JP4249448B2 - Capacitance meter calibration method, calibration standard capacity box, capacitance measurement method, capacitance measurement box and capacitance meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a capacitance meter calibration method and a capacitance measurement method, and more particularly to a zero adjustment and gain adjustment method for a capacitance meter that measures a minute capacitance.
[0002]
[Prior art]
In order to calibrate a capacitance meter that measures capacitance, a standard capacitor with a known capacitance is used.
[0003]
As a specific conventional method, for example, a shield box containing a standard capacitor and a capacitance meter are connected with a coaxial cable, and the capacitance of the standard capacitor is measured and calibrated. At this time, one end of the standard capacitor is connected to the GND (ground) of the capacitance meter, and a coaxial connector attached to the shield box (housing) or shield box in order to shield the intrusion of disturbance noise into the shield box. Unnecessary parts such as the shield part are also connected to GND.
[0004]
[Problems to be solved by the invention]
However, in such a method, a large error occurs for a minute capacitance of 1 pF or less, and accurate calibration is difficult. This is because the capacitance (floating capacitance) generated between the coaxial cable core wire and the housing, or between the coaxial cable core wire and the shield part or shield box of the coaxial connector is added and measured, resulting in an error.
[0005]
As a countermeasure, for example, first, measurement is performed with no standard capacitor connected, and the obtained capacitance value is set to the zero point. Next, measurement is performed with the standard capacitor connected, and the gain (sensitivity) is adjusted. The method is taken.
[0006]
However, even with this method, if the measurement environment changes, such as when the cable connecting the standard capacitor and the capacitance meter is replaced with a cable of a different length or the cable shape changes, the zero point will be There is a problem that it needs to be calibrated again. In addition, it is necessary to create a state in which only the standard capacitor is excluded from the actual measurement state, and for all other objects (measurement environment) except the standard capacitor, both at zero adjustment and at gain adjustment. , Accompanied by difficulties such as having to maintain a completely identical state.
[0007]
For example, in a calibration method that takes a zero point without connecting a shield box containing a standard capacitor to the capacitance meter and adjusts the gain with the shield box connected, the standard is used for gain adjustment. The capacity of the entire shield box containing the capacitor is detected, and there is a problem that calibration using only the capacity of the standard capacitor is not possible.
[0008]
Therefore, the present invention has been made in view of such a situation, and is a method for calibrating a capacity meter using a shield box with a built-in standard capacitor, and the shield box and the capacity meter are connected. To provide a calibration method for a capacity meter that can perform accurate calibration using only the capacity of the standard capacitor in the shield box without being affected by the cable to be used or the capacity of the shield box. Objective.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a calibration method for a capacitance meter according to the present invention includes connecting one end of a standard capacitor to a signal input terminal of the capacitance meter and connecting the other end of the standard capacitor to the same potential as the signal input terminal. A connection step of connecting to a guard voltage output terminal for generating a voltage of 0, and a zero adjustment step of performing zero adjustment of the capacitance meter in a connection state by the connection step.
[0010]
That is, one end of the standard capacitor is connected to the signal input terminal of the capacitance meter, and the capacitance is measured in a state where the guard potential having the same potential as the signal input terminal is applied to the other end, and the zero point is taken. Therefore, although the standard capacitor is still connected to the signal input terminal, both ends of the standard capacitor are at the same potential, so the standard capacitor capacity is not detected and the standard capacitor is removed. Zero point is measured.
[0011]
Further, the calibration method of the capacitance meter is further configured to change the connection destination of the other end of the standard capacitor from the guard voltage output terminal to the reference voltage terminal of the capacitance meter following the zero adjustment step. A connection change step for changing the connection and a gain adjustment step for adjusting the gain of the capacitance meter in the connection state after the connection change by the connection change step may be included.
[0012]
That is, after performing zero adjustment, after changing the connection state in the normal capacitance measurement, that is, after changing the connection so that the standard capacitor is connected between the signal input terminal and the reference voltage terminal of the capacitance meter, Adjust the gain. The reference voltage terminal is a terminal connected to the ground of the capacitance meter or a predetermined potential. Here, the predetermined potential refers to any one of a certain reference potential, a predetermined DC potential, a ground potential, or a floating state, and an optimum one is selected according to the embodiment.
[0013]
At this time, the standard capacitor is stored in an electrically insulated state in a shield box to which at least two coaxial connectors are attached, and both ends thereof are connected to the center electrodes of the two coaxial connectors, respectively. The shield portions of the two coaxial connectors are electrically connected to the casing of the shield box. In the connecting step, the casing of the shield box is further connected to the guard voltage output terminal, and one end of the standard capacitor and the signal input terminal of the capacitance meter are connected by a coaxial cable whose core wire is covered with a shield member. Keep it.
[0014]
As a result, a guard potential having the same potential as that of the core wire is applied to the shield member of the coaxial cable connected to the signal input terminal of the capacitance meter, and stray capacitance therebetween is not detected as a measurement error. . Since the guard potential is also applied to the casing of the shield box, the stray capacitance of the shield box is not detected. Therefore, accurate gain adjustment using only the capacity of the standard capacitor is possible.
[0015]
The connection change in the connection change step may be performed using a changeover switch fixedly attached to the shield box. Similarly, you may perform using the changeover switch attached to the changeover box connected to the position inserted between a shield box and a capacity meter. Further, it may be automated by a switching circuit built in the capacity meter.
[0016]
Further, the present invention can be realized as a standard capacity box for calibration used for the characteristic calibration as described above. That is, a shield box, two coaxial connectors attached to the shield box and having a shield part electrically connected to the shield box, and a case terminal for electrically connecting to the case of the shield box Also, it can be realized as a standard capacity box for calibration comprising a standard capacitor having both ends connected to the center electrodes of the two coaxial connectors while being housed in the shield box in an electrically insulated state. At this time, it is preferable that both ends of the standard capacitor and the center electrode of the two coaxial connectors are connected by a coaxial cable whose core wire is covered with a shield member connected to the shield portion of the coaxial connector.
[0017]
Furthermore, the present invention can also be realized as a capacity meter that automatically executes the characteristic calibration procedure as described above under program control. That is, a signal input terminal and a reference voltage terminal for connecting a capacitor to be measured, a guard voltage output terminal for generating a voltage having the same potential as the signal input terminal, and a standard capacitor having one end connected to the signal input terminal A calibration means for performing calibration using the calibration means, wherein the calibration means performs zero adjustment after connecting the other end of the standard capacitor to the guard voltage output terminal, and connects to the other end of the standard capacitor. Can be realized as a capacitance meter that performs gain adjustment after changing from the guard voltage output terminal to the reference voltage terminal.
[0018]
The zero adjustment and gain adjustment described above can be applied not only to calibration of a capacitance meter but also to capacitance measurement of a capacitor to be measured whose capacitance is unknown. In other words, when performing capacitance measurement with a calibrated capacitance meter, perform zero adjustment and gain adjustment of the capacitor to be measured (in this case, determination of the capacitance value by capacitance measurement) using the same procedure as described above. Thus, the accurate capacitance value of the capacitor to be measured can be measured with a capacitance meter.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1A is an external view of a calibration standard capacity box 1 used for calibration of a capacity meter according to the present embodiment, and FIG. 1B is a schematic circuit diagram of the calibration standard capacity box 1. It is. As shown in FIG. 1 (a), the calibration standard capacity box 1 has three connection terminals (first coaxial connector 2; 1) on the side surface of a casing (shield box) 8 containing a standard capacitor 7 with a known capacity. A box to which the second coaxial connector 3 and the case terminal 4) are attached.
[0020]
As shown in FIG. 1B, the first coaxial connector 2 is a connector for connecting a coaxial cable, and is connected to one end of the standard capacitor 7 via the first coaxial cable 5. That is, the center electrode 2a of the first coaxial connector 2 is connected to one end of the standard capacitor 7 via the core 5a of the first coaxial cable 5, and the shield portion 2b of the first coaxial connector 2 is connected to the first coaxial cable 2. 5 is connected to the shield 5 b and the housing 8. The shield 5b of the first coaxial cable 5 covers the core wire 5a so that the core wire 5a is not exposed, but the other end (the end close to the standard capacitor 7) is electrically open, or the standard capacitor 7 Connected to the case.
[0021]
Similarly, the second coaxial connector 3 is a connector for connecting a coaxial cable, and is connected to the other end of the standard capacitor 7 via the second coaxial cable 6. That is, the center electrode 3a of the second coaxial connector 3 is connected to one end of the standard capacitor 7 via the core 6a of the second coaxial cable 6, and the shield portion 3b of the second coaxial connector 3 is connected to the second coaxial cable 3. 6 shield 6b and housing 8 are connected. The shield 6b of the second coaxial cable 6 covers the core wire 6a so that the core wire 6a is not exposed, but the other end (the end close to the standard capacitor 7) is electrically open or the standard capacitor 7 It may be connected to the case.
[0022]
The case terminal 4 is a terminal electrically connected to the housing 8. This is because the housing 8 and all the parts connected to the housing 8, that is, the shield portion 2b of the first coaxial connector 2, the shield portion 3b of the second coaxial connector 3, the shield 5b of the first coaxial cable 5, and This is a terminal for determining the potential of the shield 6b of the second coaxial cable 6 (applying from the outside).
[0023]
As described above, the standard capacitor 7 is fixed in a state where both ends thereof are connected to the center electrode 2a of the first coaxial connector 2 and the center electrode 3a of the second coaxial connector 3, respectively, and are insulated from the housing 8 and the like. ing.
[0024]
FIG. 2 shows an example of a circuit diagram of a capacitance meter to be calibrated in the present embodiment. The capacitance meter 10 includes an AC voltage generator 11 that generates an AC voltage, a resistor (R1) 12, a resistor (R2) 13, a first operational amplifier 14, a detection resistor (R3) 15, and a second operational amplifier 16. In addition, it has three types of connection terminals (ground terminal 25, signal input terminal 26, guard potential output terminals 27a and 27b) for connection to the calibration standard capacitance box 1 and the capacitor 17 to be measured. , And a signal input terminal 26, and a voltage corresponding to the capacitance is output from the signal output terminal 20 as a detection signal.
[0025]
The guard potential output terminals 27a and 27b are terminals that output a voltage (guard voltage) having the same potential as that of the signal input terminal 26, and prevent stray capacitance generated between the core wire and the shield of the coaxial cable from being detected. Among these, one of the guard potential output terminals 27a is a screw terminal used for connecting to the case terminal 4 of the calibration standard capacity box 1 with a single-wire cable or the like, and the other The guard potential output terminal 27b is a coaxial connector for connecting to the second coaxial connector 3 of the calibration standard capacity box 1 with a coaxial cable at the time of calibration (when the zero point is taken). Moreover, both the ground terminal 25 and the signal input terminal 26 are comprised by the coaxial connector for connecting a coaxial cable. A guard voltage is applied to the shield portion of the coaxial connector constituting the signal input terminal 26 and the shield wire (dotted line in the figure) connected to the shield portion. Further, the shield part of the coaxial connector constituting the two terminals 25 and 27b and the shield wire (dotted line in the figure) connected to the shield part here are in a float state and are connected to each other via a cable. The potential is determined by (the calibration standard capacity box 1 or the like).
[0026]
The AC voltage generator 11 has one end connected to the ground and generates a constant AC voltage (voltage Vin, angular frequency ω) from the other end (output terminal). The first operational amplifier 14 and the second operational amplifier 16 are voltage amplifiers having extremely high input impedance and open loop gain. The non-inverting input terminal of the first operational amplifier 14 is connected to the ground, and the detection resistor 15, the second operational amplifier 16 and the resistor (R2) 13 are connected in series in this order to the negative feedback path, and the inverting amplification. The circuit is configured. The second operational amplifier 16 constitutes a voltage follower having a voltage gain of 1 so that almost all of the current flowing through the measured capacitor 17 connected to the signal input terminal 26 flows through the detection resistor 15. It fulfills the function of generating a guard voltage from its output terminal.
[0027]
The operation of the capacity meter 10 configured as described above is as follows.
When attention is paid to the inverting amplifier circuit composed of the resistor (R1) 12, the resistor (R2) 13, the first operational amplifier 14 and the like, when the voltage at the output terminal 22 of the second operational amplifier 16 is V2,
Vin / R1 = -V2 / R2
Holds. Therefore, the output voltage V2 of the second operational amplifier 16 is
V2 =-(R2 / R1) · Vin (Formula 1)
It becomes. Further, since the second operational amplifier 16 constitutes a voltage follower and both of its input terminals are in an immediate short state, its input voltage (voltage of the non-inverting input terminal 21) V1 is
V1 = V2
=-(R2 / R1) · Vin (Formula 2)
It becomes.
[0028]
Now, assuming that the capacitor to be measured (capacitance Cs) 17 is connected between the signal input terminal 26 and the ground terminal 25 and the current flowing through the detection resistor 15 toward the capacitor to be measured 17 is i, the second operational amplifier Since the input impedance of 16 is very high, all of the current i flows to the capacitor 17 to be measured, so the voltage V1 at the non-inverting input terminal 21 of the second operational amplifier 16 is i · (1 / jωCs), The voltage Vout of the detection signal output from the signal output terminal 20 is
Vout = i · R3 + V1
= (1 + jωCs · R3) · V1 (Formula 3)
It becomes. Substituting V1 represented by the above equation 2 into this equation 3,
Vout =-(1 + jωCs · R3) · (R2 / R1) · Vin (Formula 4)
Is obtained.
[0029]
As can be seen from Equation 4, the voltage Vout of the detection signal output from the signal output terminal 20 of the capacitance meter 10 includes an AC component proportional to the capacitance Cs of the capacitor 17 to be measured. Therefore, the capacitance Cs is specified by performing various signal processing on the voltage Vout.
[0030]
Next, a procedure for calibrating the capacity meter 10 shown in FIG. 2 using the calibration standard capacity box 1 shown in FIG. 1 will be described.
[0031]
FIG. 3 is a flowchart showing the calibration procedure. Here, four steps are shown. First, one end of the standard capacitor 7 in the calibration standard capacitance box 1 is connected to the signal input terminal 26 of the capacitance meter 10, and the other end of the standard capacitor 7 is connected to the guard potential output terminal 27 b of the capacitance meter 10. The case terminal 4 is connected to the guard potential output terminal 27a of the capacitance meter 10 (Step 1). Specifically, the first coaxial connector 2 of the calibration standard capacity box 1 and the signal input terminal 26 of the capacity meter 10 are connected by a coaxial cable, and the second coaxial connector 3 of the calibration standard capacity box 1 and the capacity meter 10 are connected. The guard potential output terminal 27b is connected by a coaxial cable, and the case terminal 4 of the calibration standard capacity box 1 and the guard potential output terminal 27a of the capacity meter 10 are connected by a single wire cable or the like. As a result, both ends of the standard capacitor 7 may be connected to the signal input terminal 26 and the guard potential, and the shield case (the casing 8 of the calibration standard capacity box 1) and the shield portion of each cable may be connected to the guard potential.
[0032]
Subsequently, in this connected state, the capacity meter 10 takes a zero point (Step 2). That is, in this state, the measurement by the capacitance meter 10 is executed, and the offset adjustment of the capacitance meter 10 is performed so that the obtained measurement value (capacitance value) is zero (farad). For example, in the case of a capacity meter incorporating a digital processing circuit such as a CPU, a calibration formula y = a · x + b that relates the measured value x and the displayed value y so that the measured value at this time is displayed as zero farad. Adjust the offset value b.
[0033]
In the measurement at this step, one end of the standard capacitor 7 in the calibration standard capacitance box 1 is connected to the signal input terminal 26 of the capacitance meter 10, but the other end of the standard capacitor 7 is connected. Since a guard potential is applied to both ends of the standard capacitor 7, both ends of the standard capacitor 7 are held at the same potential, and this capacitance is not detected by the capacitance meter 10.
[0034]
Next, the connection of the other end of the standard capacitor 7 in the calibration standard capacitance box 1 is switched from the guard potential output terminal 27b of the capacitance meter 10 to the ground terminal 25 (Step 3). Specifically, for example, at the guard potential output terminal 27b of the capacity meter 10 connected to the second coaxial connector 3 of the calibration standard capacity box 1, the connector of the coaxial cable is removed and the connector is connected to the ground of the capacity meter 10. Connect to terminal 25.
[0035]
As a result, the standard capacitor 7 in the calibration standard capacity box 1 is connected in a normal measurement state, that is, between the signal input terminal 26 and the ground terminal 25 of the capacity meter 10. The other connection states, that is, the connection relationship between the first coaxial connector 2 and the case terminal 4 of the calibration standard capacity box 1 and the capacity meter 10 are left as they are.
[0036]
Finally, in this connected state, the gain is adjusted by the capacity meter 10 (Step 4). That is, in this state, measurement by the capacitance meter 10 is executed, and gain (sensitivity) adjustment of the capacitance meter 10 is performed so that the obtained measurement value (capacitance value) matches the capacitance value of the standard capacitor 7. For example, in the case of a capacity meter incorporating a digital processing circuit as described above, the proportionality coefficient a in the calibration equation y = a · x + b that relates the measured value x and the display value y is adjusted.
[0037]
In the measurement at this step, all the capacitances between the signal input terminal 26 and the ground terminal 25 of the capacitance meter 10 are measured, but the shield of the coaxial cable connected to the signal input terminal 26 of the capacitance meter 10 is measured. Is applied with a guard potential via the shield portion 2b of the first coaxial connector 2 of the calibration standard capacity box 1, and since the core wire and the shield are at the same potential, the stray capacitance between them is added. There is no end. The method for preventing the stray capacitance due to such a guard ring from being detected includes the first coaxial cable 5 (between the core wire 5a and the shield 5b) in the calibration standard capacitance box 1 and the core wire 5a of the first coaxial cable 5. The same applies to the case 8 and the housing 8.
[0038]
Therefore, the measured value obtained in such a connection state corresponds to the capacity of only the standard capacitor 7 that does not include the stray capacitance of the coaxial cable or the standard capacity box 1 for calibration. Calibration with high accuracy using only a specific capacitance value, for example, calibration for a minute capacitance of 1 pF or less is possible. Then, after taking the zero point, the work necessary to start gain adjustment is only to change the connection destination of one coaxial cable. Therefore, troublesome work such as attaching and removing only the standard capacitor 7 is unnecessary.
[0039]
As mentioned above, although the calibration method of the capacity meter concerning the present invention was explained based on an embodiment, the present invention is not limited to this embodiment.
[0040]
For example, in this embodiment, when shifting from zero adjustment to gain adjustment, the coaxial cable is replaced, but instead, this may be realized by a changeover switch. Specifically, in place of the calibration standard capacity box 1 shown in FIG. 1, it is attached to the calibration standard capacity box 30 shown in the external view of FIG. 4 (a) and the schematic circuit diagram of FIG. 4 (b). The changeover switch 31 may be used for switching. According to the calibration standard capacity box 30, the first coaxial connector 2, the second coaxial connector 3 and the case terminal 4 of the calibration standard capacity box 30, the signal input terminal 26 of the capacity meter 10, the ground terminal 25, and the guard potential output. Since one end 7b of the standard capacitor 7 can be connected to either the ground terminal 25 or the guard potential output terminal 27a of the capacitance meter 10 by simply switching the changeover switch 31 with the terminals 27a connected to each other. The zero adjustment and the gain adjustment can be performed continuously without changing the.
[0041]
Similarly, instead of attaching a changeover switch to the calibration standard capacity box, an independent changeover box may be provided to switch the connection destination of one end of the standard capacitor 7. FIG. 5A is a diagram showing the appearance of such a switching box 35 (here, a diagram including the calibration standard capacity box 1), and FIG. 5B is a schematic circuit diagram of the switching box 35. It is. This switching box 35 is used by being connected to a position inserted in the middle of the cable connecting the second coaxial connector 3 of the calibration standard capacity box 1 shown in FIG. 1 and the ground terminal 25 of the capacity meter 10. Switching between connecting the center electrode of the coaxial connector connected to the second coaxial connector 3 of the calibration standard capacity box 1 to the center electrode of the coaxial connector connected to the ground terminal 25 of the capacitance meter 10 or its shield part A switch 36 is provided. Even with such a method using the switching box 35, zero adjustment and gain adjustment can be performed continuously without changing the cable.
[0042]
Furthermore, a circuit corresponding to the switching circuit shown in FIG. And about the switching, an operator may operate manually, and the capacity meter 10 may be equipped with a function of automatically executing the four steps shown in FIG. 3 in series by program control or the like. .
[0043]
In addition, a circuit corresponding to the calibration standard capacity box shown in FIG. 1 and the switching circuit shown in FIG. And about the switching, an operator may operate manually, and the capacity meter 10 may be equipped with a function of automatically executing the four steps shown in FIG. 3 in series by program control or the like. .
[0044]
On the other hand, in FIG. 1B, a guard potential is applied to the shield portion of the coaxial cable connected to one of the connectors 2 and 3, and a guard potential is applied to 2b, 3b, 5b, 6b and 8. good. In this case, the case terminal 4 may be left unconnected. In FIG. 1 (b), 2b and 3b are electrically connected to 8, but 2b and 3b are insulated from 8, and a guard potential is applied to the shield portion of the coaxial cable connected to the terminals 2 and 3, thereby 2b, 3b and 5b. , 6b may be applied with a guard potential.
[0045]
In the present embodiment, the standard capacitor and the capacitor to be measured are connected between the signal input terminal 26 and the ground terminal 25 of the capacitance meter 10. A terminal connected to a predetermined potential biased by a certain potential may be used. Since the capacitance meter 10 shown in FIG. 2 measures the capacitance based on the AC signal from the AC voltage generator 11, if the potential is AC zero, the predetermined potential can be used as the reference potential. Because.
[0046]
In the present embodiment, the portion to which the guard potential is applied is exposed, such as the case 8 of the calibration standard capacity box 1. However, the entire calibration standard capacity box 1 is insulated from the case 8. It may be housed in a shielded box, or a coaxial cable or coaxial connector may have a double or triple coaxial structure, and the outermost conductive portion may be floated or grounded.
[0047]
Further, the calibration method of the capacitance meter shown in the present embodiment can be used not only for calibration of the capacitance meter but also as a method for measuring the capacitance of the capacitor to be measured. Specifically, as shown in FIG. 6, a capacitance measuring box 91 is prepared in which the standard capacitor 7 in the calibration standard capacitance box 1 shown in FIG. Then, the capacity measuring box 91 is connected to the capacity meter 10 calibrated in Steps 1 to 4 shown in FIG. 3, and the capacity is measured in the same steps as in FIG. In other words, as shown in FIG. 6, with both ends of the measured capacitor 97 connected to the signal input terminal and the guard potential, and the housing 8 connected to the guard potential (Step 5), after taking the zero point (Step 6) ) In the state where both ends of the measured capacitor 97 are connected to the signal input terminal and the ground, and the housing 8 is connected to the guard potential (Step 7), the capacitance of the measured capacitor 97 is measured (Step 8).
[0048]
In the last step (capacitance measurement; Step 8), the final measurement value may be determined by a process such as multiplying the actual measurement value by the coefficient obtained by calibration. FIG. 7 is a diagram showing an example of actual measurement values obtained by such a process. Here, as a result of performing the calibration shown in FIG. 3 using the standard capacitor 7 having a “reference value” of 0.9598 pF, 0.67355 pF was obtained as the “measurement value”. It is determined to be 1.4250. In such a calibration state, the measured capacitor 97 of 1.0261 pF was measured by the measurement method shown in FIG. 6, and as a result, a measurement value of 1.0267 pF was obtained. As described above, by applying the zero adjustment and gain adjustment according to the present invention to calibration and actual measurement in capacity measurement, accurate capacity measurement can be performed.
[0049]
Such a capacity measuring box 91 is different from the calibration standard capacity box 1 in that the capacity of the built-in capacitor is unknown or known, and has the structure shown in FIGS. The point that can be built in the capacity meter 10 is common to the standard capacity box 1 for calibration. For example, a circuit corresponding to the switching circuit shown in FIG. 5B may be incorporated in the capacitance meter 10 and used for both calibration and measurement.
[0050]
【The invention's effect】
As is clear from the above description, the calibration method of the capacitance meter according to the present invention is such that one end of the standard capacitor housed in the shield box is connected to the signal input terminal of the capacitance meter, and the other end of the standard capacitor is connected to the signal Perform zero adjustment of the capacitance meter while connected to the guard voltage output terminal that generates a voltage of the same potential as the input terminal, and then connect the other end of the standard capacitor from the guard voltage output terminal to the reference voltage of the capacitance meter. After changing the connection so that it is changed to the terminal, the gain of the capacity meter is adjusted. During these adjustments, a guard voltage is applied to the shield box.
[0051]
As a result, even though one end of the standard capacitor remains connected to the signal input terminal of the capacitance meter, the standard capacitor capacity was not detected by the guard ring technique during zero adjustment, and the standard capacitor was removed. Since the capacity is measured in a state equal to the state and the zero point is taken, accurate zero adjustment can be performed with a simple operation.
[0052]
In gain adjustment, since the guard potential is applied to the shield of the coaxial cable connecting the shield box and the capacity meter, and to the casing of the shield box, the stray capacitance generated in the coaxial cable and the seal box is included. The gain is adjusted by the capacity of only the standard capacitor, and the capacity meter is calibrated with high accuracy.
[0053]
Moreover, by applying such a calibration method to the capacitance measurement of a capacitor to be measured whose capacitance is unknown, the accuracy is improved not only for calibration but also for capacitance measurement.
[0054]
In this way, according to the present invention, accurate calibration using only the capacitance of the standard capacitor in the shield box is not affected by the influence of the cable connecting the shield box and the capacity meter, or the capacitance of the shield box. In addition, it is possible to perform accurate capacitance measurement. In particular, the technical value of the present invention is extremely high as a highly accurate calibration method and capacitance measurement for a microcapacitor that measures a minute capacitance of 1 pF or less.
[Brief description of the drawings]
FIG. 1 (a) is an external view of a calibration standard capacity box used for calibration of a capacity meter in an embodiment of the present invention, and FIG. 1 (b) is a schematic circuit diagram of the calibration standard capacity box. is there.
FIG. 2 shows an example of a circuit diagram of a capacity meter to be calibrated.
FIG. 3 is a flowchart showing the calibration procedure.
4A is an external view of a calibration standard capacity box according to a modified example of the calibration standard capacity box shown in FIG. 1, and FIG. 4B is a schematic circuit diagram thereof.
5A is an external view of a switching box used together with the calibration standard capacity box shown in FIG. 1, and FIG. 5B is a schematic circuit diagram of the switching box.
FIG. 6 is a flowchart showing a procedure for measuring the capacitance of a capacitor to be measured.
FIG. 7 is a diagram illustrating an example of actual measurement values in calibration using a standard capacitor and capacitance measurement of a capacitor to be measured.
[Explanation of symbols]
1, 30 Standard capacity box for calibration
2 First coaxial connector
2a, 3a Center electrode
2b, 3b Shield part
3 Second coaxial connector
4 Case terminal
5, 6 Coaxial cable
5a, 6a core wire
5b, 6b Shield
6 Coaxial cable
7 Standard capacitor
8 Case
10 Capacity meter
11 AC voltage generator
12, 13 resistance
14, 16 operational amplifier
15 Resistance for detection
17 Capacitor to be measured
20 Signal output terminal
21 Non-inverting input terminal
22 Output terminal
25 Ground terminal
26 Signal input terminal
27a, 27b Guard potential output terminals
31, 36 selector switch
91 Capacity measurement box
97 Capacitor to be measured

Claims (17)

A capacitance meter calibration method for measuring capacitance between a reference voltage terminal connected to ground or a predetermined potential and a signal input terminal ,
A connection step of connecting one end of a standard capacitor to a signal input terminal of a capacitance meter and connecting the other end of the standard capacitor to a guard voltage output terminal that generates a voltage having the same potential as the signal input terminal;
And a zero adjustment step of performing zero adjustment of the capacitance meter in the connection state in the connection step. The capacitance meter calibration method further includes:
Following the zero adjustment step, a connection change step for changing the connection so that the connection destination of the other end of the standard capacitor is changed from the guard voltage output terminal to the reference voltage terminal of the capacitance meter,
The method according to claim 1, further comprising: a gain adjustment step of performing gain adjustment of the capacitance meter in a connection state after the connection change by the connection change step. The standard capacitor is housed in a shield box to which at least two coaxial connectors are attached in an electrically insulated state, and both ends thereof are respectively connected to center electrodes of the two coaxial connectors,
The shield portions of the two coaxial connectors are electrically connected to the casing of the shield box, and further include a sub-step of connecting the casing of the shield box to the guard voltage output terminal. The calibration method for a capacitance meter according to claim 1 or 2, wherein the one end and the signal input terminal of the capacitance meter are connected by a coaxial cable whose core wire is covered with a shield member. 4. The method of calibrating a capacity meter according to claim 1, wherein the connection change in the connection change step is performed by using a changeover switch fixedly attached to the shield box. The connection change in the connection change step is:
The capacitance according to any one of claims 1 to 3, wherein the capacitance is performed using a changeover switch attached to a changeover box connected to a position inserted between the shield box and the capacitance meter. How to calibrate the meter. 4. The method for calibrating a capacity meter according to claim 1, wherein the connection change in the connection change step is performed by a switching circuit built in the capacity meter. A standard capacity box for calibration used for calibration of a capacity meter,
A shield box,
Two coaxial connectors attached to the shield box and having a shield portion electrically connected to the shield box;
A housing terminal for electrical connection with the housing of the shield box;
A standard capacity box for calibration, comprising: a standard capacitor housed in the shield box in an electrically insulated state and having both ends connected to respective center electrodes of the two coaxial connectors. The both ends of the standard capacitor and the center electrode of the two coaxial connectors are connected by a coaxial cable having a core wire covered with a shield member connected to a shield portion of the coaxial connector. Standard capacity box for calibration as described. The said calibration standard capacity box is further provided with the changeover switch which switches the connecting point of the end of the said standard capacitor from the center electrode of the said coaxial connector to the housing | casing of the said shield box. Standard capacity box for calibration. A capacitance meter for measuring capacitance,
A signal input terminal and a reference voltage terminal for connecting a capacitor to be measured; and
A guard voltage output terminal for generating a voltage having the same potential as the signal input terminal;
Calibration means for performing calibration using a standard capacitor having one end connected to the signal input terminal,
The reference voltage terminal is connected to the capacitance meter ground or a predetermined potential,
The calibration means includes
After connecting the other end of the standard capacitor to the guard voltage output terminal, zero adjustment is performed, and after changing the connection destination of the other end of the standard capacitor from the guard voltage output terminal to the reference voltage terminal, gain adjustment is performed. The capacity meter characterized by performing. The capacity meter according to claim 10, comprising the calibration standard capacity box according to claim 7. A method of measuring the capacitance of a capacitor to be measured using a capacitance meter that measures the capacitance between a reference voltage terminal connected to ground or a predetermined potential and a signal input terminal ,
Connecting one end of the capacitor to be measured to a signal input terminal of a capacitance meter, and connecting the other end of the capacitor to be measured to a guard voltage output terminal that generates a voltage having the same potential as the signal input terminal;
And a zero adjustment step of performing zero adjustment of the capacitance meter in the connection state in the connection step. The method for measuring the capacitance further includes:
Following the zero adjustment step, a connection changing step for changing the connection so that the connection destination of the other end of the capacitor to be measured is changed from the guard voltage output terminal to the reference voltage terminal of the capacitance meter;
The capacitance measuring method according to claim 12, further comprising: a capacitance measuring step of measuring a capacitance of the capacitor to be measured in a connection state after the connection is changed by the connection changing step. The method for measuring the capacitance further includes:
Prior to the connection step, one end of a standard capacitor was connected to the signal input terminal of the capacitance meter, and the other end of the standard capacitor was connected to a guard voltage output terminal that generates a voltage having the same potential as the signal input terminal. In the state, after performing the zero adjustment of the capacitance meter, in a state where the connection is changed so that the connection destination of the other end of the standard capacitor is changed from the guard voltage output terminal to the reference voltage terminal of the capacitance meter. The method for measuring capacitance according to claim 12, further comprising a calibration step of performing gain adjustment of the capacitance meter. A capacitance measuring box used to measure the capacitance of a capacitor to be measured,
A shield box,
Two coaxial connectors attached to the shield box and having a shield portion electrically connected to the shield box;
A housing terminal for electrical connection with the housing of the shield box;
A capacitance measuring box comprising: a capacitor to be measured that is housed in the shield box in an electrically insulated state, and that is connected to both ends of each of the center electrodes of the two coaxial connectors. A capacitance meter for measuring capacitance,
A signal input terminal and a reference voltage terminal for connecting a capacitor to be measured;
A guard voltage output terminal for generating a voltage having the same potential as the signal input terminal;
Measuring means for measuring the capacitance using a measured capacitor connected at one end to the signal input terminal;
The reference voltage terminal is connected to the capacitance meter ground or a predetermined potential,
The measuring means includes
After connecting the other end of the measured capacitor to the guard voltage output terminal, zero adjustment is performed, and after changing the connection destination of the other end of the standard capacitor from the guard voltage output terminal to the reference voltage terminal, A capacitance meter that measures the capacitance of a standard capacitor. The capacity measuring box according to claim 15 is provided. The capacity meter according to claim 16 characterized by things.

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