JPH10104290A - Digital grounding resistance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital grounding resistance measuring device by which the measured value can immediately and directly be read by merely pressing a switch in the measurement of grounding resistance. SOLUTION: In auxiliary grounding poles, P pole and C pole, which are set on the ground substantially on a straight line for a grounding pole E to be measured when grounding resistance is measured, one end of a primary coil of CT3 is connected with the E pole in series, and a voltage of a power supply 1 is supplied to the primary coil of CT3 and C pole through a resistance 6. Then, an output voltage of a secondary coil of CT3 is applied to a reference voltage input end of an integration type AD converter 8 through any rectification circuit 7, and a voltage generated between the P pole and the E pole is applied to an analog voltage input end of the AD converter 8 through any rectification circuit 17. Then, a digital numeric device 9 is connected with an output end of the AD converter 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring instrument for measuring the quality of grounding equipment which is important for security in electric equipment and electric equipment.

[0002]

2. Description of the Related Art Almost all conventional measuring instruments of this type employ a method shown in FIG. In FIG.
Are the earth poles to be measured P and C are auxiliary earthing poles set on the ground with respect to E. Reference numeral 1 denotes an AC power supply for measurement, 2 denotes a rotating type sliding resistor, 3 denotes a CT, 4 denotes a rectifier circuit, and 5 denotes a galvanometer. In this circuit, a current is supplied from the power source 1 and the axis of the sliding resistor 2 is adjusted by turning the axis of the sliding resistor 2 so that the indication of the galvanometer 5 indicates zero. Thus, the ground resistance value of the ground electrode E to be measured was obtained from the pointer provided on the axis and the scale provided therefor.

[0003]

In the conventional method, in the case of a measuring operation, the measuring instrument is first set horizontally, and the resistor is carefully slid and the zero indicating point of the galvanometer is determined. The resistance value was read from the scale indication of the guideline. This work is mostly outdoor work and rainy work. An object of the present invention is to provide a digital earth resistance measuring instrument which can immediately know a measured value by numerical display by simply pushing a switch.

[0004]

In order to solve the above-mentioned problems, first, the sliding resistor, the rectifier circuit, the current detector, etc. of the secondary circuit of the CT in FIG. 2 is applied to a so-called reference voltage input terminal of an integrating AD converter 8 through an optional rectifier circuit 7 as shown in FIG. By pressing a switch button by connecting a digital display 9 of a numerical display to an output terminal of the AD converter 8 via a rectifier circuit 17 and an analog voltage input terminal of the AD converter 8, an immediate input is performed. You can read the measured resistance value.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 2, when a power switch 16 is turned on, a measuring current I flows to the ground through a primary coil of a CT3 and a grounding electrode E to be measured, to a point P, and to a C auxiliary grounding electrode. Then, the current flows back to the power supply 1 through the resistor 6. This CT3 2
The voltage generated in the following coil becomes _V 1 = IK ₁ if _{V 1.} However K ₁ becomes V _{2 =} IR If the measured ground resistance value of constant addition E electrode and R the voltage between point E and point P and V _2.
However, if the input impedance of the rectifier circuit 17 is increased, the influence of the ground resistance of the P pole and the influence of the Hilter capacitor 13 can be neglected. Be Since D is proportional to R, the value of R can be read directly from the display of D by selecting the value of K.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment will be described with reference to FIG. 3. A resistor 12 is connected to an E-pole as a current-voltage converter connected to the E-pole at the auxiliary ground poles P and C with respect to the ground E to be measured set on the ground. The voltage generated at both ends of the resistor 12 is connected to a reference in terminal of an AD converter (using Maxim ICL7116) through an amplifying and rectifying circuit 10 using an operational amplifier (using JRC2904), and then connected to a P pole. And the voltage between the E pole is the operational amplifier (JR
Amplifying and rectifying circuit 11 using C2904 is connected to the analog-in terminal of the AD converter 8, and a digital display 9 is connected to the output of the AD converter.

[0007]

Since the present invention is constructed as described above, it is possible to obtain a grounding resistance measuring device in which the measured value can be read directly by simply pressing the power switch when measuring the grounding resistance.

[Brief description of the drawings]

FIG. 1 is a drawing showing a conventional technique.

FIG. 2 is a diagram showing a circuit according to claim 1;

FIG. 3 is a diagram showing a circuit according to claim 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply 2 Rotating type sliding resistor 3 CT 4 'Rectifier circuit 5 Galvanometer 6 Resistance 7 Rectifier circuit 8 AD converter 9 Display 10 Rectifier circuit 11 Rectifier circuit 12 Resistance 13 Capacitor 14 Battery 15 Electric field 16 Switch 17 Rectifier Circuit 18 switch

Claims (2)

[Claims] 1. As shown in FIG. 2, auxiliary grounding poles P and C are set on the ground substantially in a straight line with respect to a measured grounding pole E to which one end of a primary coil of a CT3 is connected in series. The CT
An AC voltage is applied across one end of the primary coil 3 via a resistor 6. At this time, the voltage generated in the secondary coil of CT3 is applied to an optional rectifier circuit 17 and applied to the reference voltage input terminal of the integrating AD converter 8, and the voltage generated between the P and E poles is applied to an arbitrary rectifier circuit 7. A digital ground resistance measuring instrument for connecting a digital numeral display to an output terminal of the AD converter 8 in addition to an analog voltage input terminal of the AD converter 8 2. The CT according to claim 1, as shown in FIG.
Digital earth resistance measuring instrument that inserts and connects resistor 12 instead of removing 3