JPH01193659A - Circuit for digital resistance measuring apparatus - Google Patents

Abstract

PURPOSE:To achieve stability, by inserting a current-voltage converter in series into a resistance to be measured to apply a voltage generated in the resistance and a voltage generated in an output of the converter respectively to an analog input of an A/D converter and a reference voltage input. CONSTITUTION:Two auxiliary earth electrodes C and P are set for a ground electrode E to be measured and electrodes E and P are connected to an analog input terminal of an A/D converter 7 via a desired amplifier/rectifier circuit M. One end of a primary coil of a current transformer A is connected to the electrode E and the other end thereof to the side of a power source while a secondary coil thereof connected to a reference input terminal of the converter 7 via the amplifier/rectifier circuit N. A digital output is shown on a digital display device 8 as ground resistance value from a voltage applied to the analog input of the converter 7 and a voltage applied to a reference terminal. This permits stable measurement without use of a constant current circuit.

Description

[Detailed description of the invention] (a) Industrial application field This invention provides a measuring device that uses a dry cell battery or the like as a power source for measurement, and whose measured value is not affected by a drop in battery voltage. It is something that you are trying to gain.

Conventional technology Conventionally, in this type of measuring instrument, a constant current circuit was used to flow a constant current through the resistor R to be measured, and the 1π pressure drop of the resistor R was measured to determine the resistance value. However, this method had a problem with the constant current circuit. That is, during long-term use, changes occurred in the constant current, which caused errors.

1) Problems to be Solved by the Invention The present invention aims to provide a digital resistance measuring device that is stable over a long period of time without using a constant current circuit.

B) Means for Solving the Problems The following describes a circuit in which the present invention is implemented as a ground resistance measuring device.

In a conventional circuit in which two auxiliary ground electrodes C and P are set for the ground electrode E to be measured and an alternating current is passed through the ground, the ground electrodes E and P are passed through an arbitrary amplifying rectifier circuit M. Connect the analog input terminal of AD converter 7. Also, one end of the primary coil of the current transformer A as a current-voltage converter is connected to the ground electrode E, and the other end is connected to the power supply side, and the secondary coil of the stationery is connected through an arbitrary amplifying rectifier circuit N. It is connected to the reference voltage input terminal of the AD converter 7, and the output terminal of the AD converter 7 is connected to a digital display.

Function: In the above circuit, if the circuit current is I and the ground resistance of the ground electrode E to be measured is R, the voltage applied to the analog input of the AD converter 7 becomes R1, and the voltage applied to the reference voltage terminal of the AD converter 7 becomes R1. The applied voltage is 2I. However, in the above, 1 and 2 are constants.Generally, A having a reference voltage circuit
In a D converter, its digital output is V1, its analog input voltage is V1, its reference voltage is V2, and if it is a constant, then D=In the above equation, V+= K+RI V2=
K21 Null D = Therefore, the value of R can be displayed. Furthermore, the present invention may optionally be applied to ordinary electrical resistance measurement by using a direct current as the measuring current.

(f) Effects of the Invention As explained above, the present invention makes it possible to obtain a more accurate and stable digital resistance measuring instrument by using the conventional method (with some simple improvements).

[Brief explanation of the drawing]

The drawing shows a circuit diagram of a ground resistance measuring device according to an embodiment of the present invention, where A is a current transformer, M and N are arbitrary amplifying rectifier circuits, P, C and E are ground electrode connection terminals, and 4 and 5 are respectively auxiliary ground electrodes, 6 is a ground electrode to be measured, l is an AC generator, 2 is a battery, 3 is a switch, 7 is an AD converter, and 8 is a pretal display.

Claims (1)

[Claims] An arbitrary current-voltage converter A is inserted and connected in series with the resistance to be measured R, and the voltage generated at the resistance to be measured R is added to the analog input of the AD converter 7 via an arbitrary circuit M. A circuit for a digital resistance measuring instrument, characterized in that the circuit includes a circuit in which the voltage generated at the output of the AD converter 7 is applied to the reference voltage input of the AD converter 7 through an arbitrary circuit N.