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What is the relationship between product measurement knowledge and methods and digital quality?

We believe that: RoHS Approved Manufacturer of metallic valve

If you can measure a thing and express it numerically, you have a deep understanding of it; but if you do not know how to measure it and cannot express it numerically, then your knowledge may be Barren and unsatisfactory.
We understand quality through ‘rules’ and ‘moments’. Only when there is measurement, can there be data, when there is data, there is calculation, when there is calculation, there is analysis, and when there is analysis, there is optimization, and when there is optimization, there is guarantee.
Measurement is perceptual quality, digitization is to solve “know why” on the basis of “knowing it”, and be good at using mathematics to solve problems, in order to avoid “it seems right, but it is wrong”.

If you agree with the logic of the above point of view, then let’s learn the basics of the digital quality business layer together:

Measurement accuracy

The measurement accuracy is one of the most important parameters of the instrument. The accuracy of most instruments is basically one percent, one thousandth, and some can reach one ten thousandth. The higher the accuracy, the smaller the measurement error, then How is the error defined? RoHS Approved Manufacturer of metallic valve

Terminology of measurement error

True value: The true value of the measurand itself is an ideal concept, which is generally difficult to know.

Specified truth value: The state establishes various physical standards that remain unchanged as much as possible, and in the form of a decree, specifies the value embodied by it as the specified value of the unit of measurement, also called the agreed truth value.

Actual value: The state constitutes a value transmission network through a series of physical measurement standards at all levels, and compares the measurement units reflected in the national benchmark level by level, and transmits it to the daily work instruments or measuring tools. In each level of comparison, the value reflected in the standard of the previous level is regarded as the correct value.

Nominal value: The value marked on the measuring instrument.
Due to insufficient manufacturing and measurement accuracy and the influence of environmental factors, the nominal value is not necessarily equal to its true value or actual value, so the error range or accuracy level should also be marked. RoHS Approved Manufacturer of metallic valve
For the nominal value of 100HZ, the working error is ≤±3%±1HZ
The actual value is 100±100×3%±1HZ

Indication: The measured value indicated by the measuring instrument. There may be differences between the indicated value and the reading of the measuring instrument.

Classification of measurement errors

According to its nature and characteristics, measurement errors can be divided into three categories: systematic errors, accidental errors (random errors) and negligence errors.

system error

Under certain measurement conditions, the measurement value contains errors that are fixed or change according to certain rules, which are called systematic errors.

Systematic errors are usually caused by errors in measuring instruments, measuring instruments and the instrument itself. In addition, the error caused by the imperfection of the measurement method and the tester’s testing habits is also called systematic error.

The size of the systematic error can measure the degree of deviation of the test data from the true value, that is, the accuracy of the measurement. The smaller the systematic error, the more accurate the measurement results. RoHS Approved Manufacturer of metallic valve

Elimination or reduction of systematic errors

Eliminating the factors that cause systematic errors is the most basic method to reduce systematic errors:

–Choose instruments and equipment with a high level of accuracy to eliminate the basic errors of the instrument;
–Make the instrument and equipment work under the specified conditions to eliminate the additional error of the instrument and equipment;
–Choose a reasonable measurement method and design correct measurement steps to eliminate method errors and theoretical errors;
–Improve the measurement quality of the measurement personnel and improve the measurement conditions to eliminate personnel errors.

Eliminate the use of correction methods

During the data processing of the measurements, the measurement readings or results are automatically or manually added to the correction values to eliminate or attenuate systematic errors from the measurement readings or results. RoHS Approved Manufacturer of metallic valve

Eliminate the use of special measurement methods

Substitution method: first connect the measured Ax to the measuring device, adjust the measuring device to be in a certain state, then replace Ax with the same standard quantity AN as the measured one, adjust the standard quantity AN, and restore the measuring device to its original state, so Ax=AN.

Difference method: measure the difference a between the measured Ax and the standard quantity AN, that is, a=Ax-AN, and use Ax=AN-a to find the measured value.

Positive and negative error compensation method: Under different measurement conditions, measure the measurand twice, make the error of one measurement result positive and the error of the other measurement result negative, and take the average value of the two measurement results as the measurement result Methods.

Symmetrical observation method: In the measurement process, the measurement steps are reasonably designed to obtain symmetrical data, and the corresponding data processing procedures are used to obtain measurement results independent of the influence quantity.

chance error

It is caused by the sum of small changes of many complex factors, and its change law is unknown, but it has all the characteristics of random variables and obeys statistical laws under certain conditions. Therefore, after many measurements, the sum can be described by statistical laws. . For example: slight changes in electromagnetic fields, fluctuations in temperature, air disturbances, micro-quakes in the earth, and irregular small changes in the senses of the measuring personnel. These changes are uncontrollable and irregular, which makes it impossible for the measurement results to be exactly the same. If they are the same, it only means that the sensitivity of the instrument is insufficient. RoHS Approved Manufacturer of metallic valve

Although random errors cannot be eliminated by humans, random errors are normally distributed. That is, the probability of occurrence of small measurement error is high, while the probability of occurrence of relatively large error is small, and the probability of occurrence of positive and negative errors of equal size is also equal.

The random error distribution law of the normal distribution:

Symmetry Positive and negative errors of equal absolute value occur in equal numbers
Unimodality Errors with small absolute values occur more often than errors with large absolute values
Boundedness Under certain measurement conditions, the absolute value of random errors will not exceed a certain limit
Compensation As the number of measurements increases, the arithmetic mean of random errors tends to zero

omission error

Under certain conditions, the measurement result deviates significantly from the corresponding error of its actual value. The measurement value containing the negligence error belongs to the suspicious value or abnormal value, which cannot participate in the data processing of the measurement value and should be eliminated.

There are two main reasons for it:
One is caused by the experimenter himself;
The second is due to measurement conditions. RoHS Approved Manufacturer of metallic valve

Qualitative judgment of negligence error: analyze the measurement conditions, measurement equipment, and measurement steps to check whether there are errors or factors that cause negligence errors, and the measurement data can also be compared with other personnel using other methods or the results measured by different instruments. Check to detect oversights.

Quantitative judgment negligence error: Based on the negligence criteria established by statistical principles and relevant professional knowledge, outliers or bad values are eliminated.

Three error comparisons

The difference between these three errors can be taken as an example of shooting. The bullets in Figure 3-a are evenly located on the bullseye, which indicates that there is no systematic error, but the dispersion of the distribution indicates that the accidental error is relatively large. The impact point in Figure 3-b is biased towards the bulls-eye, indicating that the system error is large. The bullet impact points in Figure 3-c are close to the bull’s-eye, indicating that there are only random errors and no systematic errors.
picture
Figure 2. Three kinds of errors are illustrated by target shooting

Representation of measurement error and calibration of instrument accuracy
Absolute error

The difference between the measured value X of the measurand and its true value A is called the absolute error of X. The absolute error is represented by △x, that is, △x=X-A.

Because from a measurement point of view, the truth value is an ideal concept that cannot be really obtained. Therefore A is usually replaced by the exact measurement x0. RoHS Approved Manufacturer of metallic valve

Relative error

Absolute error can only express how closely a measurement is approximated. However, two measurements of different magnitudes have different degrees of accuracy when their absolute errors are the same. For example, when measuring the distance from Beijing to Guangzhou, the error is 1 meter, which is not a big error, but if the error is 1 meter when measuring the distance from Tiananmen Square to the Great Hall of the People, then the error is relatively large. In order to measure the accuracy of measurement values more accustomedly, the concept of relative error is introduced.

The ratio of the absolute error to the true value of the measured value is called the relative error of the measured value.

Instrument error and accuracy

Absolute error and relative error reflect the error of a certain measurement value from the representation of error and the result of measurement, but they cannot be used to evaluate the accuracy of measuring instruments.

When the meter works under the specified normal conditions, the ratio of the absolute error picture of its indication value to the range picture is called the introduction error of the meter, which is represented by a picture, that is, a picture, because the reference error takes the range picture as the comparison object, so it is also called is the reference error. The maximum reference error of the measuring instrument in the entire range is called the allowable error of the instrument, that is, the allowable error is the picture. The errors indicated in the technical specifications of the instruments refer to the allowable errors.

For the pointer type instrument, set the absolute value of the allowable error as the picture, the picture in the formula—the accuracy level of the instrument, which indicates the size of the absolute value of the allowable error of the instrument, which is what we usually call the accuracy. RoHS Approved Manufacturer of metallic valve

Elimination of systematic errors

Eliminate errors introduced by measuring instruments and meters

In the measurement process, instruments and meters with different accuracy levels should be selected according to the requirements of the measurement accuracy;

Eliminate errors caused by measurement methods or theoretical analysis;

Errors caused by some factors that are not fully considered before the measurement, but are involved in the measurement, are often caused by insufficient theoretical analysis or the use of approximate formulas. These situations should be avoided.

Eliminate errors caused by surveyors

Errors caused by physiological characteristics such as the experimenter’s reaction speed and inherent habits are human errors. For example, when recording a signal, the observer has a tendency to lead or lag, and the tendency varies from person to person, which will inevitably lead to errors, so these factors must be considered when measuring.

Eliminate the influence of errors through data analysis and observation

To sum up, completely accurate measurements do not exist in actual testing. Whether it is the systematic error of the instrument, the accidental error, or the negligence error, it cannot be completely avoided. However, we can use scientific methods to reduce the error as much as possible and make the measurement data closer to the true value. The most perfect and effective method and tool is to conduct long-term analysis and observation through the data to avoid the influence of errors. RoHS Approved Manufacturer of metallic valve