Input circuit for an electrical energy meter
First Claim
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1. An input circuit for a meter unit suitable for measuring electrical energy associated with voltage and current signals, the input circuit comprising:
- a voltage sensor receiving the voltage signal, a current sensor receiving the current signal, and respective voltage and current paths for connecting said sensors to respective inputs of the meter unit, the current sensor being in the form of a mutual inductance transformer and the current path including a phase shifting active filter based on an amplifier having two inputs and one output, said amplifier being associated firstly with an AC gain adjusting resistance which is connected upstream from the first input of said amplifier, and secondly with a feedback connection including a feedback capacitance, thereby looping the output of the amplifier back onto the first input thereof, wherein the phase shifting active filter further includes a coupling capacitance connected between the output of the amplifier and the feedback connection.
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Abstract
The invention relates to an input circuit for an electrical energy meter, which circuit has a current path and a voltage path, the current path being associated with a mutual conductance transformer. In order to compensate for the differentiating function of the transformer, but without introduicng interference signals, the current path includes an active filter connected as an integrator and provided with a coupling capacitance suitable for blocking low frequency signals.
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Citations
9 Claims
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1. An input circuit for a meter unit suitable for measuring electrical energy associated with voltage and current signals, the input circuit comprising:
- a voltage sensor receiving the voltage signal, a current sensor receiving the current signal, and respective voltage and current paths for connecting said sensors to respective inputs of the meter unit, the current sensor being in the form of a mutual inductance transformer and the current path including a phase shifting active filter based on an amplifier having two inputs and one output, said amplifier being associated firstly with an AC gain adjusting resistance which is connected upstream from the first input of said amplifier, and secondly with a feedback connection including a feedback capacitance, thereby looping the output of the amplifier back onto the first input thereof, wherein the phase shifting active filter further includes a coupling capacitance connected between the output of the amplifier and the feedback connection.
- View Dependent Claims (2, 3, 4, 5, 6)
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7. An input circuit for a meter unit suitable for measuring electrical energy associated with voltage and current signals, the input circuit comprising;
- a voltage sensor receiving the voltage signal, a current sensor receiving the current signal, and respective voltage and current paths for connecting said sensors to respective inputs of the meter unit, the current sensor being in the form of a mutual inductance transformer and the current path including a phase shifting active filter based on an amplifier having two inputs and one output, said amplifier being associated firstly with an AC gain adjusting resistance which is connected upstream from the first input of said amplifier, and secondly with a feedback connection including a feedback capacitance, thereby looping the output of the amplifier back onto the first input thereof, wherein the phase shifting active filter further includes a coupling capacitance connected to the output of the amplifier upstream from the feedback connection, wherein in order to provide a phase shift of 45°
, the active filter comprises a leakage resistance connected in parallel with the feedback capacitance, said circuit being intended for a reactive electrical energy meter. - View Dependent Claims (8, 9)
- a voltage sensor receiving the voltage signal, a current sensor receiving the current signal, and respective voltage and current paths for connecting said sensors to respective inputs of the meter unit, the current sensor being in the form of a mutual inductance transformer and the current path including a phase shifting active filter based on an amplifier having two inputs and one output, said amplifier being associated firstly with an AC gain adjusting resistance which is connected upstream from the first input of said amplifier, and secondly with a feedback connection including a feedback capacitance, thereby looping the output of the amplifier back onto the first input thereof, wherein the phase shifting active filter further includes a coupling capacitance connected to the output of the amplifier upstream from the feedback connection, wherein in order to provide a phase shift of 45°
Specification