measuring instrument is in a safe input detection state, the first control switch, the third control switch, the fourth control switch, and the fifth control switch are all placed at the first contact terminal, and the second control switch is placed at the third contact terminal.

[0018] In one implementation, when the measuring instrument is in the non-impedance branch self-test state, the first control switch, the second control switch, and the third control switch are all placed at the third contact terminal, and the fourth control switch is placed at the first contact terminal.

[0019] In one implementation, when the measuring instrument is in the input impedance self-test state, the second, third, fourth, and fifth control switches are all placed at the third contact terminal, and the first control switch is placed at the first contact terminal.

[0020] In one implementation, the safety input detection module includes a fifth varistor, a seventh resistor, an eighth resistor, and a voltage comparator. The fifth varistor is connected to the conduction control module. The first end of the seventh resistor is connected to the fifth varistor. The second end of the seventh resistor and the first end of the eighth resistor are connected together and connected to the non-inverting input of the voltage comparator. The inverting input of the voltage comparator is connected to the second power supply. The output of the voltage comparator is connected to the measurement and calculation module.

[0021] In one implementation, the measurement calculation module includes an ADC and an MCU. The ADC is used to receive the signal to be measured sent by the measurement network selection module and send it to the MCU for calculation.

[0022] In one implementation, the measurement network selection module includes a data selector, with the first and second ends of the data selector connected to the conduction control module, and the third end of the data selector connected to the measurement calculation module.

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a structural diagram of the self-testing device in the embodiments of this application;

[0026] Figure 2 This is a circuit diagram of the self-testing device in the embodiments of this application;

[0027] Figure 3 This is a circuit diagram of the self-testing device in the safe testing state in the embodiments of this application;

[0028] Figure 4 This is a circuit diagram of the self-test device in the non-impedance branch self-test state in the embodiments of this application;

[0029] Figure 5 This is a circuit diagram of the self-testing device in the input impedance self-testing state in the embodiments of this application;

[0030] Figure 6 This is a schematic diagram of the working principle of the self-testing device in the embodiments of this application; Detailed Implementation

[0031] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0032] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0033] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0034] In the embodiments of this application, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0035] When measuring voltage, if the input impedance of the measuring instrument is too low, the following effects will occur: First, when the instrument's input impedance is 1% of the impedance of the signal source being measured, an error of approximately 1% will occur; the lower the input impedance, the greater the error. Second, excessively low input impedance may cause the protective switch to trip when measuring voltage. For example, when measuring the voltage between the live wire and ground wire, if the instrument's input impedance is too low, the current from the live wire to the ground wire will be too large, causing the leakage current switch to trip. Third, excessively low input impedance may damage the instrument when measuring high voltage, potentially leading to serious safety accidents. Currently, multimeters do not have a function to self-test the instrument's input impedance; users can only obtain this information from the instruction manual, which is very inconvenient. This self-testing device, through the cooperation of an input protection module, impedance module, conduction control module, safety input detection module, measurement network selection module, and measurement calculation module, requires the instrument to undergo an impedance self-test before voltage measurement, thereby improving the measurement safety and ease of use of the instrument.

[0036] Please see Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 ,in, Figure 1 This is a structural diagram of the self-testing device in the embodiments of this application; Figure 2 This is a circuit diagram of the self-testing device in the embodiments of this application; Figure 3 This is a circuit diagram of the self-testing device in the safe testing state in the embodiments of this application; Figure 4 This is a circuit diagram of the self-test device in the non-impedance branch self-test state in the embodiments of this application; Figure 5 This is a circuit diagram of the self-testing device in the input impedance self-testing state in the embodiments of this application; Figure 6 This is a schematic diagram of the working principle of the self-testing device in the embodiment of this application; the embodiment of this application provides a self-testing device for the input impedance of an instrument, which is applied to a measuring instrument. The measuring instrument has a probe input terminal J1 and includes an input protection module 100, an impedance module 200, a conduction control module 300, a safety input detection module 400, a measurement network selection module 500, and a measurement calculation module 600.

[0037] Reference Figure 1 , Figure 2 and Figure 6 The following is a detailed introduction to the specific circuit structure and principle of the self-testing device.

[0038] The input protection module 100 has a first protection branch, a second protection branch, and a third protection branch connected in parallel;

[0039] A conduction control module 300 is connected to the first protection branch through an impedance module 200, and the conduction module is connected to the second protection branch and the third protection branch respectively.

[0040] A safety input detection module 400, one end of which is connected to the conduction control module 300;

[0041] A measurement network selection module 500, the first end of which is connected to the conduction control module 300, and the second end of which are respectively connected to the measurement network selection module 500.

[0042] The measurement calculation module 600 is connected to the measurement network selection module 500 and the installation input detection module.

[0043] In some examples, in conjunction with references Figure 1 , Figure 2 and Figure 6 The first protection branch includes a first protection unit, the second protection branch includes a second protection unit, and the third protection branch includes a third protection unit. The first protection unit, the second protection unit, and the third protection unit are connected in parallel.

[0044] The first protection branch also includes a fourth varistor DT4, the second protection resistor also includes a second varistor DT2, and the third protection resistor also includes a first varistor DT1. The first protection unit is a first thermistor PTC1, the second protection unit is a second thermistor PTC2, and the third protection unit is a third thermistor PTC3.

[0045] In this configuration, one end of the first thermistor PTC1, the second thermistor PTC2, and the third thermistor PTC3 are connected together. The other end of the first thermistor PTC1 is connected to the fourth varistor DT4. The other end of the second thermistor PTC2 is connected to the second varistor DT2. The other end of the third thermistor PTC3 is connected to the first varistor DT1. The first varistor DT1, the second varistor DT2, and the fourth varistor DT4 are grounded through the third varistor DT3. Thus, the first thermistor PTC1, the second thermistor PTC2, the third thermistor PTC3, the first varistor DT1, the second varistor DT2, the fourth varistor DT4, and the third varistor DT3 work together to provide surge protection for the probe input terminal J1 of the measuring instrument.

[0046] In some examples, in conjunction with references Figure 1 , Figure 2 and Figure 6The impedance module 200 includes a first resistor R1, a fourth resistor R4, a fifth resistor R5, and a sixth resistor R6 connected in series. The first resistor R1 is connected to the first protection unit, and the sixth resistor R6 is connected to the conduction control module 300.

[0047] In some examples, in conjunction with references Figure 1 , Figure 2 and Figure 6 The conduction control module 300 includes a first control switch K1, a second control switch K2, a third control switch K3, a fourth control switch K4, and a fifth control switch K5 controlled by the measurement calculation module 600. Each of the first control switch K1, second control switch K2, third control switch K3, fourth control switch K4, and fifth control switch K5 has a first contact end and a third contact end. The first control switch K1 is connected between the second protection unit and the measurement network selection module 500. The second control switch K2 and the third control switch K3 are connected in sequence. The second control switch K2 is connected to the third protection unit, and the third control switch K3 is connected to the safety input detection module 400. The fourth control switch K4 and the fifth control switch K5 are connected in sequence. The fourth control switch K4 is connected to the sixth resistor R6, and the fifth control switch K5 is connected to the measurement network selection module 500.

[0048] In some examples, in conjunction with references Figure 1 , Figure 2 and Figure 6 The measurement calculation module 600 includes an ADC and an MCU. The ADC is used to receive the signal to be measured sent by the measurement network selection module 500 and send it to the MCU for calculation.

[0049] In some examples, in conjunction with references Figure 1 , Figure 2 and Figure 6 The measurement network selection module 500 includes a data selector. The first and second ends of the data selector are connected to the conduction control module 300, and the third end of the data selector is connected to the measurement calculation module 600.

[0050] The measurement network selection module 500 also includes a first node a, a second node b, a third node c, a ninth resistor R9, a tenth resistor R10, and a first power supply V1. The first end of the ninth resistor R9 is connected to the first node a, and the second end of the ninth resistor R9 is connected to the second node b. The first node a is connected to the third contact terminal of the fifth control switch K5 and the first end of the data selector. The first end of the tenth resistor R10 is connected to the third node c, and the second end of the tenth resistor R10 is connected to the second node b. The third node c is connected to the second end of the data selector. The first power supply V1 is connected to the second node b.

[0051] In some examples, in conjunction with references Figure 3 When the measuring instrument is in the safe input detection state, the first control switch K1, the third control switch K3, the fourth control switch K4 and the fifth control switch K5 are all placed at the first contact end, and the second control switch K2 is placed at the third contact end.

[0052] The safety input detection module 400 includes a fifth varistor DT5, a seventh resistor R7, an eighth resistor R8, and a voltage comparator U1. The fifth varistor DT5 is connected to the conduction control module 300. The first end of the seventh resistor R7 is connected to the fifth varistor DT5. The second end of the seventh resistor R7 and the first end of the eighth resistor R8 are connected together and connected to the non-inverting input of the voltage comparator U1. The inverting input of the voltage comparator U1 is connected to the second power supply. The output of the voltage comparator U1 is connected to the measurement calculation module 600.

[0053] The fifth varistor DT5 is turned on when the measured voltage is greater than 180V. A third resistor R3 is also connected between the third thermistor PTC3 and the second control switch K2.

[0054] Before the instrument performs voltage measurement, it first checks the voltage input status. Specifically, the MCU controls the first control switch K1, the third control switch K3, the fourth control switch K4, and the fifth control switch K5 to be at their first contact terminals, and controls the second control switch K2 to be at its third contact terminal. At this time, if there is a voltage input higher than 180V at the meter input terminal J1, the fifth varistor DT5 conducts, allowing the measured voltage to pass through the circuit formed by the third thermistor PTC3, the third resistor R3, the fifth varistor DT5, the seventh resistor R7, and the eighth resistor R8. The eighth resistor R8 is a sampling resistor, and the sampled voltage on R8 is input to the voltage comparator U1, causing the voltage comparator U1 to output a high level to the MCU. In this way, the MCU can determine whether there is a high voltage input at the meter input terminal J1, effectively judging the magnitude of the measured voltage and preventing excessively high measured voltages from damaging the instrument.

[0055] In some examples, in conjunction with references Figure 4 When the measuring instrument is in the non-impedance branch self-test state, the first control switch K1, the second control switch K2, and the third control switch K3 are all placed at the third contact terminal, and the fourth control switch K4 is placed at the first contact terminal.

[0056] A second resistor R2 is connected between the second thermistor PTC2 and the first control switch K1.

[0057] When the self-test device is in the safe input detection state, the voltage comparator U1 does not output a high level to the MCU. Therefore, the self-test device enters the non-impedance branch self-test state. When the self-test device is in the non-impedance branch self-test state, the MCU controls the first control switch K1, the second control switch K2, and the third control switch K3 to be placed at the third contact terminal, and the fourth control switch K4 to be placed at the first contact terminal. At this time, the first power supply V1 outputs the first voltage, which is then transmitted through a circuit consisting of the tenth resistor R10, the second resistor R2, the second thermistor PTC2, the third thermistor PTC3, and the third resistor R3. The aforementioned ADC reads the voltages at the second node b and the third node c through the data selector. Specifically, the second resistor R2, the second thermistor PTC2, the third thermistor PTC3, and the third resistor R3 are connected in series to divide the voltages Vc and Vb. Therefore, the voltage across the tenth resistor R10 is Vc. R10 =V b -V c The MCU uses the formula Rf = V c ×R10÷V R10 The input impedance of the non-impedance branch is calculated.

[0058] In some examples, in conjunction with references Figure 5 When the measuring instrument is in the input impedance self-test state, the second control switch K2, the third control switch K3, the fourth control switch K4 and the fifth control switch K5 are all placed at the third contact terminal, and the first control switch K1 is placed at the first contact terminal.

[0059] When the self-test device is in the non-impedance branch self-test state, and the input impedance of the non-impedance branch is within the design range, the self-test device enters the input impedance self-test state. When the self-test device is in the input impedance self-test state, the MCU controls the second control switch K2, the third control switch K3, the fourth control switch K4, and the fifth control switch K5 to be placed at the third contact terminal, and controls the first control switch K1 to be placed at the first contact terminal. At this time, the first voltage output by the first power supply V1 passes through the circuit formed by the ninth resistor R9, the sixth resistor R6, the fifth resistor R5, the fourth resistor R4, the first resistor R1, the first thermistor PTC1, the third thermistor PTC3, and the third resistor R3. The ADC reads the voltages at the first node a and the second node b through the data selector. Specifically, the sixth resistor R6, the fifth resistor R5, the fourth resistor R4, the first resistor R1, the first thermistor PTC1, the third thermistor PTC3, and the third resistor R3 are connected in series to divide the voltage Va and Vb. Therefore, the voltage on the ninth resistor R9 is V. R9 =V b -V a The MCU uses the formula Rin = V a ×R9÷V R9 The input impedance Rin of the instrument voltage measurement is calculated.

[0060] When the input impedance Rin of the voltage measurement instrument is within the design range, the measuring instrument enters the voltage measurement state. The MCU controls the first control switch K1, the second control switch K2, the third control switch K3, and the fifth control switch K5 to be placed at the first contact terminal, and the fourth control switch K4 to be placed at the third contact terminal. The voltage to be measured is input from the probe input terminal J1, and after surge protection by the input protection module 100, it passes through the series connection of the first resistor R1, the fourth resistor R4, the fifth resistor R5, and the sixth resistor R6, and is then divided by the eleventh resistor. The ADC measures the voltage across the eleventh resistor, and the result is expressed by the formula V. in =V R11 Calculate the measured voltage by multiplying (R1+R4+R5+R6+R11) by R11.

[0061] Reference Figure 6 When the instrument is set to the voltage measurement range, the first control switch K1, the second control switch K2, the third control switch K3, the fourth control switch K4, and the fifth control switch K5 are all placed at their first contact terminals, disconnecting all input branches. Then, the MCU controls the instrument to enter a safety input detection state. If a high-voltage input is detected, the instrument issues a warning and does not proceed to the next step. If no high-voltage input is detected, the instrument enters a non-impedance branch self-test state. If the resistance of the non-impedance branch is outside the design range, the instrument issues a warning and does not proceed to the next step. If the resistance of the non-impedance branch is within the design range, the instrument enters an input impedance self-test state and displays the detected input impedance value Rin on the display screen. If the input impedance is outside the design range, the instrument issues a warning. If the input impedance is within the design range, it exits the self-test state after 2 seconds and enters the normal measurement state.

[0062] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The above are merely preferred embodiments of this application and do not constitute any limitation on this application. Any person skilled in the art can make many possible variations and modifications to the technical solution of this application, or modify it into equivalent embodiments, without departing from the scope of the technical solution of this application. Therefore, all equivalent changes made based on the shape, structure, and principle of this application without departing from the content of the technical solution of this application should be covered within the protection scope of this application.

Claims

1. A self-testing device for the input impedance of an instrument, applied to a measuring instrument, the measuring instrument having a probe input terminal, characterized in that, It includes an input protection module, an impedance module, a conduction control module, a safety input detection module, a measurement network selection module, and a measurement calculation module; The input protection module has a first protection branch, a second protection branch, and a third protection branch connected in parallel; The conduction control module is connected to the first protection branch through the impedance module, and is also connected to the second protection branch and the third protection branch respectively. The security input detection module, one end of which is connected to the conduction control module; The measurement network selection module has its first and second ends connected to the conduction control module, respectively. The measurement calculation module is connected to the measurement network selection module and the installation input detection module respectively; The first protection branch includes a first protection unit, the second protection branch includes a second protection unit, and the third protection branch includes a third protection unit. The first protection unit, the second protection unit, and the third protection unit are connected in parallel. The impedance module includes a first resistor, a fourth resistor, a fifth resistor, and a sixth resistor connected in series. The first resistor is connected to the first protection unit, and the sixth resistor is connected to the conduction control module. The conduction control module includes a first control switch, a second control switch, a third control switch, a fourth control switch, and a fifth control switch controlled by the measurement calculation module. Each of the first, second, third, fourth, and fifth control switches has a first contact terminal and a third contact terminal. The first control switch is connected between the second protection unit and the measurement network selection module. The second and third control switches are connected in sequence. The second control switch is connected to the third protection unit. The third control switch is connected to the safety input detection module. The fourth and fifth control switches are connected in sequence. The fourth control switch is connected to a sixth resistor. The fifth control switch is connected to the measurement network selection module. The safety input detection module includes a fifth varistor, a seventh resistor, an eighth resistor, and a voltage comparator. The fifth varistor is connected to the conduction control module. The first end of the seventh resistor is connected to the fifth varistor. The second end of the seventh resistor and the first end of the eighth resistor are connected together and connected to the non-inverting input of the voltage comparator. The inverting input of the voltage comparator is connected to the second power supply. The output of the voltage comparator is connected to the measurement and calculation module.

2. The self-testing device for the input impedance of an instrument according to claim 1, characterized in that, When the measuring instrument is in the safe input detection state, the first control switch, the third control switch, the fourth control switch and the fifth control switch are all placed at the first contact terminal, and the second control switch is placed at the third contact terminal.

3. The self-testing device for the input impedance of an instrument according to claim 1, characterized in that, When the measuring instrument is in the non-impedance branch self-test state, the first control switch, the second control switch, and the third control switch are all placed at the third contact terminal, and the fourth control switch is placed at the first contact terminal.

4. The self-testing device for the input impedance of an instrument according to claim 1, characterized in that, When the measuring instrument is in the input impedance self-test state, the second, third, fourth and fifth control switches are all placed at the third contact terminal, and the first control switch is placed at the first contact terminal.

5. The self-testing device for the input impedance of an instrument according to claim 1, characterized in that, The measurement calculation module includes an ADC and an MCU. The ADC is used to receive the signal to be measured sent by the measurement network selection module and send it to the MCU for calculation.

6. The self-testing device for the input impedance of an instrument according to claim 1, characterized in that, The measurement network selection module includes a data selector, the first and second ends of which are connected to the conduction control module, and the third end of which is connected to the measurement calculation module.

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