JP2002084191A - Measuring device for electrical signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrical signal measuring device where a reference voltage of an A/D converter is decided by monitoring a peak value of a signal to be measured, for utilizing the resolution of the A/D converter. SOLUTION: An electrical signal measuring device is provided where a signal to be measured is converted into a digital form for various measurements. Here, there are provided and A/D converter comprising a reference voltage terminal for deciding a full scale of an analogue input, a signal pre-processing circuit which normalizes the signal to be measured to an input level of the A/D converter, a reference voltage adjusting means which monitors an output of the A/D converter and adjusts the signal of the reference voltage terminal, so that the peak value of the output is within a predetermined range, a calculation circuit for various calculations with the output of the A/D converter, and a control circuit for controlling the device as a whole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the accuracy of an electric signal measuring instrument. More specifically, the present invention relates to adjusting the reference voltage of an A / D converter in accordance with the state of an input signal. The present invention relates to an electric signal measuring instrument capable of maximizing the resolution of a D converter.

[0002]

2. Description of the Related Art Regarding the configuration of a conventional electric signal measuring instrument,
This will be described with reference to FIG. FIG. 1 shows a configuration of a voltage measuring device as an example of an electric signal measuring device.

In FIG. 1, a signal under test Vin is attenuated by an attenuator 1, normalized by an amplifier 2 to an input level of an A / D converter 3, and then converted to an A / D converter 3.
Is input to

[0004] The A / D converter 3 converts an input signal into a digital value, and converts the output into a digital signal processor (hereinafter referred to as DSP) 6 and a CP via an insulating circuit 5.
Send to U8.

[0005] The DSP 6 uses the output sent from the A / D converter 3 to perform an arithmetic process for calculating an effective value, an average value, and the like of the signal under measurement Vin.

The CPU 8 is a control device for controlling the entire voltage measuring device, and uses the operation result of the DSP 6 and the output sent from the A / D converter 3 based on a user's instruction sent from the operating device 7. Required information is displayed on the display 9.

The CPU 8 sends a range switching instruction to the range control circuit 4, and the range control circuit 4 adjusts the attenuation factor of the attenuator 1 and the amplification factor of the amplifier 2 based on the instruction to switch the range. I do. At this time, the CPU 8 executes the DSP based on the range switching instruction sent to the range control circuit 4.
It goes without saying that the calculation result sent from 6 is subjected to range conversion and the numerical value of the conversion result is displayed on the display 9.

In a conventional voltage measuring device, an input electric signal is converted into a digital signal and a voltage is measured by such a configuration.

[0009]

However, in the conventional electric signal measuring device, the resolution of the A / D converter is not fully utilized, and the measurement required for realizing high-accuracy measurement is required. There has been a problem that an expensive A / D converter having a resolution several times higher than the precision must be used. The reason will be described below.

Normally, the electric signal measuring instrument is provided with a plurality of ranges, and based on the range setting, adjusts the attenuator 1 and the amplifier 2 as described above to thereby measure the signal under test Vi.
n is normalized to the input level of the A / D converter 3 and input to the A / D converter 3.

The general A used for the above applications
As shown in FIG. 5, the / D converter 3 has an input terminal In for inputting an analog signal to be converted into a digital value,
A reference input terminal Vref to which a reference voltage for determining the analog full scale of the A / D converter is input, and an input terminal In
Is provided with an output terminal Out from which a digital value corresponding to the analog signal input to is output.

When an A / D converter having such a configuration is used for an electric signal measuring instrument, for example, an analog signal of the A / D converter is used so that an extremely distorted waveform as shown in FIG. 6 can be accurately measured. Full scale is the normalized A / D converter 3
Of the input level (more precisely, the effective level of the input level).

For example, when a DC signal is measured by an electric signal measuring instrument in which the margin is set to three times, as shown in FIG. The full scale of the converter 3 (between the least significant bit LSB to the most significant bit MSB of the output of the A / D converter 3) has a margin six times the input level of the A / D converter 3. become. For example, in the A / D converter shown in FIG. 5, if the input level of the A / D converter 3 normalized by the attenuator 1 and the amplifier 2 is 1 V, the reference of the A / D converter 3 This is realized by applying a reference voltage of 6 V to the input terminal Vref.

Therefore, in the measurement in this case, FIG.
As shown in (1), when measuring a DC signal, only 1/6 (about 17%) of the resolution of the A / D converter 3 can be used. Also, when measuring a sine wave as shown in FIG. 8B, the peak value of the sine wave is √2 times the effective value, and therefore, ６ × √2 × 2 ≒ 0.47 (1 Therefore, only about 47% can be used.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and determines the reference voltage of the A / D converter by monitoring the peak value of the signal under measurement, thereby maximizing the resolution of the A / D converter. An object of the present invention is to provide an electric signal measuring instrument that can be used.

[0016]

According to the first aspect of the present invention, there is provided an electric signal measuring instrument for digitally converting a signal under measurement and performing various measurements.
An A / D converter having a reference voltage terminal for determining a full scale of an analog input; a signal preprocessing circuit for normalizing the signal under measurement to an input level of the A / D converter; A reference voltage adjusting means for monitoring the output of the A / D converter so as to adjust the signal of the reference voltage terminal so that the peak value of the output falls within a predetermined range; An arithmetic circuit for performing an operation and a control circuit for controlling the entire apparatus are provided.

According to a second aspect of the present invention, in the first aspect of the present invention, the pre-processing circuit includes a signal attenuator and an amplifier, and is configured to perform a plurality of range switching. Is what you do.

According to a third aspect of the present invention, in the first aspect, the reference voltage adjusting means applies a reference voltage specified by the control circuit to a reference voltage terminal of the A / D converter. A D / A converter is provided.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the reference voltage adjusting means includes the A / A
A reference voltage applied to a reference voltage terminal of the A / D converter is adjusted so that a peak value of an output value of the D converter falls within a predetermined range. It is.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the signal pre-processing circuit includes
An automatic range circuit for adjusting the magnitude of a signal to be sent to the D converter within a predetermined range is provided.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of an electric signal measuring device according to the present invention. The point different from the conventional example in the figure is that the reference voltage terminal Vref of the A / D converter 3 is connected to the CPU 8.
And a D / A converter 10 for applying a voltage specified by the D / A converter. The other configuration is the same as that of the conventional example, and thus the same reference numerals are given and the description is omitted.

The operation of the electric signal measuring device of the present invention will be described below with reference to the flowchart shown in FIG.

In FIG. 1, a CPU 8 inputs an output of the A / D converter 3 through an insulating circuit 5 and outputs a signal Vi to be measured.
Monitor the peak value of n. (ST1)

It is determined whether the output of the A / D converter 3 is within a predetermined range. For example, when the peak value of the output of the A / D converter 3 is in a range of 95% (± 2%) with respect to the half scale of the A / D converter 3, ST
The process moves to ST3, and if it is out of this range, the process moves to ST4. (ST2)

The measurement is continued. (ST3)

If the output of the A / D converter 3 is out of the specified range, the CPU 8 adjusts the output to the D / A converter 10 and applies it to the reference terminal VREF of the A / D converter 3. By adjusting the reference voltage, the peak value of the output of the A / D converter 3 is adjusted so as to fall within the specified range.
(ST4)

A re-measurement is performed, and the process returns to ST1. (ST5)

In the electric signal measuring device of the present invention, such an operation is repeated to measure the electric signal.

In the example described above, the voltage applied to the VREF terminal is adjusted so that the peak value of the output signal of the A / D converter 3 is close to 95% of the half scale of the A / D converter 3. For example, when measuring a sine wave as shown in FIG. 3A, the resolution of the A / D converter 3 is set to 9
5% can be utilized, and even when a DC signal is measured as shown in FIG. 3 (b), the A / D conversion is performed according to ×× 0.95 ≒ 0.475 (2). About 48% of the resolution of the detector 3 can be utilized.

That is, in the electric signal measuring device of the present invention, the peak value of the signal to be measured is monitored, and the reference voltage of the A / D converter 3 is adjusted according to the monitored value.
High-precision measurement that makes full use of the resolution of the instrument.

Further, conventionally, the electric signal measuring instrument has an auto-range function for automatically selecting and setting an optimum range according to the magnitude of the signal to be measured, but the electric signal measuring instrument of the present invention has the CPU 8 The S / N ratio (ratio of signal level / noise level) is further improved by installing a program for realizing this auto-range function and automatically selecting the optimum range according to the magnitude of the input signal. High-precision measurement can be performed. The reason is as follows.

As for voltages that can be handled at the electronic circuit level, generally, the higher the handled voltage, the higher the SN ratio and the higher the accuracy of measurement. The concept of range switching (including the auto-range function) used in conventional electric signal measuring instruments is to perform high-precision measurement after increasing the SN ratio of analog signals as much as possible. On the other hand, the electric signal measuring instrument of the present invention does not pay attention to the SN ratio of an analog signal, but performs high-precision measurement by paying attention to the SN ratio and quantization error of the A / D converter itself. Therefore, the conventional auto-range function for performing high-accuracy measurement after increasing the SN ratio of an analog signal and the high-accuracy measurement focusing on the S / N ratio and quantization error of the A / D converter itself are attempted. By combining the functions of the present invention, it is possible to perform high-precision measurement with a higher SN ratio.

The foregoing description has been directed to specific preferred embodiments for the purpose of illustration and illustration of the invention. Therefore, the present invention is not limited to the above-described embodiment, and includes many more modifications without departing from the spirit thereof.
This includes deformation.

For example, the reference voltage terminal V of the A / D converter 3
The means for applying the voltage specified by the CPU 8 to the ref is not limited to the D / A converter 10 described above. For example, a means using a pulse width modulation circuit or a reference voltage generator realized by combining a ladder resistor and a switch. May be used.

[0035]

As described above, according to the present invention, the following effects can be obtained. According to the first to fourth aspects of the present invention, the measurement is performed by maximizing the resolution of the A / D converter by adjusting the reference voltage of the A / D converter according to the state of the signal to be measured. It is possible to realize an electric signal measuring instrument that can perform the measurement.

This makes it possible to perform the measurement with a precision several times higher than that of the related art while using an A / D converter of the same degree as the related art. Therefore, a high-precision electric signal measuring instrument can be realized at low cost.

According to the fifth aspect of the present invention, a high-precision measurement with an increased SN ratio is performed by applying an auto-range circuit conventionally used in an electric signal measuring device to the electric signal measuring device of the present invention. Will be able to

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of an electric signal measuring instrument according to the present invention.

FIG. 2 is a flowchart illustrating the operation of the electric signal measuring device according to the present invention.

FIG. 3 is a diagram illustrating the operation of the electric signal measuring device according to the present invention.

FIG. 4 is a configuration diagram illustrating an example of a conventional electric signal measuring device.

FIG. 5 is a diagram illustrating a configuration of an A / D converter.

FIG. 6 is a diagram illustrating an example of a measurement signal waveform.

FIG. 7 is a diagram illustrating an input level with respect to a full scale of a conventional A / D converter.

FIG. 8 shows an input signal and A /
It is a figure showing the full scale of a D converter.

[Explanation of symbols]

 Vin Signal to be measured 1 Attenuator 2 Amplifier 3 A / D converter 4 Range switching signal generator 5 Insulation circuit 6 DSP 7 Operator 8 CPU 9 Display 10 D / A converter

Claims (5)

[Claims] An electric signal measuring instrument for digitally converting a signal under test and performing various measurements, comprising: an A / D converter having a reference voltage terminal for determining a full scale of an analog input; A signal preprocessing circuit for normalizing to an input level of an A / D converter; and monitoring the output of the A / D converter, and setting the reference value so that a peak value of the output falls within a predetermined range. An electric signal measuring device comprising: a reference voltage adjusting means for adjusting a signal of a voltage terminal; an arithmetic circuit for performing various arithmetic operations on an output of the A / D converter; and a control circuit for controlling the entire device. 2. The electric signal measuring instrument according to claim 1, wherein said preprocessing circuit includes a signal attenuator and an amplifier, and is configured to perform a plurality of range switching. 3. The A / D converter according to claim 2, wherein said reference voltage adjusting means includes a D / A converter for applying a reference voltage specified by said control circuit to a reference voltage terminal of said A / D converter. 2. The electric signal measuring device according to 1. 4. A reference voltage adjusting means for applying a reference voltage to a reference voltage terminal of the A / D converter such that a peak value of an output value of the A / D converter falls within a predetermined range. The electric signal measuring device according to claim 1, wherein the electric signal measuring device is configured to adjust a voltage. 5. The signal pre-processing circuit according to claim 1, wherein said signal pre-processing circuit includes an auto-range circuit for adjusting a magnitude of a signal to be sent to said A / D converter within a predetermined range. Electrical signal measuring instrument.