JPH0142053Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit element constant measuring device equipped with an offset correction circuit that eliminates the influence of stray capacitance.

Circuit element constant measuring devices for measuring the constants of circuit elements such as resistors, capacitors, and inductors are well known (for example, Japanese Patent Publication No. 50-27741, Japanese Patent Publication No. 53
-9539). Such a measuring device is equipped with an offset correction circuit for eliminating the influence of capacitance distributed on the measuring line. Furthermore, since this capacity changes over time due to factors such as the ambient temperature of the device, it is necessary to re-set the offset correction over time.

The present invention has been devised to eliminate the above-mentioned drawbacks, and is intended to provide a circuit element constant measuring device that automatically performs offset correction each time a device under test is connected.

The figure is a circuit diagram of a circuit element constant measuring device according to an embodiment of the present invention. In the figure, one measurement terminal 11 is one input terminal 15 of the synchronous rectifier 13.
In addition, the other measurement terminal 17 is connected to the other input terminal 21 of the synchronous rectifier 13 via a standard element (resistor) 19. The output terminal of the synchronous rectifier 13 is connected to a calculation circuit 23, as well as an on/off switch 25, a hold capacitor 27, and a high gain amplifier 29 with a sufficiently large input impedance.
It is connected to a voltage holding circuit 31 consisting of. The output terminal of the voltage holding circuit 31 is connected to the transformer 3 via the resistor 34 in the offset control circuit 33.
The intermediate tap 5 is connected to both terminals of the grounded secondary winding via a voltage variable capacitance element 37 and a capacitor 39, respectively. Voltage variable capacitance element 3
7. A common connection point 41 of the capacitor 39 is connected to a common connection point 43 between the measurement terminal 17 and the standard element 19 via a DC blocking capacitor 45. An input terminal 61 connected to the measurement terminal 11 is supplied with an AC voltage e _r from the measurement voltage source 1 . Common connection point 43
has become a virtual ground. The reason for this is also explained in detail in the above-mentioned patent publication, but it can be abbreviated as follows. The voltage generated at the common connection point 43 is detected by an amplifier with a high amplification degree (for example, an operational amplifier or an AC→DC→AC conversion type amplifier) whose one input terminal is grounded.
amplified. And the output of the amplifier is standard element 1
9 to the other terminal 63 of the measuring terminal 11,
In other words, the common connection point 4
The voltage of No. 3 is controlled to be zero voltage (virtual ground). Also, the transformer 3 is connected between the terminal 61 and the ground.
5 primary windings are connected. In addition, switch 51,
The opening/closing operation of 53 is controlled by a timing circuit 65, and the device under test (here, a capacitor) 6
7 is connected between the successive measurement terminals 11 and 17. Note that the switches 51 and 53 are not necessarily necessary, and may be sufficient as long as they are capable of connecting the device to be measured 67 between the measurement terminals 11 and 17 (for example, by manual operation).

Next, the operation of the above configuration will be explained. First, a correction mode in which switch 25 is closed while switches 51 and 53 are open will be described. In this case terminal 6
The voltage e _x1 at 3 is e _x1 =jωC ₀ ·1/G _r ·e _r (1). here. C ₀ is the stray capacitance value between the measurement terminals 11 and 17, and G _r is the conductance of the standard element 19. That is, since the voltage e _x1 is proportional to the admittance of the stray capacitance, when the voltage e _x1 is rectified by the synchronous rectifier 13 using the voltage e _r (constant) as a reference, a voltage proportional to the stray capacitance value C ₀ is generated.
V _r1 is obtained. This voltage V _r1 is stored in the hold capacitor 27, and an offset control voltage V ₀ corresponding to the voltage V _r1 is generated from the voltage holding circuit 31. The capacitance value of the voltage variable capacitance element 37 changes according to this control voltage V ₀ , and the current supplied through the transformer 35 in the opposite direction to the current of the standard element 19 changes accordingly. In this way, the current flowing through the standard element 19 is controlled to be zero.
The offset control voltage V ₀ continues to be generated from the voltage holding circuit 31 during the next measurement mode.

Next, open switch 25, and switch 5
The measurement mode in which 1 and 53 are closed will be explained.
In this case as well, the current flowing through the device under test 67 and the current flowing through the standard device 19 are controlled to be equal, and the influence of the stray capacitance C ₀ is corrected in the correction mode described above, so the voltage at the terminal 63 is
For e _x2 , the following relationship holds true: e _x2 = jωC _X・1/G _r・e _r (2). Here, C _X is the device under test 6
The capacitance value is 7. Since the stray capacitance C ₀ is not included in equation (2), if the voltage e _x2 is synchronously rectified with the voltage e _r as a reference, the voltage V _r2 corresponding to the measured capacitance value _C
is obtained. Therefore, the measured capacitance value C _X is determined by the calculating circuit 23 based on this voltage V _r2 .

Open the switches 51 and 53 again, then close the switch 25 to enter the correction mode. After the correction operation, the next device to be measured is connected and a measurement operation is performed.

As detailed above, according to the present invention, the circuit element constants can be measured by removing the influence of stray capacitance each time, especially when measuring by changing the device under test, for example, when testing multiple capacitors in succession. It is extremely effective in practical use.

[Brief explanation of drawings]

The figure is a circuit diagram of a circuit element constant measuring device according to an embodiment of the present invention, in which 1: measurement voltage source, 13: synchronous rectifier, 19: standard element, 23: calculation circuit, 31:
Voltage holding circuit, 33: Offset control circuit, 6
7: Element to be measured.

Claims (1)

[Claims for Utility Model Registration] (1) The same current is supplied to the series circuit of the device under test and the standard device, and the common connection point of the series circuit is controlled to become a virtual ground point, A device for performing synchronous rectification based on the voltage across an element and the voltage across the standard element, and measuring circuit constants of the element under test according to a synchronous rectification output signal, comprising: a switch connected to the output of the synchronous rectification circuit; a hold circuit connected to the switch, which closes the switch and holds the synchronous rectified output signal during a period when the device under test is not connected between measurement terminals; Accordingly, a circuit element constant measuring device comprising an offset correction circuit comprising a control circuit that supplies a current having an opposite phase to the current flowing through the standard element to the common connection point. (2) The control circuit connects both terminals of the secondary winding of the transformer, which has a primary winding connected in parallel to both measurement terminals, to which the intermediate tap on the secondary side is grounded, and the holding circuit. A circuit element constant comprising an offset correction circuit according to claim 1 of the utility model registration claim, comprising a voltage variable capacitance element and a capacitor respectively connected between a second common connection point to which an output signal is supplied from the offset correction circuit. measuring device.