Designing and building a multi-channel temperature measurement system with the capabilities of storage, processing, display and sending through the network.

Dissertation for Master of Electrical Engineering degree in Electronics

Abstract

Precise temperature measurement and control in industrial and research systems is of particular importance, and the correct operation of some industrial and laboratory tools is possible only in a specific location with a small number of channels (maximum 8 channels). Therefore, we decided to build a 64-channel temperature measurement system with the goals of measuring with an accuracy of up to 0.25 degrees Celsius, dispersion in a space of up to 900 meters (depending on the type of cable), measuring 64 channels in a maximum time of 1 second, accurate display of temperature on the computer and the possibility of uploading data.

This system uses a powerful ARM7 microcontroller to perform the necessary calculations and communicate between two powerful and famous TCP/IP and RS485 networks. It uses an AVR microcontroller to measure the temperature and pack it. Each AVR microcontroller on the side boards measures the temperature of 4 thermocouples and packages them in a special format and sends them to a computer program at the same time. Also, a powerful computer software has been written for this system that performs display, storage, loading and various processing tasks. To evaluate the accuracy and performance, we tested the system for a long period of time (2 to 3 days) and the desired results were obtained. This system has a good accuracy and temperature range, so it can be used in industrial buildings, greenhouses, poultry breeding centers and research works.

This system is currently designed to measure the temperature of K-type thermocouple, but with a slight change in the side boards, it is possible to read the value of any type of sensor (convert its data to digital) and send them to the computer program in a special package intended for data. It can also be converted into a control system with minor changes in peripheral boards and computer program.

Keywords

Temperature Datalogger, Displaying Temperature, Processing on Temperature Signal, Ethernet, Digital Filter

Foreword

Measuring and recording tools for physical parameters, in the laboratory industry and General uses have many uses. Today, the advancement of technology and the use of electronic components, in addition to the ease of use of tools, have brought with them very high accuracy and greater economic efficiency. To measure this physical quantity, there are many different methods and we have chosen the thermocouple measurement method, which is widely used in the industry. This project consists of two parts, hardware and software, in the hardware part, it has been tried to use common chips in the market, and standard methods of communication between electronic chips have been used to connect different parts of the hardware with each other. To analyze, display, record information, load and also control the performance of the hardware part, a complex software has been designed in the LabVIEW environment.

Since this system undoubtedly has its faults and deficiencies, all of you professors, enthusiasts and students are requested to help me improve the next versions of this system with your criticisms and suggestions regarding possible software and hardware defects and deficiencies.

Concept Temperature

From a physical point of view, heat is a quantity of the inherent energy of an object, which is caused by the random movement of its molecules and atoms. For example, just as increasing the speed of a tennis ball increases its energy, the internal energy of an object also increases with increasing temperature. Temperature is a parameter that expresses the amount of energy of an object with other parameters such as mass and the like.

The primary standard of temperature is Kelvin. At zero degrees Kelvin, all molecules of a substance are at complete rest. In this state, they no longer have any heat energy of their own, and this means that in this state, we will not have a more negative temperature because the energy level of the molecules will not go lower than this..

1-2- History of temperature measurement[2]

In 1592, there was no correct definition of temperature. An Italian scientist named Galileo did a series of experiments and was able to build a thermometer consisting of a bubble, a glass tube connected to it and a container filled with water in which the tube was placed (Figure 1-1). In such a way that the inside of the glass bubble is full of air and as a result of the heating of the air trapped inside this bubble, a pressure was applied to the water column inside the tube and it moved the water downward. Measure the temperature. But there was a big problem in the work of this type of thermometer, and that is that the rise or fall of the liquid level did not happen only because of the heat or cold of the air. Rather, other factors such as changes in atmospheric pressure also contributed to this work, which revealed the inaccuracy of Galileo's thermometer.

In 1631, Ray proposed changes to Galileo's thermometer. His proposal was Galileo's inverted bottle, in which only cooling and heating were recorded due to the contraction and expansion of water.

In 1635, Duke Ferdinand of Tuscany, who was interested in science, made a thermometer in which he used alcohol (which freezes at a temperature much lower than the temperature of water) and closed the end of the tube so tightly that the alcohol could not evaporate. Finally, in 1640, scientists at the Lynchian Academy in Italy made a prototype of a new thermometer that used mercury and removed at least some of the air from the top of the closed tube. It is interesting to note that it took about half a century for the thermometer to fully evolve.

Following the discovery of the thermometer by Gabriel Daniel Fahrenheit, the Dutch scientist in the 17th century made a type of gas and alcohol thermometer that can measure air temperature with greater accuracy. In 1714, he designed a mercury thermometer and calibrated it with a high accuracy factor in a special way. Fahrenheit published the results of his research in 1724. He also defined a special scale for heat, which later and even to this day has been named after him. He was inspired by the cold winter of 1709 and used a mixture of ice, solid ammonium chloride, and water to determine the zero degree. By choosing this zero, he hoped that he would not have more negative temperatures.

In 1742, the Swedish Celsius announced that he had discovered a simpler and more practical scale instead of the Fahrenheit thermal scale. He used two specific points that could be produced anywhere in the world as a reference for his work. One was the melting point of ice at zero degrees Celsius and the other was the boiling point of water at 100 degrees Celsius. He divided the distance between them into 100 equal parts, and this made it possible for any thermometer to be easily adjusted and calibrated at these two points (0 and 100 degrees Celsius).

Fahrenheit: The origin of this scale is not exactly clear, but it has been reported that zero Fahrenheit was obtained by placing the thermometer bubble in a mixture of ice and chloroammonium, and the highest point of this scale is the temperature at which mercury begins to boil; Between these two temperatures, it is divided into 600 degrees, where the freezing point of water is 32 degrees and the boiling point of water is 212 degrees Fahrenheit. Kelvin: In the SI system, absolute temperature is measured in degrees Kelvin. In fact, absolute zero on the Kelvin scale is -273 degrees Celsius, considered by its inventor Lord Kelvin, this temperature is the lowest possible temperature and at this temperature the kinetic energy of molecules reaches zero. The following relationships can be used to convert temperature units: (°C + 273) = °K.                                                                                                 (1-1)

(°C × 1.8) + 32 = °F.