JPH0653779A - Dc signal extract method in ac signal and method for eliminating the dc signal - Google Patents

Abstract

PURPOSE:To extract a DC signal included in an AC signal and to eliminate the DC signal through digital calculation not relying on the hardware configuration. CONSTITUTION:A sample-and-hold circuit 1 samples one period or its integer number of multiple of the period of an AC signal V (=vmsinomegat+Vdc) by a time division being equal N-division (N is an even number being 2 or over). Sampled data are converted into digital data Vi (i=1-N) by an A/D converter circuit 2 of a next stage, the data are given to a CPU 3. The data are subject to arithmetic operation in equation I in the CPU 3 and a DC signal Vdc is obtained. The DC signal Vdc is extracted from the AC signal V including the DC signal, and the DC signal Vdc is cancelled from the AC signal V by the calculation of Vi-Vdc, that is, by subtracting the DC signal Vdc from the data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for extracting a DC signal contained in an AC signal by digital processing and a method for removing the DC signal from the AC signal.

[0002]

2. Description of the Related Art For example, when measuring each parameter of a circuit element with an LCR meter, an AC voltage applied to the circuit element and an AC current detected through the circuit element are synchronously rectified. If a DC signal is included in the signal, it may appear as an error in a later calculation.

Therefore, conventionally, a DC signal is removed by adding an offset cancel circuit to the offset adjustment terminal of an operational amplifier (op-amp), or by interposing a capacitor in the preceding stage of the operational amplifier, so-called AC coupling of the capacitor. I am trying to do it.

[0004]

However, in any case, since it depends on the hardware, the final fine adjustment by hand is required.

In addition to this, in the case of using a capacitor, a CR circuit is assembled in combination with a resistor R,
The stabilization time of the circuit as a whole and the input / output impedance of the operational amplifier may be affected.

[0006]

The present invention has been made in view of such conventional circumstances, and the structural features thereof are included in an AC signal as described in claim 1. In the method of extracting a DC signal, N (N is an even number of 2 or more) data Vi (i = 1 to N) sampled at a predetermined time interval from one cycle of the AC signal and digitally converted. Is a processing means (CP
U)

[Equation 2] Is to extract the DC signal Vdc.

Further, in claim 2, the data V
By subtracting the DC signal Vdc from each of i (i = 1 to N), the DC signal contained therein is removed from the AC signal.

[0008]

In general, an AC voltage including a DC voltage is expressed by the following equation: V = Vmsinωt + Vdc (Vm is the maximum value). In the equation, V
Msinωt is an AC component, and Vdc is a DC component.

One cycle of this signal is sampled at predetermined time intervals to obtain N pieces of data, and the A / D converted data is defined as Vi (i = 1 to N). Due to the symmetry of the waveform, the AC component becomes "0" when the data for one period is added.

Therefore,

[Equation 3] Then, the DC voltage Vdc is obtained. By the way,

[Equation 4] Is equivalent to

The DC voltage Vdc is converted from each data Vi.
The DC voltage contained in the AC voltage is canceled by subtracting each of these.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In carrying out the present invention, as shown in FIG. 1, a sample hold circuit 1, an A / D conversion circuit 2, and a central processing unit (CPU) 3 as a calculation means are used.

As shown in FIG. 2, the sample and hold circuit 1 has an AC signal V (= Vmsinωt + Vd).
One cycle of c) is sampled at N equal time intervals (N is an even number of 2 or more). In this example, the sampling target is one cycle, but sampling may be performed over an integral multiple of that cycle.

The sampled data is A /
Digital data Vi (i = N) is generated by the D conversion circuit 2.
After being converted to, it is given to the CPU 3.

Each data is stored in the CPU 3.

[Equation 5] The DC signal Vdc is calculated by the following equation.

In this way, the DC signal Vdc contained therein is extracted from the AC signal V, which is Vi-Vd.
c (i = 1 to N), that is, DC signal Vdc from each data
To subtract the DC signal Vdc from the AC signal V.
Can be canceled.

[0017]

As described above, according to the present invention, it is possible to extract a DC signal contained in an AC signal by digital operation without using a hardware configuration, and
The DC signal can be removed.

[Brief description of drawings]

FIG. 1 is a circuit diagram applied to the present invention.

FIG. 2 is a waveform diagram for explaining the present invention.

[Explanation of symbols]

 1 Sample and hold circuit 2 A / D conversion circuit 3 CPU

Claims (2)

[Claims] 1. A method for extracting a DC signal contained therein from an AC signal, wherein N (N is 2) samples of at least one period of the AC signal at predetermined time intervals and digitally converted. The above even-numbered data Vi (i = 1 to N) is calculated by the arithmetic processing means (CPU) as follows: A method for extracting a DC signal in an AC signal, which comprises performing the following calculation to extract the DC signal Vdc. 2. An AC signal characterized by removing the DC signal contained therein from the AC signal by subtracting the DC signal Vdc from each of the data Vi (i = 1 to N). DC signal removal method.