JPH01105179A - Induced voltage discriminating device - Google Patents

Abstract

PURPOSE:To easily discriminate whether a measured voltage is an induced voltage or actual voltage by inserting an external resistance which is connected and disconnected through a switch in parallel to the input resistance of a digital voltmeter. CONSTITUTION:The external resistance 1 (resistance value R) is inserted into the input side of the digital voltmeter in parallel to the input resistance 3 (resistance value Ri). Here, the resistance value R<<Ri. The external resistance 1 can be connected and disconnected through the switch 2 to vary the input resistance optionally. Then the electric power of the induced voltage is extremely small and the internal resistance is extremely large, so the input resistance is varied by turning on and off the switch 2 and then it is decided that the measured value is the induced voltage when the indication value of the digital voltmeter varies or the actually found voltage of an intense current circuit when not.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an apparatus for determining induced voltage in measured values in an AC voltage measuring instrument having a high input resistance such as a digital voltmeter.

(b) Conventional technology Digital voltmeters have extremely high input resistance in order to accurately measure the voltage of high internal resistance circuits with as little disturbance as possible. Note that the digital voltmeters currently on the market have the same manual resistance for each range. Therefore, when measuring the voltage of a high current outlet with a long electrical line in a factory etc. using a digital voltmeter,
Even if you measure the induced voltage induced in a long electric wire due to the extremely high input resistance, and even if you learn the measurement range, the current commercially available digital voltmeters will not measure the same value because the input resistance is the same between the measurement ranges. Indicates the indicated value.

Therefore, it is not possible to determine whether the measured voltage is an induced voltage or an actually desired voltage. In fact, in my experience, if you measure the voltage on the automatic control wiring of a production line at a manufacturing factory using a digital voltmeter with an input resistance of 10MΩ, you may get an indicated value of approximately 100V. Also, since the human resistance is the same for each range, the same indicated value is obtained.

In this case, if the control voltage is 10 (IV), it is impossible to determine whether a control signal is coming or an induced voltage. Therefore, if you have no choice but to connect a light bulb of about 20 W and turn it on, a control signal will come. If the voltmeter does not light up, it is determined to be an induced voltage.However, if the internal resistance is low, such as a 1mA voltmeter, the induced voltage will not be measured, and there is no such inconvenience.However, each Digital voltmeters, which have the same human resistance as the range and an extremely high input resistance, are extremely effective in measuring the voltage of high internal resistance circuits such as transistor circuits, and the appeal of their extremely high input resistance is hard to dismiss. However, because of this feature, it has the disadvantage of measuring induced voltage.In addition, the indicated value may be disturbed due to the influence of noise.Therefore, in factories, etc., high current circuits with long electrical lines are currently not available on the market. It is not suitable to measure voltage with a digital voltmeter.

(1) Problems to be Solved by the Invention The purpose of the invention is to easily determine whether a measured voltage is an induced voltage or an actually desired voltage, while taking advantage of the extremely high input resistance of digital voltmeters.

(d) Means for Solving the Problems An example in which the present invention is applied to a voltmeter with high input resistance, such as a digital voltmeter, will be described below with reference to the drawings.

As shown in Figure 1, at the input part of the digital voltmeter, an external resistor R (Ri) is inserted in parallel with the input resistor Ri, and the external resistor R can be turned on and off at will by the SW, so that the input resistance can be changed arbitrarily. This will be explained using the equivalent circuit of FIG. 2 as follows.

The voltage of a strong current circuit having a long electrical line is E1, the internal resistance is r, the indicated value of the digital voltmeter is V, the input resistance is Ri, and the external resistance is R. Further, it is assumed that the external resistor R can be turned on and off as desired by a switch SW.

Note that the power of the induced voltage is extremely small and the internal resistance is extremely high.

In the equivalent circuit of FIG. 2, the indicated value V of the digital voltmeter is expressed by the following equation.

When the SW is OFF, the indicated value V of the digital voltmeter is V. When the SW is ON, R(Ri, When the indicated value V of the digital voltmeter is V, then = Ri, E. (E) Effect When the voltage E of a strong current circuit with a long electric line is an induced voltage, the power of the induced voltage is extremely small and the internal resistance is extremely high, so R(Ri(r), V, (V).

The power of the strong current circuit is extremely large compared to the power of the induced voltage, and the internal resistance is extremely small, so r(R(Ri), v, = V.

Therefore, if the indicated value of the digital voltmeter changes by turning the switch on and off and changing the input resistance, the measured value will be the induced voltage, and if it does not change, the measured value will be the voltage actually sought by the strong current circuit, making it difficult to determine the measured value. can.

(f) Effects of the Invention As explained above, this invention provides an external resistance R (Ri) connected in parallel to the input resistance of a conventional digital voltmeter.
By inserting the external resistor R and making it possible to arbitrarily change the input resistance by turning on and off the external resistor R using the SW, it is possible to determine whether the measured value is an induced voltage or the actual voltage required by the strong current circuit by operating the SW. can be easily determined.

Also, when the input resistance is low, it becomes less susceptible to the effects of induced noise.In this way, it is easy to determine whether the measured value is an induced voltage or the voltage actually required by the strong current circuit.
Low input resistance makes it less susceptible to induced noise (this improves measurement efficiency and measurement accuracy).

First, electric shock accidents can be prevented by easily determining whether the voltage is induced or not. Note that since there are two unknowns, the internal resistance r1 electromotive force E of the circuit under test, which is an unknown, can be found by calculation.

[Brief explanation of the drawing]

FIG. 1 shows an example in which the present invention is applied to a high input resistance voltmeter such as a digital voltmeter, and FIG. 2 shows both circuits thereof. 1: External resistance R 2: External switch SW 3: Digital voltmeter with input resistance Ri and measured value V 4: Circuit under test with internal resistance r1 and electromotive force E 5: Input resistance of digital voltmeter Ri 6: Circuit under test Internal resistance r 7: Electromotive force E of the circuit under test

Claims (1)

[Claims] In voltage measuring instruments etc. with high input resistance, in order to reduce the high input resistance to low input resistance, the input resistance R is set at the input section.
An induced voltage discriminator that can arbitrarily change the input resistance by inserting an external resistor R such that R≪Ri in parallel with i, and allowing the external resistor R to be turned on and off arbitrarily by a switch.