JPH0648198B2 - Automatic zero correction method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a detector for comparative measurement, for example, a detector using a differential transformer, which relates to a circuit for automatically correcting the zero point for measurement. .

These detectors determine the zero point by the reference zero master work, and measure by the difference from this, but the zero point is deviated due to mechanical deviation.

Therefore, the zero point is corrected before the measurement. The present invention is a technique relating to this zero point correction.

<Prior Art> In FIG. 2, the digital display value is now full scale ± 1.
When the digital measurement is performed in the range of 00, it is assumed that the zero point is the point A which is shifted to the right from the 0 position. At that time, in the prior art, the digital signal value at the point A was stored, and the digital signal value at the point A was subtracted from the display value digitally displayed by the measurement signal to create the measured value.

However, in this case, when the measurement sensitivity is doubled (the amplification factor of the operational amplifier is doubled), the numerical value at the point A is also doubled, and the measurement range up to the maximum reading of the measurement range is narrowed (the dynamic range is narrowed). ).

For example, if the measurement sensitivity is increased 10 times by increasing the amplification factor of the operational amplifier 3, the minimum resolution at the point A of 100 μm becomes 0.1 μm, and a full scale display device of 100.0 μm can be obtained.

At that time, 36 μm at point A becomes 36.0 μm, and the full scale of the display becomes ± 10.0 μm, and the measurement point cannot be displayed, or if the display is left as it is ± 100 μm, the zero point correction of 0.1 μm range is possible. It will not be possible.

Therefore, a resolution of 0.1 μm can be obtained from the beginning 4
If a digit A / D converter is prepared, it is possible to obtain an accuracy resolution equivalent to ± 100 even when the amplification factor increases 10 times (in the case of 1 μm reading, 0.1 μm level (Ignore the display), but with high resolution in the A / D converter.
There is a drawback that a multi-bit type is required, which causes a problem in cost.

Also, in order to achieve high resolution, such a complicated circuit is required, and as a result, reliability against noise decreases,
There is a drawback that analog factors such as temperature drift increase and it is difficult to handle.

<Means for Solving the Problems> Here, in FIG. 2, when the zero point shift A is 36 μm, a rectified signal from the detector and a setting unit from the CPU for calculating the rectified signal are set in units of 10 digits. If cut, N ×
(Setting unit) is the analog amount passed through the D / A converter by 3 × 10 and the zero point is shifted to the left, and the setting unit is 10 μm.
The following digital value of 6 μm appears from the output of the operational amplifier.

This 6 μm is stored in the CPU, and the value of the output of the display by the signal of the detector circuit is digitally calculated to obtain the zero point.

Here, if the setting unit is 5 μm, N = 7 and n = 1.

In this way, the number of zeros set is less than or equal to the set number of units, so the degree to which the measurement range is narrowed can be made extremely small. Further, there is no need to change the A / D converter to a high precision multi-bit converter.

<Examples> Examples of the present invention will be described below with reference to the drawings.

In FIG. 1, the signal output from the detector 1 is the rectifier circuit 2
Is converted into a DC analog signal.

This analog signal is converted into a digital signal by the A / D converter and stored in the CPU 6.

Then, it enters the D / A converter 7 through the I / O port 5 and generates a constant analog voltage for a set unit (10 or 5 in the above description), and the output of the detector circuit causes the operational amplifier 3 to output the analog voltage. Perform analog calculation.

At this time, the CPU repeatedly sends the data to the D / A converter 7 repeatedly so that the output of the operational amplifier 3 (the input signal to the A / D converter 4) becomes the value closest to zero, that is, the set unit or less, and the set unit or less. A /
It is passed through a D converter and digitally stored in the CPU as an automatic zero point setting value.

With this, the preparation for the automatic zero adjustment is completed, and the actual measurement is started.

With respect to the output from the detector circuit in the measurement, a voltage corresponding to N × (setting unit) is input from the CPU to the D / A converter 7 in the operational amplifier 3 and is operated to calculate n.
The + measurement value signal enters the A / D converter 4, and the stored n is subtracted from this in the CPU, and the true value is sent to the display 8.

<Effect> Conventionally, if the first set of detectors is greatly out of alignment, the measurement range is narrowed accordingly, so it was necessary to use nerves in the set of detectors, but in the present invention, the set of detectors Since it has nothing to do with the deviation and the measurement range of amplification factor expansion, the operation became easier.

Moreover, since the full width of the A / D converter is effectively used,
An A / D converter with a small resolution can be used, a circuit can be assembled at a low cost, and its practicality is significantly improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, and FIG. 2 is an explanatory diagram for zero point setting. 1: Detector, 2: Rectifier circuit 3: Arithmetic circuit, 4: A / D converter 5: I / O port, 6: CPU 7: D / A converter

Claims (1)

[Claims] 1. A rectification circuit for rectifying the signal by inserting a reference zero master work into a detector that emits an analog signal.
The signal and the set unit value signal set by the CPU are D
/ The signal converted to DC by the A converter is calculated by the operational amplifier, and the value that minimizes the signal output is stored in the CPU, and the measured value of the CPU is stored in the display output by the measurement signal of the detector circuit when measuring the workpiece. Automatic zero correction method to calculate and output.