CN113030585B - Capacitance measuring device and method - Google Patents
Capacitance measuring device and method Download PDFInfo
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- CN113030585B CN113030585B CN202110292365.6A CN202110292365A CN113030585B CN 113030585 B CN113030585 B CN 113030585B CN 202110292365 A CN202110292365 A CN 202110292365A CN 113030585 B CN113030585 B CN 113030585B
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- 238000000034 method Methods 0.000 title claims abstract description 23
- 239000003990 capacitor Substances 0.000 claims abstract description 144
- 238000012360 testing method Methods 0.000 claims abstract description 110
- 238000005259 measurement Methods 0.000 claims abstract description 81
- 238000002955 isolation Methods 0.000 claims description 26
- 238000007599 discharging Methods 0.000 claims description 14
- 238000000691 measurement method Methods 0.000 claims description 10
- 238000006243 chemical reaction Methods 0.000 description 5
- 230000008054 signal transmission Effects 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000008707 rearrangement Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
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- 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
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2605—Measuring capacitance
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/26—Testing of individual semiconductor devices
- G01R31/2601—Apparatus or methods therefor
Abstract
The invention discloses a capacitance measuring device and a capacitance measuring method. The capacitance measuring device includes: test bench, selection module, control module and power module. The test bench comprises a start button and a voltage measurement unit; the start button is used for outputting a start measurement signal; the voltage measuring unit is used for measuring the voltages at two ends of the measured capacitor; the selection module comprises a selection circuit and a resistor, and the resistor is respectively connected with the selection circuit and the test bench; the selection module is used for selecting the sizes of the test voltage and the output current according to the rated parameters of the tested capacitor; the control module is respectively connected with the start button, the voltage measurement unit and the selection circuit, and is used for starting measurement according to a start measurement signal, timing the charging time of the measured capacitor and calculating the capacitance value of the measured capacitor according to the voltage at two ends of the measured capacitor, the charging time and the resistance value of the resistor; the power module is used for supplying power to the control module and the selection module. The invention can provide test environments of various capacitors and improve the universality of the capacitance measuring device.
Description
Technical Field
The embodiment of the invention relates to the technical field of measurement, in particular to a capacitance measurement device and a capacitance measurement method.
Background
The capacitor belongs to a common electronic component. In the use process, the capacitance value of the capacitor has the characteristic of changing along with the change of the use environment and the application voltage; moreover, since capacitor shipment adopts a sampling inspection mode and the like, even if capacitors are shipped in the same batch, the problem of yield rate may exist, and the capacitance value of the capacitor may deviate. Therefore, when the capacitor has higher precision requirement in use, the capacitor is required to be checked, so that the stability and precision of the circuit are ensured. In general, when the test environment meets the rated parameters of the capacitor, the obtained capacitance value is more accurate. However, the capacitance measuring device in the prior art can only measure one or a class of capacitance, and has the problem of poor universality.
Disclosure of Invention
The embodiment of the invention provides a capacitance measuring device and a capacitance measuring method, which are used for providing test environments of various capacitances and improving the universality of the capacitance measuring device.
In a first aspect, an embodiment of the present invention provides a capacitance measurement device, including:
a test stand including a start button and a voltage measurement unit; the start button is used for outputting a start measurement signal; the voltage measuring unit is used for measuring the voltages at two ends of the measured capacitor;
the selection module comprises a selection circuit and a resistor, and the resistor is respectively connected with the selection circuit and the test bench; the selection module is used for selecting the sizes of the test voltage and the output current according to the rated parameters of the tested capacitor and transmitting the output current to the tested capacitor through the resistor;
the control module is respectively connected with the start button, the voltage measurement unit and the selection circuit; the control module is used for starting measurement according to the starting measurement signal, timing the charging time of the measured capacitor, and calculating the capacitance value of the measured capacitor according to the voltage at two ends of the measured capacitor, the charging time and the resistance value of the resistor;
the power module is respectively connected with the control module and the selection module and is used for supplying power to the control module and the selection module.
Optionally, the capacitance measurement device further includes: and the display module is connected with the control module and used for displaying the capacitance value of the tested capacitor.
Optionally, the test bench further comprises: a discharge switch and a discharge circuit; the discharging switch is connected between the tested capacitor and the discharging circuit, and the discharging circuit is used for discharging the tested capacitor.
Optionally, the selection circuit includes: the test voltage selection unit comprises a power supply end, a voltage state signal end and at least two output ends; the power end of the test voltage selection unit is connected with the power module, and the voltage state signal end of the test voltage selection unit is connected with the control module; the test voltage selecting unit is used for selecting a test voltage according to the rated voltage of the tested capacitor and outputting the test voltage from a corresponding output end;
the measuring range selecting and outputting unit comprises a starting signal end, a measuring range state signal end, an output end and at least two input ends; at least two input ends of the range selection and output unit are connected with at least two output ends of the test voltage selection unit in a one-to-one correspondence manner, a starting signal end and a range state signal end of the range selection and output unit are both connected with the control module, and an output end of the range selection and output unit is connected with the resistor; and the measuring range selecting and outputting unit is used for selecting a testing measuring range according to the rated capacitance of the tested capacitor and performing constant current output according to the testing range and a starting measuring signal output by the control module.
Optionally, the test voltage selecting unit further includes: a first selection switch and a voltage selection circuit; the first selection switch is connected with the voltage selection circuit, and the voltage selection circuit is used for selecting the output test voltage;
the range selection and output unit further includes: a second selection switch and a range selection circuit; the second selection switch is connected with the range selection circuit, and the range selection circuit is used for selecting the test range.
Optionally, the power module includes: the low dropout linear voltage regulator comprises an input end and an output end, wherein the input end of the low dropout linear voltage regulator is connected with direct current supply voltage, the output end of the low dropout linear voltage regulator is connected with the control module, and the low dropout linear voltage regulator is used for carrying out step-down processing on the direct current supply voltage and supplying power to the control module.
Optionally, the control module includes:
a control unit including a first end and a second end;
the first isolation unit comprises a first end and a second end, the first end of the first isolation unit is connected with the first end of the control unit, and the second end of the first isolation unit is connected with the selection module;
the second isolation unit comprises a first end and a second end, the first end of the second isolation unit is connected with the second end of the control unit, and the second end of the second isolation unit is connected with the start button and the voltage measurement unit.
In a second aspect, an embodiment of the present invention further provides a capacitance measurement method, where the capacitance measurement device provided in any embodiment of the present invention is used, and the capacitance measurement method includes:
the selection module selects the sizes of the test voltage and the output current according to the rated parameters of the tested capacitor;
the control module outputs a start measurement signal according to the received start measurement signal output by the start button;
a selection circuit in the selection module receives the starting measurement signal, and constant current output is carried out through a resistor to charge the tested capacitor; simultaneously, a voltage measuring unit in the test bench measures the voltages at two ends of the tested capacitor;
the control module counts the charging time of the tested capacitor; and calculating the capacitance value of the tested capacitor according to the voltage at the two ends of the tested capacitor, the charging time and the resistance value of the resistor.
Optionally, the control module counts the charging time of the measured capacitor, and calculates the capacitance value of the measured capacitor according to the voltage at two ends of the measured capacitor, the charging time and the resistance value of the resistor, including:
the control module starts timing when outputting the starting measurement signal;
the control module stops timing when the voltage at two ends of the tested capacitor reaches a preset threshold value;
and the control module calculates the capacitance value of the tested capacitor according to the charging time and the resistance value of the resistor.
Optionally, the preset threshold is 0.63 times of the full-power voltage value of the measured capacitor;
the calculating the capacitance value of the measured capacitor according to the charging time and the resistance value of the resistor comprises the following steps:
dividing the charging time by the resistance value of the resistor to obtain the capacitance value of the tested capacitor.
The capacitance measuring device provided by the embodiment of the invention is provided with a test board, a control module and a selection module, wherein the control module controls the selection module to start measurement after receiving a start measuring signal output by a start button on the test board; when there is no measurement demand, the control module may control the selection circuit not to output current, so as to reduce the power consumption of the measurement device. The selection module can select the sizes of the test voltage and the output current according to the rated parameters of the tested capacitor, so that the test environment is as close as possible to the optimal use environment of the tested capacitor, the measurement of the capacitance value is more accurate, and the measurement device can be suitable for the tested capacitors with different rated voltages or measuring ranges. Therefore, compared with the prior art, the embodiment of the invention can provide test environments for various capacitances and improve the universality of the capacitance measuring device.
Drawings
Fig. 1 is a schematic structural diagram of a capacitance measurement device according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of another capacitance measuring device according to an embodiment of the present invention;
FIG. 3 is a schematic flow chart of a capacitance measurement method according to an embodiment of the present invention;
fig. 4 is a flow chart of another capacitance measurement method according to an embodiment of the invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.
The embodiment of the invention provides a capacitance measuring device. Fig. 1 is a schematic structural diagram of a capacitance measurement device according to an embodiment of the present invention. Referring to fig. 1, the capacitance measuring apparatus includes: test station 110, selection module 120, control module 130, and power module 140.
Wherein the test stand 110 includes a start button 111 and a voltage measurement unit 112; the capacitance C to be measured is fixed on the surface of the test bench 110. The start button 111 is used to output a start measurement signal; the voltage measurement unit 112 is used for measuring the voltage across the measured capacitor. The selection module 120 comprises a selection circuit 121 and a resistor R, and the resistor R is respectively connected with the selection circuit 121 and the test bench 110; the resistor R is electrically connected with the tested capacitor C through the test bench 110, so that the selection circuit 121 can charge the tested capacitor C through the resistor R; the selection module 120 is configured to select the magnitude of the test voltage and the output current according to the rated parameter of the tested capacitor C, and transmit the output current to the tested capacitor C through the resistor R. The control module 130 is connected to the start button 111, the voltage measurement unit 112, and the selection circuit 121, respectively; the control module 130 is configured to start measurement according to the start measurement signal, time the charging time of the measured capacitor C, and calculate the capacitance of the measured capacitor C according to the voltage at both ends of the measured capacitor C, the charging time, and the resistance of the resistor R. The power module 140 is connected to the control module 130 and the selection module 120, respectively, for supplying power to the control module 130 and the selection module 120.
Illustratively, the measurement process using the capacitance measuring device may include:
the capacitance C to be measured is fixed to the test stand 110. The selection module 120 selects a test environment according to rated parameters of the tested capacitor C; wherein the selection module 120 may be manually controlled by a worker; the selection module 120 may select a test voltage according to the rated voltage of the tested capacitor C, select a test range according to the rated capacitance of the tested capacitor C, and transmit relevant status information such as the test voltage and the test range to the control module 130; alternatively, the state selection of the selection module 120 may be directly controlled by the control module 130, so long as the control module 130 is guaranteed to calculate the capacitance value of the measured capacitor C according to the selection state of the selection module 120. The above process may be regarded as a preparation work in the measurement process, and after the above debugging is completed, the start button 111 on the test stand 110 is pressed, and the test stand 110 transmits a start measurement signal to the control module 130; after the control module 130 receives the start measurement signal, the start measurement signal is transmitted to the selection module 120, so that the selection module 130 performs constant current output to charge the measured capacitor C; the voltage measuring unit 112 always measures the voltage at two ends of the capacitor C to be measured in the test process, and transmits the voltage value to the control module 130; the control module 130 counts the charging time of the measured capacitor C in the process of charging the measured capacitor C; and the capacitance value of the measured capacitor C is calculated according to the voltage at the two ends of the measured capacitor C, the charging time and the resistance value of the resistor R.
Alternatively, the control module 130 may calculate the capacitance value of the measured capacitor C according to an RC constant calculation formula. The specific explanation is as follows: recording the full-charge voltage value of the measured capacitor C as Vu, the capacitance value of the measured capacitor C as C1, the resistance value of the resistor R as R1, the initial voltage value of the measured capacitor C as 0, and the voltage Vt at two ends of the measured capacitor C at any time t in the charging process can be expressed as: vt=vu (1-e -t/(R1*C1) ). The full voltage Vu of the capacitor C to be measured and the resistance R1 of the resistor R can be known, and the capacitance C1 of the capacitor C to be measured can be obtained by measuring the voltage Vt corresponding to the time t and the time t.
Optionally, the resistor R is a high-precision resistor, so that the accuracy of a measurement result is ensured; the selection of the resistor R may vary according to the nominal parameters of the capacitor C being measured. Alternatively, the start button 111 may be connected only to the control module 130 for generating a start measurement signal without affecting the charging circuit of the measured capacitor C; alternatively, the start button 111 may be connected between the resistor R and the capacitor C to be tested, which has the function of sending a signal to the control module 130, and also makes the charging circuit of the capacitor C to be tested conductive only when the start button 111 is closed, and the selection circuit 121 may charge the capacitor C to be tested through the resistor R, so as to improve the safety of the device, and simultaneously cut off the charging circuit of the capacitor C to be tested when the test is not needed, so as to reduce the power consumption. Alternatively, the voltage measuring unit 122 may be a measuring device having a voltage measuring function, such as a multimeter. Optionally, a voltage conversion device may be included in the selection module 120 to change the test voltage according to the rated voltage of the capacitor C under test. Alternatively, the control module 130 may be formed by a control chip (such as STM8S 003); the control module 130 may include a timer, such as a timer. Generally, the power supply voltage required by the control module 130 is low (such as DC 5V or DC 3.3V), and the power supply voltage of the selection module 120 may be high or low, so the power module 140 may also include a voltage conversion device to meet the power supply requirements of different modules.
In the capacitance measuring device provided by the embodiment of the invention, a test board 110, a control module 130 and a selection module 120 are provided, wherein the control module 130 controls the selection module 120 to start measurement after receiving a start measurement signal output by a start button 111 on the test board 110; when there is no measurement demand, the control module 130 may control the selection circuit 121 not to output current to reduce the power consumption of the measurement device. In addition, the selection module 120 can select the test voltage and the output current according to the rated parameters of the tested capacitor C, so that the test environment is as close as possible to the optimal use environment of the tested capacitor C, the measurement of the capacitance value is more accurate, and the measurement device can be suitable for the tested capacitors C with different rated voltages or ranges. Therefore, the embodiment of the invention can provide test environments for various capacitances and improve the universality of the capacitance measuring device.
Alternatively, to simplify the calculation process of the control module 130, the following settings may be made based on the above embodiments:
in general, the measured capacitor C is considered to be full after a charging process of 3-5 RC time constants. Taking RC time constant (in this embodiment, R1×c1) as a time unit, when charging to a time unit, t1=r1×c1; the voltage of the capacitor C to be measured, vt1=vu (1-e -t/(R1*C1) )＝Vu*(1-e -1 ) At this time, vt is about 0.63 times the full voltage Vu of the capacitor C to be measured (which may be expressed as vt1=0.63 Vu). Similarly, according to the charging formula of the measured capacitor C, it can be obtained that when t2=2r1×c1, vt2=0.86 Vu; when t3=3×r1×c1, vt3=0.95 Vu, and the likePushing. Therefore, the control module 130 can calculate the capacitance value of the measured capacitor C according to the corresponding relationship between the real-time voltage value Vt of the measured capacitor C and the time unit. For example, the control module 130 starts timing when sending out the start measurement signal, and stops timing when the voltage value (i.e. Vt) fed back by the voltage measurement unit 112 reaches 0.63Vu, and then the charging time recorded at this time is a time unit corresponding to the resistance value R1 and the capacitance value C1; since the resistance R1 of the resistor R is known, the control module 130 only needs to divide the charging time by the resistance R1 to obtain the capacitance C1. Similarly, if the control module 130 stops timing when the voltage value (i.e. Vt) fed back by the voltage measurement unit 112 reaches 0.86Vu, the capacitance C1 is obtained by dividing the charging time by the resistance R1 of two times, and so on. That is, in the embodiment of the invention, the voltage values at two ends of the measured capacitor C are used as the condition for stopping timing, and the capacitance value of the measured capacitor C can be calculated only by applying the charging time and the resistance value of the resistor R, so that the calculation logic is simple and easy to implement.
It should be noted that, since the voltage at two ends of the capacitor C to be measured does not increase linearly during the charging process, the longer the charging time is, the slower the voltage increases; therefore, the smaller the time units included in the charging time, the larger the voltage change value between two adjacent time units, the easier the errors caused by voltage measurement, signal transmission time difference and other reasons are reduced, and the more accurate the capacitance value calculation result is. Therefore, it is preferable that the voltage threshold at the stop timing is a voltage value corresponding to the charging time of one time unit, that is, the stop voltage threshold is set to 0.63Vu.
Fig. 2 is a schematic structural diagram of another capacitance measuring device according to an embodiment of the present invention. Referring to fig. 2, on the basis of the above embodiments, optionally, the capacitance measurement device further includes: the display module 150 is connected to the control module 130 and is powered by the power module 140, and optionally, the power supply voltage required by the display module 150 is the same as that required by the control module 130. The display module 130 (e.g. 1602 screen) is configured to display the capacitance value of the measured capacitor C, so that a worker can clearly and quickly obtain the capacitance value result. Alternatively, the display module 150 may be a touch screen, and may send control information to the control module 130 in addition to displaying information, thereby improving the controllability of the measuring apparatus. Alternatively, the display module 150 and the control module 130 may perform signal transmission through universal asynchronous receiving and transmitting signals.
With continued reference to fig. 2, on the basis of the above embodiments, optionally, a 7.62 mm-pitch socket may be provided on the table surface of the test bench 110 to fix the measured capacitance C. Optionally, the test bench 110 further includes: a discharge switch 113 and a discharge circuit 114; the discharging switch 113 is connected between the measured capacitor C and the discharging circuit 114, and the discharging circuit 114 is used for discharging the measured capacitor C when the discharging switch 113 is closed. Alternatively, the discharge switch 113 may be in the form of a button; the discharge circuit 114 may be formed of a resistor of a suitable size so that the discharge circuit is simple in structure and easy to implement. The embodiment adds a discharging loop based on the above embodiments to facilitate the next measurement or ensure that the worker safely removes the capacitor C to be measured.
With continued reference to fig. 2, on the basis of the above embodiments, optionally, the selection circuit 121 includes: a test voltage selection unit 1211 and a span selection and output unit 1212.
Wherein the test voltage selection unit 1211 includes a power supply terminal, a voltage status signal terminal, and at least two output terminals (three output terminals are shown here by way of example); the power terminal of the test voltage selection unit 1211 is connected to the power module 140, and the voltage status signal terminal is connected to the control module 130; the test voltage selecting unit 1211 is configured to select a test voltage according to the rated voltage of the tested capacitor C, transmit a voltage status signal to the control module 130, and output the test voltage from a corresponding output terminal. The span select and output unit 1212 includes a start signal terminal, a span status signal terminal, an output terminal, and at least two input terminals; at least two input ends of the range selection and output unit 1212 are connected with at least two output ends of the test voltage selection unit 1211 in a one-to-one correspondence manner, a starting signal end and a range state signal end are both connected with the control module 130, and the output ends are connected with the resistor R; the range selection and output unit 1212 is configured to select a test range according to the rated capacitance of the tested capacitor C, transmit a range status signal to the control module 130, and perform constant current output according to the test range and a start measurement signal output by the control module 130. Wherein the test voltage selecting unit 1211 corresponds to a power supply of the range selecting and outputting unit 1212; the magnitude of the output current of the span select and output unit 1212 is related to the resistance value R1 of the resistor R.
Next, the structures that the test voltage selecting unit 1211 and the span selecting and outputting unit 1212 may have are described, but are not limiting to the present invention.
On the basis of the above embodiments, optionally, the test voltage selecting unit 1211 includes: a first selection switch and a voltage selection circuit; the first selection switch is connected with a voltage selection circuit, and the voltage selection circuit is used for selecting the output test voltage. Alternatively, the first selection switch may be a multi-terminal selection switch, and the voltage selection circuit may include a plurality of voltage conversion devices (such as a low dropout linear regulator model LM 2940); the number of terminals of the first selection switch except the fixed end is larger than or equal to the number of the voltage conversion devices. The fixed end of the first selection switch is connected with Direct Current (DC) power supply voltage (such as 36V), the other terminals are connected with the voltage conversion devices in a one-to-one correspondence manner, and the redundant terminals are used for standby; the output terminals of the respective voltage converting means together constitute the output terminal of the test voltage selecting unit 1211. In the test voltage selecting unit 1211 provided in this embodiment, the output voltages of the voltage converting devices are different, and the first selecting switch may select which voltage converting device is used to output according to the rated voltage of the capacitor C to be tested.
Based on the above embodiments, optionally, the span selection and output unit 1212 includes: a second selection switch and a range selection circuit; the second selection switch is connected with a range selection circuit, and the range selection circuit is used for selecting a test range. Optionally, the second selection switch is a multi-terminal selection switch, and the fixed end of the second selection switch is connected with the resistor R; the plurality of input terminals of the span select circuit constitute input terminals of the span select and output unit 1212, and the span select circuit may have a plurality of output terminals through which the output current is output when the second select switch is connected to a certain output terminal of the span select circuit.
With continued reference to fig. 2, based on the above embodiments, optionally, the control module 130 includes: a control unit 131, a first isolation unit 132, and a second isolation unit 133.
Wherein the control unit 131 includes a first end and a second end, and the control unit 131 is a core unit in the control module 130, and is used for timing and calculating; the first isolation unit 132 includes a first end and a second end, the first end of the first isolation unit 132 is connected to the first end of the control unit 131, and the second end is connected to the selection module 120; the second isolation unit 133 includes a first end and a second end, the first end of the second isolation unit 133 is connected to the second end of the control unit 131, and the second end is connected to the start button 111 and the voltage measurement unit 112. The first isolation unit 132 and the second isolation unit 133 are provided to substantially protect the control unit 131 from damage to the control unit 131 due to serial input of signals such as a large voltage.
Illustratively, the first isolation unit 132 and the second isolation unit 133 may each be a photo-coupling device (e.g., model number PC847 or HCNR200, etc.). Note that, in the first isolation unit 132, the second end may include a plurality of terminals, and all terminals connected to the selection module 120 in the first isolation unit 132 are collectively referred to herein as the second end. Similarly, all terminals of the second isolation unit 133 connected to the test bench 110 are collectively referred to as a second terminal.
With continued reference to fig. 2, optionally, the power module 140 includes, based on the above embodiments: the low dropout linear regulator 141 (for example, model LM 2940), the low dropout linear regulator 141 includes an input terminal and an output terminal, the input terminal is connected to the direct current supply voltage DC, and the output terminal is connected to the control module 130 and the display module 150. The direct current supply voltage DC directly supplies power to the selection module 120; the low dropout linear regulator 141 is configured to step down the direct current supply voltage DC and supply power to the control module 130 and the display module 150; to meet the power supply requirements of different modules.
The embodiment of the invention also provides a capacitance measuring method which is realized by adopting the capacitance measuring device provided by any embodiment of the invention, and has corresponding beneficial effects. Fig. 3 is a schematic flow chart of a capacitance measurement method according to an embodiment of the present invention. Referring to fig. 3, the capacitance measurement method includes the steps of:
s110, the selection module selects the sizes of the test voltage and the output current according to the rated parameters of the tested capacitor.
The selection module can select the test voltage according to the rated voltage of the tested capacitor, select the test range according to the rated capacitance of the tested capacitor, and transmit the relevant state information such as the test voltage, the test range and the like to the control module. The output current is related to the test voltage, the test range and the resistance of the resistor in the selection module.
S120, the control module outputs a start measurement signal according to the received start measurement signal output by the start button.
The control module can communicate with the outside through the isolation unit so as to protect the control module from being influenced by external interference signals as much as possible.
S130, a selection circuit in the selection module receives a starting measurement signal, and constant current output is carried out through a resistor to charge a capacitor to be tested; meanwhile, a voltage measuring unit in the test bench measures the voltage at two ends of the measured capacitor.
The selection circuit may include a test voltage selection unit and a span selection and output unit. The test voltage selecting unit is used for selecting test voltage according to rated voltage of the tested capacitor, transmitting a voltage state signal to the control module and outputting the test voltage from the corresponding output end. The measuring range selecting and outputting unit is used for selecting a testing measuring range according to the rated capacitance of the tested capacitor, transmitting a measuring range state signal to the control module, and performing constant current output according to the testing range and a starting measuring signal output by the control module. The test voltage selection unit is equivalent to a power supply of the range selection and output unit; the range selection and the magnitude of the output current of the output unit are related to the resistance value of the resistor.
And S140, the control module counts the charging time of the tested capacitor, and calculates the capacitance value of the tested capacitor according to the voltage at two ends of the tested capacitor, the charging time and the resistance value of the resistor.
The control module can calculate the capacitance value of the measured capacitor according to the RC constant calculation formula. Optionally, the resistor is a high-precision resistor to ensure accuracy of capacitance measurement.
Fig. 4 is a flow chart of another capacitance measurement method according to an embodiment of the invention. The capacitance measuring method will be specifically described with reference to fig. 4, but the present invention is not limited thereto. Referring to fig. 4, optionally, the capacitance measurement method includes the steps of:
s210, the test voltage selecting unit selects test voltage according to rated voltage of the tested capacitor and transmits a voltage state signal to the control module, and the measuring range selecting and outputting unit selects test measuring range according to rated capacitance of the tested capacitor and transmits a measuring range state signal to the control module.
S220, the control module sets calculation parameters according to the voltage state signals and the range control signals.
The calculation parameters may include a sequence of voltage values across the measured capacitor when the charging time reaches different time units.
S230, outputting a start measurement signal by a start button.
S240, the control module outputs a start measurement signal according to the start measurement signal, and starts timing when the start measurement signal is output.
If the influence of the signal transmission time is ignored, the control module can start timing when receiving the start measurement signal, but start timing when outputting the start measurement signal can make the measurement result more accurate. Optionally, the control module may further start timing after a preset delay after outputting the start measurement signal, where the preset delay is from when the control module outputs the start measurement signal, and the processing and outputting of the selection module are performed until the measured capacitor starts to be charged, so that the calculation result is more accurate. However, the above method is complex, and the preset delay is not easy to estimate, so the control module may start timing when the voltage value of the received measured capacitor starts to be different from 0 after sending the start measurement signal. In summary, the condition for starting timing by the control module may be selected according to the actual situation, and since the distance between the modules in the capacitance measurement device is shorter, the influence of the signal transmission time on the result is generally negligible.
S250, the selection module receives a starting measurement signal, and constant current output is carried out through a resistor to charge a capacitor to be measured; meanwhile, a voltage measuring unit in the test bench measures the voltage at two ends of the measured capacitor.
And S260, stopping timing when the voltage at two ends of the tested capacitor reaches a preset threshold value by the control module.
The preset threshold value may be a voltage value that should be reached by the measured capacitor after the charging process of N time units. Optionally, since the voltage at the two ends of the capacitor to be measured can theoretically reach 0.99 times the full-charge voltage value after five time units are charged, if the charging is continued, the voltage value is not easy to distinguish from the voltage value when the capacitor is charged in the previous time unit, so that N can be limited to be an integer greater than 0 and less than 6.
S270, the control module calculates the capacitance value of the tested capacitor according to the charging time and the resistance value of the resistor.
S280, the display module displays the capacitance value of the tested capacitor.
Preferably, the preset threshold is set to be 0.63 times of the full-charge voltage value of the capacitor to be measured; this is because the voltage across the capacitor under test does not increase linearly during the charging process, but increases more slowly the longer the charging time is; therefore, the smaller the time units included in the charging time, the larger the voltage change value between two adjacent time units, the easier the errors caused by voltage measurement, signal transmission time difference and other reasons are reduced, and the more accurate the capacitance value calculation result is. Therefore, the preset threshold is preferably a voltage value corresponding to charging to one time unit.
At this time, S270 includes: the control module divides the charging time by the resistance value of the resistor to obtain the capacitance value of the tested capacitor. The calculation process is simple and easy to realize.
Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.
Claims (8)
1. A capacitance measuring device, comprising:
a test stand including a start button and a voltage measurement unit; the start button is used for outputting a start measurement signal; the voltage measuring unit is used for measuring the voltages at two ends of the measured capacitor;
the selection module comprises a selection circuit and a resistor, and the resistor is respectively connected with the selection circuit and the test bench; the selection module is used for selecting the sizes of the test voltage and the output current according to the rated parameters of the tested capacitor and transmitting the output current to the tested capacitor through the resistor;
the control module is respectively connected with the start button, the voltage measurement unit and the selection circuit; the control module is used for starting measurement according to the starting measurement signal, timing the charging time of the measured capacitor, and calculating the capacitance value of the measured capacitor according to the voltage at two ends of the measured capacitor, the charging time and the resistance value of the resistor;
the power supply module is respectively connected with the control module and the selection module and is used for supplying power to the control module and the selection module;
wherein the selection circuit includes: the test voltage selection unit comprises a power supply end, a voltage state signal end and at least two output ends; the power end of the test voltage selection unit is connected with the power module, and the voltage state signal end of the test voltage selection unit is connected with the control module; the test voltage selecting unit is used for selecting a test voltage according to the rated voltage of the tested capacitor and outputting the test voltage from a corresponding output end; the measuring range selecting and outputting unit comprises a starting signal end, a measuring range state signal end, an output end and at least two input ends; at least two input ends of the range selection and output unit are connected with at least two output ends of the test voltage selection unit in a one-to-one correspondence manner, a starting signal end and a range state signal end of the range selection and output unit are both connected with the control module, and an output end of the range selection and output unit is connected with the resistor; the measuring range selecting and outputting unit is used for selecting a testing measuring range according to the rated capacitance of the tested capacitor and outputting constant current according to the testing range and a starting measuring signal output by the control module;
the test voltage selection unit further includes: a first selection switch and a voltage selection circuit; the first selection switch is connected with the voltage selection circuit, and the voltage selection circuit is used for selecting the output test voltage;
the range selection and output unit further includes: a second selection switch and a range selection circuit; the second selection switch is connected with the range selection circuit, and the range selection circuit is used for selecting the test range.
2. The capacitance measuring device according to claim 1, further comprising: and the display module is connected with the control module and used for displaying the capacitance value of the tested capacitor.
3. The capacitance measuring device of claim 1, wherein the test stand further comprises: a discharge switch and a discharge circuit; the discharging switch is connected between the tested capacitor and the discharging circuit, and the discharging circuit is used for discharging the tested capacitor.
4. The capacitance measuring device according to claim 1, wherein the power supply module includes:
the low dropout linear voltage regulator comprises an input end and an output end, wherein the input end of the low dropout linear voltage regulator is connected with direct current supply voltage, the output end of the low dropout linear voltage regulator is connected with the control module, and the low dropout linear voltage regulator is used for carrying out step-down processing on the direct current supply voltage and supplying power to the control module.
5. The capacitance measuring device of claim 1, wherein the control module comprises:
a control unit including a first end and a second end;
the first isolation unit comprises a first end and a second end, the first end of the first isolation unit is connected with the first end of the control unit, and the second end of the first isolation unit is connected with the selection module;
the second isolation unit comprises a first end and a second end, the first end of the second isolation unit is connected with the second end of the control unit, and the second end of the second isolation unit is connected with the start button and the voltage measurement unit.
6. A capacitance measuring method, characterized in that a capacitance measuring device according to any one of claims 1 to 5 is employed, the capacitance measuring method comprising:
the selection module selects the sizes of the test voltage and the output current according to the rated parameters of the tested capacitor;
the control module outputs a start measurement signal according to the received start measurement signal output by the start button;
a selection circuit in the selection module receives the starting measurement signal, and constant current output is carried out through a resistor to charge the tested capacitor; simultaneously, a voltage measuring unit in the test bench measures the voltages at two ends of the tested capacitor;
the control module counts the charging time of the tested capacitor and calculates the capacitance value of the tested capacitor according to the voltage at two ends of the tested capacitor, the charging time and the resistance value of the resistor.
7. The method of claim 6, wherein the control module counts a charging time of the measured capacitor and calculates a capacitance value of the measured capacitor according to a voltage across the measured capacitor, the charging time, and a resistance value of the resistor, comprising:
the control module starts timing when outputting the starting measurement signal;
the control module stops timing when the voltage at two ends of the tested capacitor reaches a preset threshold value;
and the control module calculates the capacitance value of the tested capacitor according to the charging time and the resistance value of the resistor.
8. The capacitance measurement method according to claim 7, wherein the preset threshold value is 0.63 times the full-power voltage value of the measured capacitance;
the calculating the capacitance value of the measured capacitor according to the charging time and the resistance value of the resistor comprises the following steps:
dividing the charging time by the resistance value of the resistor to obtain the capacitance value of the tested capacitor.
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| CN102129145A (en) * | 2010-01-12 | 2011-07-20 | 马克西姆综合产品公司 | Micro electro-me-chanical systems driver with a capacitance measuring circuit |
| CN105425050A (en) * | 2015-12-17 | 2016-03-23 | 河源广工大协同创新研究院 | Farad meter for ultrahigh capacitance detection |
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| CN107843786A (en) * | 2017-10-31 | 2018-03-27 | 迈普通信技术股份有限公司 | A kind of voltage tolerant Auto-Test System and method |
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| CN103091562A (en) * | 2011-11-08 | 2013-05-08 | 鸿富锦精密工业（深圳）有限公司 | Capacitance capacity measurement circuit |
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| CN102129145A (en) * | 2010-01-12 | 2011-07-20 | 马克西姆综合产品公司 | Micro electro-me-chanical systems driver with a capacitance measuring circuit |
| CN105425050A (en) * | 2015-12-17 | 2016-03-23 | 河源广工大协同创新研究院 | Farad meter for ultrahigh capacitance detection |
| CN105974202A (en) * | 2016-06-21 | 2016-09-28 | 北京华峰测控技术有限公司 | Micro-capacitance reference measurement circuit with multiple measuring ranges and measurement method thereof |
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