JP3311464B2 - Signal measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal measuring apparatus having improved measurement accuracy, and more particularly to a signal measuring apparatus capable of measuring a signal under measurement with high accuracy even when calibration cannot be performed for a long time.

[0002]

2. Description of the Related Art A signal measuring device such as an oscilloscope is
An error occurs in the measurement accuracy of the input signal (signal to be measured) due to aging or temperature change. Therefore, in order to maintain the measurement accuracy, it is necessary to repeat the calibration of the measurement characteristics of the measurement device such as the gain, the operating gain (linearity of the gain), and the frequency characteristics as necessary. In particular, digitized signal measuring devices in recent years are equipped with a microprocessor (microminiature processing unit), and when the operator arbitrarily performs calibration, or the device itself performs self-calibration every time a predetermined time elapses or temperature changes. Those that have the function to perform are becoming common.

FIG. 1 is a block diagram of an example of a signal measuring device having a self-calibration function. The measured signal (input signal) to be measured is input terminal (BNC connector) by a probe etc.
10 is supplied. The vertical input circuit 12 is a circuit for increasing the input impedance, and receives a signal to be measured from the input terminal 10. Digital processing circuits include memories such as RAM,
It is composed of an analog / digital (A / D) converter, a microprocessor, and a bus connecting these components. The A / D converter converts the signal under measurement from analog to digital to generate measurement data. This measurement data is stored in the memory. The microprocessor performs these controls and arithmetic processing of the measurement data. The vertical output circuit 16 converts the digital data from the digital processing circuit 14 from digital to analog, and supplies an analog signal indicating a vertical change of the signal to the display device 18. The trigger circuit 20 generates a trigger signal when the signal under measurement exceeds a predetermined level that can be arbitrarily set. Thus, it is detected that a desired signal to be measured has been input. The sweep generation circuit 24 generates a sweep signal in synchronization with the trigger signal. The horizontal amplification circuit 26
The sweep signal is amplified and supplied to the display device 18. As a result, the signal under measurement is displayed on the display device 18.

The calibration circuit 30 has a high-precision DC signal source. Based on the high-precision DC signal generated by this signal source, a DC signal serving as a reference for calibration or a rectangular wave signal of a predetermined frequency (for example, 1 MHz) is generated. A plurality of calibration signals (reference signals) are generated. These calibration signals are input to the input terminal (B
(NC connector) 10, a vertical input circuit 12, a sweep generation circuit 24, and the like. By measuring the values of these calibration signals whose values are known, errors in measurement characteristics such as gain (vertical axis), operating gain, sweep speed (horizontal axis), and frequency characteristics can be found, and each circuit can be calibrated. it can. For example, when a DC voltage of 1 V is input to the input terminal 10 by switching the switch 11, the gain is calibrated so as to be measured as 1V.
The temperature sensor 34 is provided for detecting a temperature change, and there is also a signal measuring device that automatically enters a self-calibration mode when a temperature change of a predetermined value or more occurs.

[0005]

A signal measuring device which automatically performs a self-calibration operation every time a predetermined time elapses or a temperature change, etc., maintains the measurement accuracy within a certain range without the operator's particular consciousness. It is very useful in that However, in the case of such a measuring device, the measurement accuracy is high immediately after the calibration is performed, but the measurement accuracy decreases as the next calibration is performed. When the calibration mode is entered, measurement cannot be performed during that period. Therefore, for example, when measuring a signal of an event that occurs only accidentally once every several hours, it is necessary to continue to wait for the signal to be measured without entering the calibration mode, and the measurement accuracy decreases during this time. Ideally, the measuring device should be calibrated just before receiving the signal under measurement. However, when measuring a signal of an event that occurs accidentally once every several hours (the occurrence time is unpredictable), it is impossible to perform calibration immediately before the generation of the signal to be measured.

In addition, during a period of, for example, about 30 minutes after the power is turned on, measurement accuracy cannot be guaranteed unless calibration is frequently performed due to a rise in temperature of the measuring apparatus. In other words, the measurement has to be interrupted frequently to enter the calibration mode frequently, or the measurement has to be performed without considering accuracy. Otherwise, it was necessary to wait for the start of the measurement until the temperature of the measuring device was stabilized.

Accordingly, an object of the present invention is to provide a signal measuring apparatus capable of measuring a signal under measurement with almost the same accuracy as that measured immediately after calibration, even when calibration cannot be performed for a long time or when frequent calibration is required. It is to be. Another object of the present invention is to provide a signal measuring device capable of measuring a signal under measurement with higher accuracy using a conventional self-calibration function.

[0008]

The signal measuring apparatus of the present invention is most suitable for measuring an accidentally occurring event, for example, about once every several hours. The input detecting means 20 detects the input of the signal under measurement. The analog-to-digital conversion means converts the signal under measurement from analog to digital to generate measurement data. A storage unit such as a RAM stores the measurement data. The calibration signal generator 30 generates a calibration signal. This signal measuring device operates as follows. The storage means stores the measurement data and then measures the signal under measurement.
Is completed , the calibration signal output by the calibration signal generating means 30 is measured to determine a measurement characteristic error of the signal measuring device, and the measurement data of the measured data of the signal to be measured which is already stored in the storage means using the measurement characteristic error. Calibrate the error. The calibration of the error of the measurement data is performed by a calculation circuit such as a microprocessor, for example. Subsequently, the calibration signal may be measured to perform self-calibration of the circuit of the signal measuring device as in the related art.

[0009]

According to the present invention, the measured data is calibrated after storing the measured data of the signal under measurement. In other words, immediately after the measurement of the signal under measurement, the measurement characteristic error is obtained immediately before the time of measurement, and the measurement data is calibrated in consideration of the measurement characteristic error, so that highly accurate measurement data can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be widely applied to a signal measuring apparatus as shown in FIG. Therefore, the following description is made with reference to FIG. FIG. 2 is a flowchart of one embodiment of the present invention. This is performed under the control of a microprocessor included in the digital circuit 14. The software executed by the microprocessor may be stored in a memory such as a ROM in the digital circuit 14.

The signal measuring device according to the present invention comprises a trigger circuit 20
Detects the input of the signal to be measured (step 42), the analog-to-digital (A / D) converter in the digital processing circuit converts the signal to be measured from analog to digital,
And the like (step 44). After the storage of the signal under measurement is completed, the calibration circuit (calibration signal generating means) 30 transmits the calibration signal under the control of the microprocessor to the input terminal (B
(NC connector) 10, the vertical input circuit 12, the sweep generation circuit 24, and the like (step 46). Each circuit measures this calibration signal (step 48), so that the measurement characteristics such as the frequency characteristic, the gain, and the operating gain (linearity of the gain) are measured in a normal state (calibrated state) and a present state (calibrated state). ), That is, an error in the measurement characteristics can be obtained (step 50). If this measurement characteristic error is known, the error of the measurement data of the signal under measurement stored in the memory can be known, and this is calculated by a microprocessor (or a dedicated arithmetic circuit) to calibrate the measurement data (step 52). That is, it is a feature of the signal measuring apparatus of the present invention that calibration (post-calibration) is performed immediately after the measurement data of the signal under measurement is measured. This post-calibration is performed after the measurement time, but after measuring the measurement characteristic error of the signal measurement device immediately before the measurement time, and then calibrating the measurement data. In comparison, higher measurement accuracy is obtained.

The end of the signal under measurement may be detected, for example, by detecting when the signal level has dropped below a predetermined value. As is well known, the end may be detected by providing a plurality of levels or setting a point in time after a predetermined time has elapsed from the start of signal storage.
A memory such as a RAM is becoming inexpensive, and it is easy to secure a sufficient storage capacity for storing measurement data of a signal under measurement.

When calibrating the measurement data of the signal under measurement stored in the memory, if the measurement characteristic error of the signal measuring device becomes too large to be regarded as a first-order approximation (linear), the data of the signal under measurement is calibrated. There is a possibility that complicated calculations of second or higher order need to be performed. However, recent signal measurement devices such as oscilloscopes require that the calibration of data of the signal under measurement requires a complex second-order or higher calculation.
It is rare that the accuracy is greatly reduced. Therefore, according to the post-calibration according to the present invention, it is possible to increase the measurement accuracy of the conventional signal measurement device and collect data of the signal under measurement with extremely high accuracy without requiring much complicated calculation. Becomes possible. However, if the period until the next signal under measurement is generated is long (for example, several hours), and thus cannot enter the calibration mode for a long period of time,
After the calibration of the measurement data of the signal under measurement, the calibration of the measuring device itself (step 53) may be performed. FIG.
Is a flowchart in this case.

In order to calibrate the measurement data of the signal under test stored in the memory with higher accuracy, a calibration signal having substantially the same frequency and amplitude as the signal under test is selectively generated from the data of the signal under test stored. Then, the measurement characteristic error of the signal measuring device may be obtained. For example, both the frequency and the amplitude may be generated with a certain width around the value of the signal under measurement, and the linearity error of the measurement characteristic may be obtained. Furthermore, if the data of the signal under measurement is analyzed by performing a fast Fourier transform (FFT) and the signal under measurement includes a plurality of harmonics, a calibration signal of a corresponding frequency may be generated to obtain a measurement characteristic error. good. As a result, the measurement characteristic error can be accurately obtained according to the signal under measurement, and thus the data of the signal under measurement can be calibrated with very high accuracy.

In the embodiment shown in FIG. 1, an example of a signal measuring device using a vector display type display device, for example, an oscilloscope is shown, but a signal measuring device using a raster scan type display device may of course be used. . As a signal measuring apparatus to which the present invention is applied, a spectrum analyzer or the like can be considered in addition to an oscilloscope.

[0016]

According to the signal measuring apparatus of the present invention, measurement data can be obtained with high accuracy even if calibration cannot be performed for a certain period. Therefore, there is no need to wait until the temperature of the measuring device becomes stable after turning on the power,
Even a signal to be measured that occurs only once in a long period can be measured with high accuracy. In addition, in implementing the present invention, if various signal measuring devices already having a self-calibration function are used, the present invention can be easily implemented with only a slight improvement, and can be widely applied.

[Brief description of the drawings]

FIG. 1 is a block diagram of an example of a signal measuring device suitable for applying the present invention.

FIG. 2 is a flowchart showing a flow of one embodiment of the operation of the signal measuring device of the present invention.

FIG. 3 is a flowchart showing a flow of another embodiment of the operation of the signal measuring device of the present invention.

[Explanation of symbols]

 Reference Signs List 10 input terminal 11 changeover switch 12 vertical input circuit 14 digital processing circuit 16 vertical output circuit 18 display device 20 input detection circuit (trigger circuit) 22 trigger level setting means 24 sweep generation circuit 26 horizontal amplification circuit 30 calibration signal generation circuit (calibration) Circuit) 34 Temperature sensor

Claims (2)

(57) [Claims] 1. A signal measuring apparatus for measuring a signal under test, an input detecting means for detecting an input of the signal under test, and an analog-to-digital converter for converting the signal under test into analog-to-digital to generate measurement data. measuring means, storage means for storing the measurement data, comprising a calibration signal generating means for generating a calibration signal and terminates the measurement of subsequently the signal to be measured to store the measurement data the calibration signal A measurement characteristic error of the signal measurement device, and using the measurement characteristic error to calibrate an error of the measurement data already stored in the storage unit. 2. A signal measuring device for measuring a signal under test, an input detecting means for detecting an input of the signal under test, and an analog-to-digital conversion for converting the signal under test into analog-to-digital to generate measurement data. measuring means, storage means for storing the measurement data, comprising a calibration signal generating means for generating a calibration signal and terminates the measurement of subsequently the signal to be measured to store the measurement data the calibration signal Then, the measurement characteristic error of the signal measuring device is obtained, the error of the measurement data already stored in the storage means is calibrated using the measurement characteristic error, and the calibration signal is measured subsequently, and the signal is measured. A signal measuring device for performing self-calibration of a circuit of the measuring device.