CN211235987U - Digital multi-purpose meter - Google Patents
Digital multi-purpose meter Download PDFInfo
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- CN211235987U CN211235987U CN201921888614.2U CN201921888614U CN211235987U CN 211235987 U CN211235987 U CN 211235987U CN 201921888614 U CN201921888614 U CN 201921888614U CN 211235987 U CN211235987 U CN 211235987U
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Abstract
The utility model relates to the field of measuring instruments, a digital multimeter is disclosed, including impedance amplifier, the AD converter, the button input unit, LCD and microprocessor, the AD converter includes voltage comparison module and DA module, analog voltage is inserted to impedance amplifier's input, impedance amplifier's output and voltage comparison module's input are connected, voltage comparison module's output, button input unit's output and LCD's input all are connected with microprocessor, the input of DA module is connected with microprocessor, the output of DA module is connected with voltage comparison module's input; the voltage comparison module comprises an analog voltage input end, a voltage comparator, a first capacitor, a first resistor, a power supply, a second resistor and a first diode, and the DA module comprises a second capacitor, a third resistor and a fourth resistor. Implement the utility model discloses, following beneficial effect has: the safety and the reliability of the analog-digital conversion circuit part are high.
Description
Technical Field
The utility model relates to a measuring instrument field, in particular to digital multimeter.
Background
Digital multimeters are electronic instruments used in electrical measurements. It may have many special functions, but the main function is to measure voltage, resistance and current. The digital multimeter is also called a comprehensive watt-hour meter, has multiple functions, and can measure parameters of each phase voltage, each current, each active power, each reactive power, each frequency, each electric energy and the like of three phases at one time. Some analog-to-digital conversion circuits of the digital multimeters in the prior art are partially lack of corresponding circuit protection functions, such as: the lack of current-limiting protection results in lower safety and reliability of the analog-to-digital conversion circuit part.
SUMMERY OF THE UTILITY MODEL
The to-be-solved technical problem of the present invention is to provide a digital multimeter having high safety and reliability for the analog-to-digital conversion circuit part, in view of the above-mentioned drawbacks of the prior art.
The utility model provides a technical scheme that its technical problem adopted is: constructing a digital multimeter, which comprises an impedance amplifier, an A/D converter, a key input unit, a liquid crystal display and a microprocessor, wherein the A/D converter comprises a voltage comparison module and a DA module, the input end of the impedance amplifier is connected with an analog voltage, the output end of the impedance amplifier is connected with the input end of the voltage comparison module, the output end of the key input unit and the input end of the liquid crystal display are all connected with the microprocessor, the input end of the DA module is connected with the microprocessor, and the output end of the DA module is connected with the input end of the voltage comparison module;
the voltage comparison module comprises an analog voltage input end, a voltage comparator, a first capacitor, a first resistor, a power supply, a second resistor and a first diode, the DA module comprises a second capacitor, a third resistor and a fourth resistor, one end of the first resistor is connected with the analog voltage input end, the analog voltage input end is connected with the output end of the impedance amplifier, the other end of the first resistor is respectively connected with one end of the first capacitor and the non-inverting input end of the voltage comparator, the other end of the first capacitor is grounded, the power supply end of the voltage comparator is respectively connected with the power supply, one end of the second resistor and a second pin of the microprocessor, the output end of the voltage comparator is connected with the anode of the first diode, the cathode of the first diode is respectively connected with the other end of the second resistor and the third pin of the microprocessor, the voltage comparator is characterized in that the inverting input end of the voltage comparator is respectively connected with one end of the second capacitor, one end of the third resistor and one end of the fourth resistor, the other end of the second capacitor, the grounding end of the voltage comparator, the fourth pin of the microprocessor and the other end of the third resistor are all grounded, and the other end of the fourth resistor is connected with the fifth pin of the microprocessor.
In the digital multimeter of the present invention, the first diode has a model of S-352T.
In the digital multimeter of the present invention, the voltage comparison module further comprises a fifth resistor, one end of the fifth resistor is connected to the power supply, and the other end of the fifth resistor is connected to the power supply end of the voltage comparator.
In the digital multimeter of the present invention, the resistance of the fifth resistor is 36k Ω.
In the digital multimeter of the present invention, the voltage supplied by the power supply is 3.3V.
In the digital multimeter of the present invention, the key input unit is connected to the eighth pin of the microprocessor.
In the digital multimeter of the present invention, the liquid crystal display is connected to the sixth pin of the microprocessor.
Implement the utility model discloses a digital multimeter has following beneficial effect: the device is provided with an impedance amplifier, an A/D converter, a key input unit, a liquid crystal display and a microprocessor, wherein the A/D converter comprises a voltage comparison module and a DA module; the voltage comparison module comprises an analog voltage input end, a voltage comparator, a first capacitor, a first resistor, a power supply source, a second resistor and a first diode, the DA module comprises a second capacitor, a third resistor and a fourth resistor, and the first diode is used for current limiting protection, so that the safety and the reliability of the analog-to-digital conversion circuit part are high.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic structural diagram of an embodiment of the digital multimeter of the present invention;
fig. 2 is a schematic circuit diagram of the a/D converter in the embodiment.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.
In the embodiment of the digital multimeter of the present invention, the schematic structural diagram of the digital multimeter is shown in fig. 1. In fig. 1, the digital multimeter includes an impedance amplifier 1, an a/D converter 2, a key input unit 3, a liquid crystal display 4, and a microprocessor U1, wherein the a/D converter 2 includes a voltage comparison module 21 and a DA module 22, an analog voltage is connected to an input terminal of the impedance amplifier 1, an output terminal of the impedance amplifier 1 is connected to an input terminal of the voltage comparison module 21, an output terminal of the key input unit 3, and an input terminal of the liquid crystal display 4 are all connected to a microprocessor U1, an input terminal of the DA module 22 is connected to a microprocessor U1, and an output terminal of the DA module 22 is connected to an input terminal of the voltage comparison module 21.
Parameters can be input through the key input unit 3, voltage is input into the impedance amplifier 1 at first when input, input impedance is improved, the impedance amplifier is convenient to be used by matching with high-voltage measuring devices such as a high-voltage divider and the like, the impedance amplifier 1 can be externally connected with other high-precision digital multimeters, and measuring precision is improved. The signals passing through the impedance amplifier 1 are subjected to analog-to-digital conversion through the A/D converter 2 to obtain digital signals, the digital signals are input to the microprocessor U1 for processing, the microprocessor U1 can perform real-time linear adjustment through linear correction coefficients input by the key input unit 3, the liquid crystal display 4 is used for displaying various data, the key input unit 3 can realize human-computer interaction, and the microprocessor U1 is controlled to work.
The analog voltage is transmitted to the voltage comparison module 21 and the voltage comparison module 21 can transmit a level signal to the microprocessor U1. DA module 22 can feed back the signal output by microprocessor U1 to voltage comparison module 21.
In this embodiment, the impedance amplifier 1, the key input unit 3, the liquid crystal display 4, and the microprocessor U1 are all implemented by using the structure in the prior art, and the working principle thereof is also the working principle in the prior art, which is not described in detail herein.
Fig. 2 is a schematic circuit diagram of an a/D converter in this embodiment, in fig. 2, the voltage comparison module 21 includes an analog voltage input terminal Vin, a voltage comparator a1, a first capacitor C1, a first resistor R1, a power supply VCC, a second resistor R2, and a first diode D1, the DA module 22 includes a second capacitor C2, a third resistor R3, and a fourth resistor R4, wherein one end of the first resistor R1 is connected to the analog voltage input terminal Vin, the analog voltage input terminal Vin is connected to an output terminal of the impedance amplifier 1, the other end of the first resistor R1 is connected to one end of the first capacitor C1 and a non-inverting input terminal of the voltage comparator a1, the other end of the first capacitor C1 is grounded, power supply terminals of the voltage comparator a1 are connected to the power supply VCC, one end of the second resistor R2 and a second pin of the microprocessor U1, an output terminal of the voltage comparator a1 is connected to an anode of the first diode D1, the cathode of the first diode D1 is connected to the other end of the second resistor R2 and the third pin of the microprocessor U1, the inverting input terminal of the voltage comparator a1 is connected to one end of the second capacitor C2, one end of the third resistor R3 and one end of the fourth resistor R4, the other end of the second capacitor C2, the ground terminal of the voltage comparator a1, the fourth pin of the microprocessor U1 and the other end of the third resistor R3 are all grounded, and the other end of the fourth resistor R4 is connected to the fifth pin of the microprocessor U1.
In this embodiment, the first diode D1 is a current limiting diode for current limiting protection. The current limiting protection principle is as follows: when the current of the branch in which the first diode D1 is located is large, the current of the branch in which the first diode D1 is located can be reduced by the first diode D1, so that the branch can be kept in a normal operating state, and the components in the circuit cannot be burnt out due to the large current, so that the safety and reliability of the circuit are high. It should be noted that in the present embodiment, the first diode D1 has a model number S-352T. Of course, in practical applications, the first diode D1 may also be another type of diode with similar functions.
The analog voltage is filtered by a first capacitor C1 and a first resistor R1 and then reaches the non-inverting input terminal of the voltage comparator a 1. Using the third pin of the microprocessor U1 as an input and the fifth pin as an output, the voltage comparator A1 could send a level signal to the microprocessor U1. The third pin of the microprocessor U1 is connected to the power supply VCC after being connected in series with the second resistor R2, and the second resistor R2 plays a role of pulling up. A level signal sent from the fifth pin of the microprocessor U1 is divided by the third resistor R3 and the fourth resistor R4, filtered by the second capacitor C2, and then reaches the inverting input terminal of the voltage comparator a1, thereby completing a DA conversion.
The microprocessor U1 detects the level of the third pin at regular intervals, controls the fifth pin to output a high level signal when the third pin is at a high level, and otherwise outputs a low level signal. The microprocessor U1 clears the AD conversion value each time AD conversion is started, adds 1 to the AD conversion value each time a level signal of the third pin is detected to be high, and completes one time of AD conversion with a resolution of N bits when the number of consecutive detections reaches N times of 2. When N is 16, the conversion is 16-bit AD conversion, the conversion speed is not fast, but the resolution is high, the application requirement of temperature acquisition is met, and the microprocessor U1 can use a single chip microcomputer of an original system of the instrument and only needs 2 IO ports. The utility model discloses convert analog signal to digital signal, can reach 16 AD conversions, the not fast but resolution ratio of conversion rate is very high, only needs single power supply, and it is simple to have a circuit, low cost's advantage.
In this embodiment, the voltage provided by the power supply VCC is 3.3V. The key input unit 3 is connected to the eighth pin of the microprocessor U1. The liquid crystal display 4 is connected to the sixth pin of the microprocessor U1.
In this embodiment, the voltage comparing module 21 further includes a fifth resistor R5, one end of the fifth resistor R5 is connected to the power supply VCC, and the other end of the fifth resistor R5 is connected to the power supply terminal of the voltage comparator a 1. The fifth resistor R5 is a current limiting resistor for current limiting protection. The current limiting protection principle is as follows: when the current of the branch where the fifth resistor R5 is located is large, the current of the branch where the fifth resistor R5 is located can be reduced by the fifth resistor R5, so that the branch can be kept in a normal operating state, and the components in the circuit cannot be burned out due to the large current, so that the safety and reliability of the circuit are further enhanced. It should be noted that, in the present embodiment, the resistance of the fifth resistor R5 is 36k Ω. Of course, in practical applications, the resistance of the fifth resistor R5 may be adjusted according to specific situations, that is, the resistance of the fifth resistor R5 may be increased or decreased according to specific situations.
In short, in this embodiment, since the voltage comparison module 21 is provided with the current-limiting diode, the safety and reliability of the analog-to-digital conversion circuit portion are high.
The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A digital multimeter is characterized by comprising an impedance amplifier, an A/D converter, a key input unit, a liquid crystal display and a microprocessor, wherein the A/D converter comprises a voltage comparison module and a DA module, the input end of the impedance amplifier is connected with an analog voltage, the output end of the impedance amplifier is connected with the input end of the voltage comparison module, the output end of the key input unit and the input end of the liquid crystal display are all connected with the microprocessor, the input end of the DA module is connected with the microprocessor, and the output end of the DA module is connected with the input end of the voltage comparison module;
the voltage comparison module comprises an analog voltage input end, a voltage comparator, a first capacitor, a first resistor, a power supply, a second resistor and a first diode, the DA module comprises a second capacitor, a third resistor and a fourth resistor, one end of the first resistor is connected with the analog voltage input end, the analog voltage input end is connected with the output end of the impedance amplifier, the other end of the first resistor is respectively connected with one end of the first capacitor and the non-inverting input end of the voltage comparator, the other end of the first capacitor is grounded, the power supply end of the voltage comparator is respectively connected with the power supply, one end of the second resistor and a second pin of the microprocessor, the output end of the voltage comparator is connected with the anode of the first diode, the cathode of the first diode is respectively connected with the other end of the second resistor and the third pin of the microprocessor, the voltage comparator is characterized in that the inverting input end of the voltage comparator is respectively connected with one end of the second capacitor, one end of the third resistor and one end of the fourth resistor, the other end of the second capacitor, the grounding end of the voltage comparator, the fourth pin of the microprocessor and the other end of the third resistor are all grounded, and the other end of the fourth resistor is connected with the fifth pin of the microprocessor.
2. The digital multimeter of claim 1, wherein the first diode is model number S-352T.
3. The digital multimeter of claim 2, wherein the voltage comparison module further comprises a fifth resistor, one end of the fifth resistor being connected to the power supply, the other end of the fifth resistor being connected to a power supply terminal of the voltage comparator.
4. The digital multimeter of claim 3, wherein the fifth resistor has a resistance of 36 kq.
5. The digital multimeter of any of claims 1-4, wherein the power supply provides a voltage of 3.3V.
6. The digital multimeter of any one of claims 1 to 4, wherein the key input unit is connected to an eighth pin of the microprocessor.
7. The digital multimeter of any of claims 1-4, wherein the liquid crystal display is connected to a sixth pin of the microprocessor.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201921888614.2U CN211235987U (en) | 2019-11-04 | 2019-11-04 | Digital multi-purpose meter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201921888614.2U CN211235987U (en) | 2019-11-04 | 2019-11-04 | Digital multi-purpose meter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN211235987U true CN211235987U (en) | 2020-08-11 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201921888614.2U Active CN211235987U (en) | 2019-11-04 | 2019-11-04 | Digital multi-purpose meter |
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| Country | Link |
|---|---|
| CN (1) | CN211235987U (en) |
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2019
- 2019-11-04 CN CN201921888614.2U patent/CN211235987U/en active Active
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