Master of 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. Future generations can easily provide the possibility of remote calibration by developing the software part. rtl;">
Calibration[2]
Several definitions of calibration are provided. In the national standard of Iran, in the "basic and general terms of metrology" section, calibration is defined as follows:
Comparison of a precise instrument with a laboratory standard reference in standard conditions, in order to ensure its accuracy and health, and to determine the error rate of this device compared to that standard and to adjust it compared to the standard.
Another definition that can be provided is this. which:
Calibration is the comparison of two measurement systems or devices (one with known uncertainty and the other with unknown uncertainty) in order to calculate the uncertainty of the device whose uncertainty is unknown.
Another definition given in ISO10012 introduces calibration as: a set of operations that are established under specific conditions and the relationship between The values ??indicated by the measuring device and the corresponding values ??of that quantity are determined by the reference standard.
Usually, the initial calibration of the test and measuring device (TME) is done in the stage of its construction and production, which can include these steps: calibration of 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. Re-calibration 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 the device measures the efficiency claimed by the manufacturer. The parameters measured by the device are referenced to traceable measurement standards, otherwise there can be no confidence in them.
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. The establishment of traceability, which is made possible by calibration, is essential in the control of the measurement system and international trade. Traceability is the ability to relate the value of a standard or the result of a measurement to national and international references, through a continuous chain of comparisons, all of which have a certain uncertainty determined or specified nationally or internationally.
One ??of the essentials of any research is the design of production activities, 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 misleading measurement results. 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 accurate and sufficient data during calibration. Calibration can also be done at the location where the measuring device is used. This practice 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 performance of the device.
The disadvantages of this practice can be mentioned as follows:
1- Changes in the environmental conditions on the reference devices may have an effect.
2- The dimensions of the reference devices may cause problems.
3- On-site calibration involves additional costs.
How to calibrate
The quality and cost of calibration depends on the calibration method and the number of examined points. The cost of calibration is one of the important and determining factors in doing it. Costs vary in different calibration methods; Therefore, it is necessary to provide more explanations about the types of calibration methods. Calibration systems can be divided into the following four groups.