Dissertation for obtaining a master's degree in electrical engineering in electronics
Abstract
The many advantages of on-site calibration compared to calibration in the calibration center have led to the formation of well-equipped mobile calibration teams in all companies that work in the field of calibration. Therefore, in recent years, the design of standards and equipment suitable for mobile work has been given attention. Designing standards that are optimal in terms of weight and facilities while having the necessary accuracy is the subject of many recent researches and designs in the field of calibration. Among the manufactured devices, multicalibrators have the best structure in terms of weight and dimensions. But one of the most important disadvantages of this type of calibrators is the complex design and the fundamental difference in their appearance compared to old calibrators. The large number of available quantities and familiarity with all of them is a complicated and sometimes impossible task for an expert. The presence of more specialists in a mission team increases the cost. Considering that most quantities must be converted to current, resistance and voltage for measurement. Therefore, in this system, we have produced voltage, resistance, frequency, etc. quantities and with the help of a software, we have made it possible to produce other quantities related to voltage and resistance, such as temperature, humidity, pressure, etc. We have provided the appropriate appearance, simplicity of operation and learning of the device. Focusing more on software instead of hardware in the design leads to the elimination of electromechanical parts as a result of a significant reduction in the weight of the device and the possibility of adding new features without changing the hardware from the use of software. The future can easily provide the possibility of remote calibration by developing the software part.
Keywords:
Calibration, Standard, Calibrator
Foreword
Humans have used various tools to achieve more prosperity and whenever the existing tools did not meet their needs, they started to produce new tools and improve their quality. Improving the quality requires the ability to accurately measure the specific parameters of each tool and device in order to guarantee its quality within an acceptable range. To ensure the acceptable accuracy of the measurements made, the need for standard references with high accuracy is felt so that the accuracy of the device can be calculated by comparing the measured quantities with these references. Various methods have been used to make standard measuring devices in the world, each of which is useful and practical in its own way. Considering the increasing mechanization and the increasing speed of life, the need for a system with low volume and weight and the possibility of faster access is felt. The purpose of this article is to present methods for building a standard mobile calibration laboratory in such a way that, in addition to high accuracy, it will be easier to use by reducing volume, weight and price. Hardware with each other, standard methods of communication between electronic chips have been used.
Since this system has its own problems and shortcomings, all professors, enthusiasts and students are requested to help me improve the next versions of this system with their criticisms and suggestions regarding possible software and hardware defects.
Calibration [2]
Many definitions for Calibration provided. In the national standard of Iran, in the "Basic and general terms of metrology" section, calibration is defined as follows:
Comparison of a precision instrument with a laboratory standard reference in standard conditions, in order to ensure its accuracy and health, and to determine the amount of error of this device compared to that standard and its adjustment compared to the standard.
Another definition that can be provided is that:
Calibration is the comparison of two measuring systems or devices. (one with known uncertainty and the other with unknown uncertainty) in order to calculate the uncertainty of a device whose uncertainty is unknown.
Another definition in ISO10012 introduces calibration as: a set of operations that are established under certain conditions and determine the relationship between the values ??indicated by the measuring device and the corresponding values ??of that quantity by the reference standard.
Another definition in ISO10012 introduces calibration as: a set of operations that are established under certain conditions and determine the relationship between the values ??indicated by the measuring device and the corresponding values ??of that quantity by the reference standard. be: grading the device, setting the electrical circuits on the device such as setting digital indicators, estimating the uncertainty and stability of the device.
After these steps, the measuring device is used according to its lifespan. Recalibration is required to ensure the correct functioning of the devices and to control the quality of their components. Therefore, with recalibration, it is possible to identify the factors and components of the device that have lost their quality.
The reason for calibration
Primary calibration shows the customer how to measure the efficiency claimed by the manufacturer. The parameters measured by the device are referenced to traceable measurement standards that cannot be guaranteed otherwise.
Recalibration is necessary to control and maintain the measurement processes performed with the measuring device. Usually, the uncertainty of the device increases over time and with repeated uses. Identifying the gradual growth of uncertainty and its increase is not easily possible by the user. What is essential in measurement is traceability. Establishing traceability, which is made possible by calibration, is essential in the control of the measurement system and international trade.
Traceability
The ability to relate the value of a standard or the result of a measurement with national and international references, through a continuous chain of comparisons that all have a certain uncertainty, determined or determined nationally or internationally. production, final tests and calibration of products and equipment before delivery. Also, traceable calibration makes it possible to ensure that the measurement uncertainty in one part of the process affects other parts of the process. The validity of the measurements depends on the correct estimation of the phenomena under study and the obtained uncertainties. The calibration of the instruments used in the research determines the uncertainty and controls the growth of the uncertainty and helps the researcher to be confident in the results of his research; that these results are caused by real changes in the phenomenon; Not due to the inaccuracy in estimating measurement uncertainties.
Calibration time
Determining the calibration time is one of the most important and significant decisions, which, of course, leads to a waste of time and money. Measurement uncertainties cause incorrect decisions to be made, which are caused by deceptive measurement results.
The goal is to perform recalibration at optimal intervals; So that there is a balance between the cost of calibration and the costs of non-calibration. Currently, to determine the recalibration intervals, more attention is paid to the expected accuracy percentage of the measuring devices; This percentage can be obtained from its specifications. The magnitude of this percentage indicates the low chance of incorrect measurement by the measuring device. Some users choose this percentage to be 95% or more in order to be more sure of the quality control of the measurement; which also depends on the general quality policy and policy in the relevant company. Therefore, the selection of this percentage is contractual and the easiest acceptable choice is 85-90%. The process of determining the calibration time is a mathematical and statistical problem and requires correct and sufficient data during calibration.
Calibration place
Calibration is done in reference laboratories. Calibration can also be done at the location where the measuring device is used. This action has the following advantages:
Tensions caused by moving the device are minimized.
Calibration is simpler and cheaper because it is done only at the points desired by users.
Users can be sure of the protection of their devices.
Calibration is done in the shortest time and there is no interruption in the device's performance.
Among the disadvantages of this practice, the following can be mentioned:
1- Changes in environmental conditions may affect the reference devices.