CN116263466A - Direct current constant current type ADC front-end circuit for detecting resistance value - Google Patents

Direct current constant current type ADC front-end circuit for detecting resistance value Download PDF

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Publication number
CN116263466A
CN116263466A CN202111527940.2A CN202111527940A CN116263466A CN 116263466 A CN116263466 A CN 116263466A CN 202111527940 A CN202111527940 A CN 202111527940A CN 116263466 A CN116263466 A CN 116263466A
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resistor
operational amplifier
constant current
circuit
buffer
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Chinese (zh)
Inventor
廖无限
李哲
彭思程
谌安平
张超
熊梓辰
张炎钦
黄勃
谭学武
唐忠健
谢豪
张旭
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Hunan University of Technology
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Hunan University of Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
    • G01R1/28—Provision in measuring instruments for reference values, e.g. standard voltage, standard waveform
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
    • G01R1/36—Overload-protection arrangements or circuits for electric measuring instruments
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/08—Measuring resistance by measuring both voltage and current
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/14—Measuring resistance by measuring current or voltage obtained from a reference source
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Resistance Or Impedance (AREA)

Abstract

The invention discloses an ADC (analog-to-digital converter) front-end circuit for detecting resistance of a direct-current constant-current type, which comprises a buffer 1, a buffer 2, a constant-current generator, a resistor Rx to be detected and a signal end V_ADC; the buffer 1 and the buffer 2 are used for resistance value conversion, and the constant current generator is used for generating a corresponding direct current constant current source. The direct current constant current type ADC pre-circuit for detecting the resistance value provided by the invention can replace a traditional four-wire method circuit on the premise of ensuring the precision and the efficiency, combines a current measuring circuit and a voltage measuring circuit into one, has an open circuit protection function, can detect the direct current resistance, and has the outstanding advantages of simpler circuit structure and lower hardware cost.

Description

Direct current constant current type ADC front-end circuit for detecting resistance value
Technical Field
The invention relates to the field of electric detection, in particular to a direct current constant current type ADC (analog to digital converter) front-end circuit for detecting resistance values of resistors.
Background
In the electrical detection field, the resistance value of a resistor is detected by using a common voltammetry, with the development of a digital circuit, the resistance value of the resistor is increasingly and universally measured digitally by using an Analog-to-digital converter (Analog-to-digital) technology in the electrical detection field, and compared with the traditional pointer voltammetry, the precision and the efficiency of digital measurement are greatly improved; currently, in digital measurement, one of the keys to improve measurement accuracy and efficiency is to improve ADC front-end circuitry; in addition, the four-wire method circuit is also one of the ADC front-end circuits that are more commonly used in the detection of resistance values.
The inventor finds in the process of realizing the embodiment of the invention:
(1) In the traditional four-wire method circuit, a current measuring loop and a voltage measuring loop are mutually independent, the circuit structure is relatively complex, and the cost is relatively high;
(2) In a conventional four-wire circuit, because a constant current source is adopted in a current measurement loop, a measured resistor must be considered to be incapable of being opened, otherwise, the safety of a signal conditioning circuit or a processor connected at the rear end of the resistor is endangered, and irreversible damage is caused.
In a word, in the current electrical detection field, an ADC pre-circuit used for replacing the traditional four-wire method is lacking, and on the premise of ensuring accuracy and efficiency, a current measurement loop and a voltage measurement loop are combined into one, so that the direct-current resistor can be detected, an open-circuit protection circuit is arranged, and the circuit has the outstanding advantages of simpler circuit structure and lower hardware cost.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a direct current constant current type ADC (analog to digital converter) front-end circuit for detecting resistance values, which comprises the following specific technical scheme:
an ADC front-end circuit for detecting resistance of a resistor comprises a buffer 1, a buffer 2, a constant current generator, a resistor Rx to be detected and a signal end V_ADC;
the circuit structures of the buffer 1 and the buffer 2 are the same, and the voltage followers formed by operational amplifiers are all used for resistance conversion, namely, measurement errors are reduced in a mode of increasing input resistance and reducing output resistance, the buffer 1 comprises an operational amplifier U1, and the buffer 2 comprises an operational amplifier U3;
the constant current generator is used for generating a corresponding direct current constant current source after circuit conversion, and comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, an operational amplifier U2 and a constant current preset resistor Rs;
one end of the resistor Rx to be tested is connected with the power ground, the other end of the resistor Rx to be tested is connected with the non-inverting input end of the operational amplifier U1, one end of the constant current preset resistor Rs and the non-inverting input end of the operational amplifier U3, and the connected contact point is set as a port Ux; the output end of the operational amplifier U1 is connected with the inverting input end of the operational amplifier U, and is also connected with one end of a resistor R1, the other end of the resistor R1 is connected with one end of a resistor R2 and the non-inverting input end of the operational amplifier U2, the other end of the resistor R2 is connected with a power supply Vcc, the inverting input end of the operational amplifier U2 is connected with one end of a resistor R3 and one end of a resistor R4, the other end of the resistor R3 is connected with the power supply ground, and the other end of the resistor R4 is connected with the output end of the operational amplifier U2 and the other end of a constant current preset resistor Rs; the output end of the operational amplifier U3 is connected with the inverting input end of the operational amplifier U and is also connected with the signal end V_ADC.
Further, a resistor R5 and a zener diode VD are newly added between the output end of the operational amplifier U3 and the signal end v_adc, for overvoltage protection when the resistor Rx to be tested is open; the output end of the operational amplifier U3 is connected with one end of a resistor R5, the other end of the resistor R5 is connected with the cathode of the voltage stabilizing diode VD and the signal end V_ADC, and the anode of the voltage stabilizing diode VD is connected with the power ground.
The invention has the beneficial effects that the direct current constant current type ADC pre-circuit for detecting the resistance value can replace the traditional four-wire method circuit on the premise of ensuring the precision and the efficiency, combines a current measuring circuit and a voltage measuring circuit into one, has an open circuit protection function, can detect the direct current resistance, and has the outstanding advantages of simpler circuit structure and lower hardware cost.
Drawings
FIG. 1 is a simplified equivalent schematic diagram of a conventional four-wire method for measuring resistance.
Fig. 2 is a schematic diagram of an ADC front-end circuit for detecting resistance of a resistor according to the present invention.
Fig. 3 is a schematic diagram of an ADC front-end circuit for detecting resistance of a resistor according to another exemplary embodiment of the present invention.
Detailed Description
The following detailed description of the present invention will provide further details in order to make the above-mentioned objects, features and advantages of the present invention more comprehensible. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit or scope of the invention, which is therefore not limited to the specific embodiments disclosed below.
Fig. 1 is a simplified equivalent schematic diagram of a traditional four-wire method for measuring resistance, wherein a resistor Rx is a resistor to be measured, a resistor R1 and a resistor R4 are equivalent resistors of a detection line of a current detection loop, and a resistor R2 and a resistor R3 are equivalent resistors of a detection line of a voltage detection loop; the measured resistor Rx, the resistor R1, the resistor R4 and the equivalent current measuring device A form a current detection loop, and the measured resistor Rx, the resistor R2, the resistor R3 and the equivalent voltage detecting device V form a voltage detection loop; it can be seen that the simplified traditional four-wire method circuit principle is simpler, but the current measuring loop and the voltage measuring loop are mutually independent, the circuit structure is relatively complex, and the cost is relatively high; in addition, the equivalent current measuring device a is mostly composed of a constant current source, and the problem that the resistor Rx to be measured cannot be opened in practical application must be solved, so there is room for improvement in the conventional four-wire method circuit.
Fig. 2 is a schematic diagram of a dc constant-current ADC front-end circuit for detecting resistance of a resistor, which includes a buffer 1, a buffer 2, a constant-current generator, a resistor to be detected Rx and a signal terminal v_adc;
the circuit structures of the buffer 1 and the buffer 2 are the same, and the voltage followers formed by operational amplifiers are all used for resistance conversion, namely, measurement errors are reduced in a mode of increasing input resistance and reducing output resistance, the buffer 1 comprises an operational amplifier U1, and the buffer 2 comprises an operational amplifier U3;
the constant current generator is used for generating a corresponding direct current constant current source after circuit conversion, and comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, an operational amplifier U2 and a constant current preset resistor Rs;
one end of the resistor Rx to be tested is connected with the power ground, the other end of the resistor Rx to be tested is connected with the non-inverting input end of the operational amplifier U1, one end of the constant current preset resistor Rs and the non-inverting input end of the operational amplifier U3, and the connected contact point is set as a port Ux; the output end of the operational amplifier U1 is connected with the inverting input end of the operational amplifier U, and is also connected with one end of a resistor R1, the other end of the resistor R1 is connected with one end of a resistor R2 and the non-inverting input end of the operational amplifier U2, the other end of the resistor R2 is connected with a power supply Vcc, the inverting input end of the operational amplifier U2 is connected with one end of a resistor R3 and one end of a resistor R4, the other end of the resistor R3 is connected with the power supply ground, and the other end of the resistor R4 is connected with the output end of the operational amplifier U2 and the other end of a constant current preset resistor Rs; the output end of the operational amplifier U3 is connected with the inverting input end of the operational amplifier U and is also connected with the signal end V_ADC.
Setting the output end of the operational amplifier U1 as UB, setting the non-inverting input end of the operational amplifier U2 as UC+, setting the inverting input end of the operational amplifier U2 as UC-, setting the output end of the operational amplifier U2 as UD, and setting the current flowing through the constant current preset resistor Rs as Is; the operational amplifier U1 and the operational amplifier U3 are voltage follower circuits, the input resistance of the voltage follower circuits approaches infinity, and the current Is flowing through the constant current preset resistor Rs can be considered to completely pass through the resistor Rx to be detected and then flow into the power supply ground;
namely, when the resistor Rx to be measured Is connected, the relation between the output current Is in the constant current generator and the voltage value of the power supply Vcc Is deduced as follows:
setting resistor
Figure 221050DEST_PATH_IMAGE001
(1)
According to the superposition principle, then
Figure 92186DEST_PATH_IMAGE002
(2)
Figure 544027DEST_PATH_IMAGE003
(3)
According to the principle of deficiency and shortness, there are
Figure 657345DEST_PATH_IMAGE004
(4)
I.e.
Figure 206138DEST_PATH_IMAGE005
(5)
Since the operational amplifier U1 is a voltage follower connection, there is
Figure 497442DEST_PATH_IMAGE006
(6)
I.e.
Figure 184382DEST_PATH_IMAGE007
(7)
Namely, the voltage at two ends of the resistor Rx to be measured Is the voltage value of the power supply Vcc, and the output current Is in the constant current generator Is
Figure 852124DEST_PATH_IMAGE008
(8)
So the current of the resistor Rx to be measured Is also constant Is, namely the resistance of the resistor Rx to be measured can be calculated by measuring the voltages at the two ends of the resistor Rx to be measured
Figure 521002DEST_PATH_IMAGE009
(9)
The voltage value of the power supply Vcc Is known, the output current Is of the direct current constant current source can be determined by presetting the resistance value of the constant current preset resistor Rs, the direct current constant current source Is processed by the signal conditioning circuit at the rear end and then Is sent to the processor on the premise of being connected to the resistor Rx to be detected, or the direct current Is directly sent to the processor, and the resistance value of the resistor Rx to be detected can be obtained after the operation according to Rx=Ux/Is in the processor as long as the value of Ux Is measured.
Fig. 3 is a schematic diagram of another typical dc-dc type ADC pre-circuit for detecting resistance of a resistor, in which a resistor R5 and a zener diode VD are newly added between the output end of the operational amplifier U3 and the signal end v_adc for overvoltage protection when the resistor Rx to be tested is open; the output end of the operational amplifier U3 is connected with one end of a resistor R5, the other end of the resistor R5 is connected with the cathode of the voltage stabilizing diode VD and the signal end V_ADC, and the anode of the voltage stabilizing diode VD is connected with the power ground.
Because the resistor R5 and the zener diode VD form an overvoltage limiting protection circuit, the signal terminal V_ADC is limited within the stable voltage Uz of the zener diode VD; in contrast, when the resistor Rx to be tested is not connected, and the resistor R5 and the zener diode VD are not connected, the resistance corresponding to the resistor Rx to be tested is infinity, the voltage on the port Ux increases to approach the power voltage value of the operational amplifier U2, and the voltage may endanger the safety of the signal conditioning circuit or the processor connected to the rear end of the output terminal v_adc, i.e. once the voltage value is greater than the limit voltage values of the two input terminals, irreversible damage is caused, so that the overvoltage limiting protection circuit formed by the resistor R5 and the zener diode VD is increased, and the phenomenon can be reliably avoided.

Claims (2)

1. The direct current constant current type ADC pre-circuit for detecting the resistance value of the resistor is characterized by comprising a buffer 1, a buffer 2, a constant current generator, a resistor Rx to be detected and a signal end V_ADC;
the circuit structures of the buffer 1 and the buffer 2 are the same, and the voltage followers formed by operational amplifiers are all used for resistance conversion, namely, measurement errors are reduced in a mode of increasing input resistance and reducing output resistance, the buffer 1 comprises an operational amplifier U1, and the buffer 2 comprises an operational amplifier U3;
the constant current generator is used for generating a corresponding direct current constant current source after circuit conversion, and comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, an operational amplifier U2 and a constant current preset resistor Rs;
one end of the resistor Rx to be tested is connected with the power ground, the other end of the resistor Rx to be tested is connected with the non-inverting input end of the operational amplifier U1, one end of the constant current preset resistor Rs and the non-inverting input end of the operational amplifier U3, and the connected contact point is set as a port Ux; the output end of the operational amplifier U1 is connected with the inverting input end of the operational amplifier U, and is also connected with one end of a resistor R1, the other end of the resistor R1 is connected with one end of a resistor R2 and the non-inverting input end of the operational amplifier U2, the other end of the resistor R2 is connected with a power supply Vcc, the inverting input end of the operational amplifier U2 is connected with one end of a resistor R3 and one end of a resistor R4, the other end of the resistor R3 is connected with the power supply ground, and the other end of the resistor R4 is connected with the output end of the operational amplifier U2 and the other end of a constant current preset resistor Rs; the output end of the operational amplifier U3 is connected with the inverting input end of the operational amplifier U and is also connected with the signal end V_ADC.
2. The ADC pre-circuit for detecting resistance value of a resistor according to claim 1, wherein a resistor R5 and a zener diode VD are newly added between the output terminal of the operational amplifier U3 and the signal terminal v_adc for overvoltage protection when the resistor Rx to be detected is open; the output end of the operational amplifier U3 is connected with one end of a resistor R5, the other end of the resistor R5 is connected with the cathode of the voltage stabilizing diode VD and the signal end V_ADC, and the anode of the voltage stabilizing diode VD is connected with the power ground.
CN202111527940.2A 2021-12-15 2021-12-15 Direct current constant current type ADC front-end circuit for detecting resistance value Pending CN116263466A (en)

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Application Number Priority Date Filing Date Title
CN202111527940.2A CN116263466A (en) 2021-12-15 2021-12-15 Direct current constant current type ADC front-end circuit for detecting resistance value

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CN116263466A true CN116263466A (en) 2023-06-16

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