JP2009133698A - Zero point correction circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zero point correction circuit capable of correcting a zero point in a simple configuration while highly holding resolution of measurement. <P>SOLUTION: The zero point correction circuit of a measuring instrument includes an A/D convertor for A/D-converting an input signal and measures the input signal. The zero point correction circuit includes: an offset voltage setting means for outputting an offset voltage of the input signal in a multi-stage; and an adder for making a signal input to the A/D convertor in a prescribed range by offsetting the input signal based on the voltage output from the offset voltage setting means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a zero point correction circuit in a measuring apparatus, and more particularly to a zero point correction circuit capable of correcting a zero point with a simple configuration while maintaining a high measurement resolution.

In general, a measuring device requires zero point correction, and as a method for realizing this zero point correction, a method of taking a wide input range including zero point offset and processing it digitally (hereinafter referred to as “digital method”). And an analog circuit processing method (hereinafter referred to as “analog method”) in which an offset circuit is provided before the A / D converter. Prior art documents relating to such zero point correction include the following.

JP 09-287777 A

Japanese Patent Laid-Open No. 08-001138

Hereinafter, a conventional zero point correction circuit will be described with reference to FIG. FIG. 3 is an example of the zero point correction circuit of the waveform display device, and is an example of adjusting the offset voltage in an analog manner.

The ATT / AMP 10 includes an attenuator for adjusting the amplitude of an input signal and an amplifier. The ADC 11 is an A / D converter and digitally converts analog waveform data input from the ATT / AMP 10.

The waveform data processing unit 12 stores the waveform data input from the ADC 11 in a waveform memory 13 to be described later, or converts the waveform data into display data for display on the waveform display unit 14. The waveform memory 13 stores the waveform data input from the waveform data processing unit 12. The waveform display unit 14 is configured by an LCD (Liquid Crystal Display) or the like.

The DAC 15 outputs an offset voltage to be added to the input signal to the ATT / AMP 10. The control unit 16 is configured by a CPU, a memory, and the like, and gives a command related to an offset voltage to be output to the DAC 15. Various settings are made on the key input unit 17 by the user. The rotary encoder 18 adjusts the offset voltage by rotating left and right to adjust the zero point.

As described above, in the conventional analog zero point correction circuit, the DAC 15 adjusts the offset voltage by applying a voltage to the ATT / AMP 10.

However, in the circuit of FIG. 3, since the voltage is adjusted by the DAC 15, the circuit configuration becomes complicated if the peripheral circuit is included. Furthermore, since the resolution required for the DAC 15 needs to be higher than the measurement resolution, the price of the offset DAC 15 becomes expensive.

On the other hand, in the digital method, when the value of the A / D converter at the time of zero input is Vz and the value of the A / D converter at the time of measurement is Vm, the voltage Vo such as a measurement waveform output from the A / D converter. Is
Vo = Vm-Vz
However, if the offset voltage of the analog part is large, the measurable range must be larger than the rated value, so the measurement resolution must be reduced accordingly. In addition, the influence of noise increases.

  The present invention has been made in view of these problems, and provides a zero point correction circuit capable of correcting a zero point with a simple configuration while maintaining high measurement resolution.

In order to achieve such a problem, the invention described in claim 1
In a zero point correction circuit of a measuring apparatus that includes an A / D converter for A / D converting an input signal and measures the input signal,
Offset voltage setting means for outputting the offset voltage of the input signal in multiple stages;
An adder that offsets the input signal based on the voltage output from the offset voltage setting means to bring the signal input to the A / D converter within a predetermined range.

According to a second aspect of the present invention, in the zero point correction circuit according to the first aspect,
The offset voltage setting means includes an ATT that attenuates a reference voltage and a SW that attenuates the reference voltage attenuated by the ATT in multiple stages.

  The present invention has the following effects. Since the reference voltage is input to the adder via the ATT and the measurement range is set within the rated range, the zero point can be corrected with a simple configuration while keeping the measurement resolution high. As a result, even if the analog offset is large, it is not necessary to take a wider measurement range than the digital zero point correction circuit, and the zero point can be corrected without reducing the resolution.

Hereinafter, a configuration example of the zero point correction circuit of the present invention will be described. FIG. 1 shows a configuration example of a zero point correction circuit of the present invention. The ATT 20 is an attenuator and attenuates the reference voltage. The SW 21 is connected to the output of the ATT 20 and is a switch that switches and outputs a reference voltage attenuated to an adder 22 described later in multiple stages. Moreover, the offset voltage setting means 25 is comprised by ATT20 and SW21.

A waveform to be measured is input to the adder 22 and a value attenuated via the ATT 20 is input. The ADC 23 is an A / D converter. The control unit 24 commands the SW 21 of the offset voltage setting unit 25 which offset voltage is to be output.

Although the waveform display unit, waveform memory, and the like shown in the example of FIG. 3 are necessary for operating the waveform measuring apparatus, they are irrelevant to the essential part of the present invention. Description is omitted.

Next, the operation of FIG. 1 will be described with reference to FIG. FIG. 2 is a diagram for explaining the operation of the present invention. The vertical axis in FIG. 2 is the voltage axis, and the horizontal axis means that the zero point correction procedure proceeds from left to right. Therefore, the zero point correction procedure needs to follow FIG. 2 in order from the left side to the right side.

First, the analog zero point is measured. Then, Vz1 (analog offset amount 30) is obtained, and the pre-correction input range 31 is determined based on this Vz1. Incidentally, the pre-correction input range 31 is out of the rated range 33. Therefore, if the input range (that is, the actual measurement range) is set to this position, measurement cannot be performed with high accuracy.

Therefore, when the zero point becomes larger than a certain value, the control unit 24 switches the offset voltage setting means 25 to shift the analog input. Here, the shift amount 34 is Vs. In this state, the analog zero point is measured again. The zero point Vz2 after correction is
Vz2 = Vz1-Vs
It is calculated by the following formula.

Since the offset can be corrected through the above procedure, the input of the measured waveform or the like is measured in this state. Here, it is assumed that an analog input value Vm is added to the adder 22. When the output voltage of the adder 22 is Vo, Vo is
Vo = Vm−Vz2
This value is obtained as a true measurement value.

Specifically, the zero point is obtained as follows.
Measurable range 32 ± 1V
Rated range 33 ± 0.8V
in the case of,
If the analog offset is 0.2 V or more, the rated range is out of the measurable range.

Therefore, the zero point is set using the offset voltage setting means 25 and the adder 22 having the following characteristics capable of realizing the present invention. First, the switching point of the offset voltage setting means 25 is
+0, ± 0.1V, ± 0.2V
If the measured value at the zero point is 0 to 0.1 V, the set value of the offset voltage setting means 25 is “0”.

Similarly, the relationship between the measured value of the zero point and the offset voltage setting means 25 is as follows.
Measured value of zero point 0.1-0.2 ATT -0.1
Measured value of zero point 0.2 to 0.3 ATT -0.2
Measured value of zero point -0.1-0 ATT 0
Measured value of zero point -0.1 -0.2 ATT 0.1
Measured value of zero point -0.2 to -0.3 ATT 0.2

  Hereinafter, the case where the analog offset is 0.05 V, 0.11 V, and 0.25 V will be taken as an example to explain that the measurement range (corrected input range) falls within the rated range 33.

First, when the analog offset amount 30 is 0.05 V, 0 <vz1 <0.1
Therefore, the ATT20 output is “0”, that is, Vs = 0. Therefore, the zero point after correction is
Vz2 = Vz1 = 0.05
It becomes.

Next, when the analog offset amount 30 is 0.11 V, 0.1 <Vz1 <0.2
Therefore, the ATT output is “−0.1”, that is, Vs = −0.1. Therefore, the zero point after correction is
Vz2 = Vz1-0.1 = 0.01
It becomes.

Finally, taking the case where the analog offset amount 30 is 0.25 V as an example,
0.2 <Vz1 <0.3
Therefore, the ATT output is “−0.2”, that is, Vs = −0.2V. Therefore, the zero point after correction is
Vz2 = Vz1-0.2 = 0.05
Thus, the measurement range falls within the rated range.

  Note that when only the digital method is used, in order to make the measurement range fall within the rated range, for example, the rated range must be widened by ± 0.7 V, resulting in a decrease in resolution. In addition, the influence of noise is increased.

In the present invention, the offset voltage setting means 25 comprising a combination of ATT 20 and SW 21 is used for zero point correction, but a DA converter may be used. In general, the DA converter is more expensive than the ATT, but even in that case, the correction operation is only once as described above, and the rough correction in analog is sufficient. There is no need to use a converter, and the cost can be reduced compared to the prior art.

In this way, by inputting the value attenuated via the offset voltage setting means 25 to the adder 22, the measurement range is set within the rated range, so that the zero point can be corrected with a simple configuration while maintaining the measurement resolution. Can do. As a result, even if the analog offset is large, it is not necessary to take a wider measurement range than the digital zero point correction circuit, and the zero point can be corrected without reducing the resolution.

It is a block diagram of the zero point correction circuit by this invention. It is explanatory drawing of operation | movement of this invention. It is a block diagram of the analog type zero point correction circuit by a prior art.

Explanation of symbols

20 ATT
21 SW
22 Adder 23 ADC
24 Control unit 25 Offset voltage setting means

Claims (2)

In a zero point correction circuit of a measuring apparatus that includes an A / D converter for A / D converting an input signal and measures the input signal,
Offset voltage setting means for outputting the offset voltage of the input signal in multiple stages;
An adder that offsets the input signal based on the voltage output from the offset voltage setting means to bring the signal input to the A / D converter into a predetermined range. Point correction circuit.   2. The zero point correction circuit according to claim 1, wherein the offset voltage setting means comprises an attenuator that attenuates a reference voltage and a switch that attenuates the reference voltage attenuated by the attenuator in multiple stages.

Images