JPH063463B2 - Electricity detector for signal source - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electric quantity detecting device for a signal source.

(Prior art) A load whose resistance value changes, such as an operating value settling circuit of a protective relay or a measurement range switching circuit of a measuring instrument,
When connecting to a signal source with internal resistance, it is generally the first
A circuit configuration as shown is used.

In the figure, 1 is a signal source having an internal resistance R _s , such as an instrument transformer (PT) and its internal resistance, or a current transformer and its internal resistance. Reference numeral 2 _denotes a load resistance composed of a variable resistance VR whose resistance value changes and an invariable resistance R _n whose resistance value does not change, and corresponds to the above-mentioned setting circuit of the protective relay. Reference numeral 3 is a detection device for detecting the quantity of electricity (voltage or current) of the signal source 1, and specifically, for example, a non-inverting amplifier circuit with an amplification factor of 1 can be considered.

In such a circuit configuration, if the output voltage of the detection device 3 is V _o , Is given. (However, I _S is the current of the signal source.) In this formula, when R _s << VR + R _n holds, V _o
≈I _s · R _s , and the output voltage V _o is approximately proportional to the current I _s . Therefore, as the conventional technique, the load resistance VR +
The R _s, to configure such that R _s "VR + R _n were common to the internal resistance R _s.

However, when the signal source is a constant current source such as a current transformer, the internal resistance R
_{Since s} is relatively large, R _s << VR + R _n may not hold, in which case the output voltage V _o is no longer proportional to the current I _s . Further, since the output voltage V _o is essentially affected by the load resistance VR + R _n , an error occurs in the output voltage V _o .

By the way, as is clear from the Feng-Thevenin theorem or Norton's theorem, it can be seen that an output voltage equal to the signal source voltage can be obtained by adding the internal voltage drop due to the internal resistance of the signal source to the load terminal voltage. Since the internal voltage drop cannot be measured directly, the load terminal voltage cannot be easily corrected.

Therefore, in addition to the terminal voltage of the load, directly measure the load current, or connect a known resistor in series with the load and measure this voltage drop to obtain the load current. A method of adding the internal voltage drop obtained by calculating the product with the resistance value to the terminal voltage of the load can be considered.

(Problems to be solved by the invention) However, in such a method, it is necessary to provide a multiplication circuit and / or a division circuit in addition to the addition circuit, which causes a problem that the circuit configuration becomes complicated.

Therefore, in view of the above points, the present invention provides a voltage accurately proportional to the quantity of electricity of the signal source from the voltage drop (terminal voltage of the load) of the load resistor connected to the signal source having the internal resistance,
With a simple circuit configuration of only the adder circuit,
The purpose is to increase the reliability of this type of circuit.

(Means for Solving the Problem) The present invention provides a signal source having an internal resistance R _s and a variable resistance V
A load resistance in which R and a constant resistance R _n are connected in series is connected, and the total voltage drop (terminal voltage) of the load resistance is connected to this load resistance.
An adder circuit having two input sections for the voltage drop (terminal voltage) V ₂ of V ₁ and R _n is connected.

Then, the circuit constants of the respective input parts of the adder circuit are set to ₁ for the V ₁ input part and R _s / R _n for the V ₂ input part, and V ₁ and V are added to the adder circuit configured as described above. Add ₂ Is calculated.

(Operation) According to this structure, the V ₁ by V ₁ input V
₁ , the V ₂ input section converts V ₂ into V ₂ (R _s / R _n ), and by simply adding this, the effect of the load resistance VR + R _n can be completely removed, and the signal source An output voltage proportional to the amount of electricity can be obtained.

(Embodiment) FIG. 2 shows an embodiment of the present invention. In this embodiment, a current transformer and its secondary resistor as the signal source 10 having an internal resistance R _s and a settling circuit 20 of a protective relay for the load resistances VR and R _n will be described as an example. The load resistance in VR is a variable resistor, R _n is a resistor unchanged.

Reference numeral 30 is a detection device for detecting the current of the signal source 10 and is composed of an adder circuit using an operational amplifier OP.

First, the detection device 30 will be considered. Since the total voltage drop (the terminal voltage of the load) V ₁ due to the resistance VR + R _n and the divided voltage drop V ₂ due to R _n are given to the terminals A and B of the detection device 30, respectively, the output voltage V _o is Becomes

Here, the circuit constants of the adder circuit input section are R ₁ = R ₂ , R ₃ =
When set to (R _n / R _s ) · R ₁ , However, the input voltages V ₁ and V ₂ are Becomes, and if this is substituted into the above formula, Becomes

That is, the input voltage V ₁ is added to the input voltage V ₂ by (R _s / R _n ) ·
It can be understood that the result of adding the converted V ₂ is proportional to the electric quantity (I ₁ · R _s ) of the signal source.

(Effect of the Invention) As described above, according to the present invention, two types of voltages, that is, the total voltage drop of the load (terminal voltage of the load) and the divided voltage drop of the load are simply added by using only the adding circuit. Since it is simple and has a highly reliable circuit configuration, the signal source having an internal resistance produces an output that is accurately proportional to the electric quantity of the signal source without being affected by load fluctuations. .

[Brief description of drawings]

FIG. 1 is an electrical connection diagram for explaining the present invention, and FIG. 2 is an electrical connection diagram showing an embodiment of the device of the present invention. Reference numeral 10 is a signal source, 20 is a load resistance, 30 is a detection device (adding circuit), R _s is an internal resistance, VR and R _n are load resistances, and OP is an operational amplifier.

Claims (1)

[Claims] 1. A signal source having an internal resistance, and a load resistance connected to the signal source, wherein a variable resistance that is a component whose resistance value changes and a constant resistance that is a component whose resistance value does not change are connected in series. It comprises an adder circuit that inputs the total voltage drop based on the load resistance and the voltage drop based on the invariable resistance, and the adder circuit is a circuit of an input unit for the total voltage drop based on the load resistance of the adder circuit. The constant is set to 1, and the circuit constant of the input section of the voltage drop based on the invariable resistance is set to a value obtained by dividing the internal resistance of the signal source by the invariant resistance, and the total voltage drop based on the load resistance and the invariant are set. An electric quantity detecting device for a signal source, characterized in that a voltage drop based on a resistance is added through respective input parts to obtain an output proportional to an electric quantity of the signal source.