JPH0245155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for a measuring instrument that performs a continuity test on an electric circuit.

Checking the electrical wiring in an electrical circuit is the first step in testing equipment. Conventionally, a tester or a DC buzzer has been used to test the continuity of electrical wiring. That is, a tester is used to read the resistance value between two points, and it is determined whether or not the wiring between them is correct. Or, connect the buzzer with the battery connected to 2
Connect between points and judge the wiring condition by whether the buzzer sounds or not.

In the case of this conventional test equipment, the voltage applied between two terminals during measurement is the battery voltage, for example, about 1.5V.

On the other hand, among the electronic components used in devices, integrated circuits (ICs) in particular are becoming more susceptible to electrical shocks, such as voltage and current, as the degree of integration increases.

Therefore, if you conduct a continuity test on an IC circuit using conventional test equipment, the IC may be destroyed due to overvoltage or overcurrent, or even if it does not result in destruction.
There is a flaw in that it degrades the IC and reduces the reliability of the device.

In particular, test equipment consisting only of a battery and a buzzer has a drawback in that the surge voltage caused by the buzzer's inductance can destroy the IC.

There are also devices that combine batteries and buzzers with electrical parts to prevent overvoltage and overcurrent, but the detection resistor, that is, the resistance that stops the buzzer from sounding, is very large at 50Ω to 1KΩ, making it difficult to detect subtle disconnections or poor continuity. The drawback is that it is inaccurate to detect.

There is also a method of determining continuity by measuring the resistance value between two points using a tester, but this method has the drawback of poor workability as the resistance value must be checked each time. .

The present invention is a novel invention that eliminates the above-mentioned defects, and its objectives are (1) to provide a continuity tester that requires less voltage and current applied to an IC circuit and does not deteriorate the IC.

(2) To provide a continuity tester that has a small detection resistance and can accurately judge the continuity state of a circuit.

(3) To provide a continuity tester with good workability.

one of the four sides is composed of a bridge circuit consisting of at least two resistors, a resistor connected in series with the bridge circuit, a differential amplifier, a voltage comparator, and a display means, 2
This is achieved by using both ends of one of the resistors as input terminals.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

1 is an input circuit, 2 is a differential amplifier, 3 is a voltage comparator, 4 is a buzzer, 5 to 11 are resistors, 12 and 13 are input terminals for measuring continuity, 14 and 15 are outputs of the bridge circuit, 16 and 17 are outputs of the differential amplifier, 18 and 19 are transistors forming the differential amplifier, and 20 is a battery.

Connect the two points at which the electrical circuit of the device is to be tested for continuity to the input terminals 12 and 13, measure the resistance between them, amplify the outputs 14 and 15 of the bridge circuit with the differential amplifier 2, and output the output 16 of the differential amplifier 2. , 17 are compared by the voltage comparator 3 to drive the buzzer 4.

Input circuit 1 includes resistor 7, resistor 8, resistors 9 and 11,
Bridge circuit with resistor 10 on four sides and resistors 5 and 6
Therefore, there is an effect that there is little change in the detection resistance value due to a change in the voltage of the battery 20.

The input circuit 1 will be explained using an example of resistance value. Resistors 7, 8, and 10 are 50Ω, resistor 9 is 45Ω, and resistor 11 is 500Ω. When the input terminals 12 and 13 are open, the potential between the outputs 14 and 15 of the bridge circuit is positive on the output 14 side. Input terminal 12,1
When a resistor of 5Ω or less is connected to terminal 3, the potential between outputs 14 and 15 of the bridge circuit becomes negative on the output 14 side, the outputs 16 and 17 of differential amplifier 2 are reversed, the output of voltage comparator 3 is turned on, and buzzer 4 is turned on. sounds.
That is, the resistance values on each side of the bridge circuit are selected so that when the resistance connected to the input terminals 12 and 13 becomes less than the detection resistance value, the polarity of the potential between the outputs 14 and 15 is reversed. Therefore, a highly sensitive continuity tester with a small detection resistance value can be realized. The detection resistance value in this case is 5Ω.

By connecting the resistors 5 and 6 in series to the bridge circuit, the voltage of the battery 20 can be divided and the voltage between both ends of the resistor 11, that is, the input terminals 12 and 13 can be reduced, so the voltage applied to the IC circuit during the continuity test can be reduced. The current flowing through the IC circuit is also limited. When resistors 5 and 6 are 4KΩ and 5KΩ, and the battery voltage is 3V, the voltage when input terminals 12 and 13 are open is 30mV or less, and the current when shorted is 0.4m.
Since it is less than A, it will not deteriorate the IC.
Of course, due to the circuit configuration, no surge voltage or surge current will be applied.

Voltage comparator 3, which operates with one power supply, outputs a comparison voltage.
If it is set to 0V or near the power supply voltage, the error will increase and the operation will become uncertain, but by dividing the series resistance into resistors 5 and 6, it is possible to operate the voltage comparator 3 near the center of the voltage of the battery 20. This makes it possible to improve the accuracy of voltage comparison.

FIG. 2 is a circuit diagram of a second embodiment of the present invention.

22 is an operational amplifier integrated into an IC, 23 is a variable resistor for zero point adjustment, 24 is the output of the operational amplifier 22, 25 and 26 are resistors for creating a reference voltage for the voltage comparator 3, and 27 is a variable resistor for the voltage comparator 3. This is a reference voltage input.

The variable resistor 23 is originally used to adjust the zero point of the operational amplifier 22, but in this embodiment, the voltage comparator 3 is adjusted by moving the zero point of the output 24 and bringing the voltage comparison to the center of the power supply voltage. ensure the operation of

If the variable resistor 23 is adjusted so that the output 24 of the operational amplifier 22 becomes smaller than the reference voltage input 27 when the resistance of the input terminals 12 and 13 exceeds the detection resistance value, the resistance of the input terminals 12 and 13 becomes less than the detection resistance. When this happens, the output 24 becomes higher than the reference voltage input 27, so the output of the voltage comparator 3 turns on and the buzzer 4 sounds.

In the above description, the case where the continuity indicating means is a buzzer has been described, but the present invention is not limited to this, and it goes without saying that the present invention can be similarly implemented with an indicator such as a light emitting diode or a lamp.

As explained above, according to the present invention, one of the four sides is composed of a bridge circuit consisting of at least two resistors, a resistor connected in series with the bridge circuit, a differential amplifier, a voltage comparator, and a display means. ,
By using both ends of one of the two resistors on one side of the bridge circuit as the input terminal, the detection resistance is small, the voltage and current applied to the circuit under test are small, the workability is good, and the reliability of the device is improved. It is possible to realize a continuity tester that does not damage the

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a first embodiment of the present invention;
FIG. 2 is a circuit diagram of a second embodiment of the present invention. 1 is an input circuit, 2 is a differential amplifier, 3 is a voltage comparator, 4 is a buzzer, 5 to 11 are resistors, 12 and 13 are input terminals for measuring continuity, 14 and 15 are outputs of the bridge circuit, 16 and 17 are the outputs of the differential amplifier, 18 and 19 are transistors that constitute the differential amplifier, 20 is a battery, 22 is an IC operational amplifier, 23 is a variable resistor for zero point adjustment, and 24
is the output of the operational amplifier 22, 25 and 26 are resistors for creating a reference voltage of the voltage comparator 3, and 27 is the reference voltage input of the voltage comparator 3.

Claims (1)

[Scope of Claims] 1. The bridge circuit comprises a bridge circuit in which one of the four sides is composed of at least two resistors, a resistor connected in series with the bridge circuit, a differential amplifier, a voltage comparator, and a display means, A continuity tester characterized in that both ends of one of the two resistors on one side are used as input terminals. 2. The continuity tester according to claim 1, wherein the bridge circuit is configured such that the magnitude of the output potential is reversed when the input terminal is open and when a resistance value lower than the detection resistor is connected. 3. The continuity tester according to claim 1, wherein a bias voltage is applied to the output of the differential amplifier when the difference between the input signals is zero. 4. The continuity tester according to claim 1, wherein the resistor connected in series to the bridge circuit is composed of two resistors and is connected to both ends of the bridge circuit. 5 Claim 1 wherein the display means is a buzzer
continuity tester.