[Abstract] This paper introduces the basic method of developing ITE temperature transmitter controlware via VB and two linearization processing schemes for signal conversion, solving the key and difficult problem in designing controlware for each instrument. [Keywords] Controlware design, instrument controlware, ITE temperature transmitter, interface design, linearization processing, linear input Developing a multifunctional simulation laboratory requires solving two major problems : the development of instrument components and the construction of the experimental system. The development of instrument components is the foundation for developing a multifunctional simulation laboratory, just as the purchase of experimental instruments and equipment is necessary for establishing a laboratory. Therefore, we design commonly used instruments and equipment in the form of instrument controls to provide the necessary material basis for the construction of the experimental system. The reason we make each meter into a meter control is that meter controls, as visual objects, have excellent encapsulation characteristics. Encapsulating a well-designed meter control makes it just like using a real device that you have purchased. Users do not need to know the specific internal implementation of its functions to easily use its external functions. In addition, well-designed meter controls can be reused in different meter systems, which greatly improves the efficiency of program development. 1. Working Principle of ITE Temperature Transmitter The ITE temperature transmitter is a major product of the I-series transmitter unit. It can be used with various standard thermocouples or resistance temperature detectors (RTDs) to continuously convert the measured temperature or temperature difference signal into a unified 1-5V, 1x2 or 4-20mA, DC signal output. This signal can be used as a standard input signal for display, recording, regulating instruments, and industrial control machines. Its circuit mainly consists of two parts: a linearization input circuit and an amplification output circuit. The entire unit operates based on the negative feedback balance principle. The block diagram of its information transmission and conversion process is shown in Figure 1. As shown in Figure 1, the measured temperature t is converted into a corresponding thermoelectric potential E[sub]t[/sub] by the thermocouple and then input to the linearization input circuit of the temperature transmitter. This potential is then combined with the feedback voltage V[sub]f[/sub] output from the linearization circuit and the voltage v[sub]t[/sub] output from the zero-point adjustment and cold junction compensation circuit. Finally, the signal is sent to the voltage and power amplifier for amplification and conversion into a current signal. The current signal is then converted into a 1-5V, IX2 or 4-20mA, IX2 signal output via an isolation output circuit. Simultaneously, the J signal is converted into a corresponding feedback voltage Vf through the feedback resistor of the feedback circuit, and then input to the linearization circuit for processing, resulting in an output voltage Vt. This voltage is then fed back to the inverting input of the voltage amplifier, achieving negative feedback for the entire device. When the entire circuit is in a balanced state, its output current I_o (or voltage V_o) has a linear relationship with the measured temperature t. The linearization circuit of the temperature transmitter is mainly designed based on the non-linearity between the thermoelectric potential output by the primary element thermocouple and the measured temperature. This is a special problem in the design of thermocouple temperature transmitter controls and also a difficult problem in the design. Its principle is shown in Figure 2. In addition, the ITE temperature transmitter also has an automatic compensation function for the cold junction temperature of the thermocouple. Implementing this function is slightly more complicated for actual instruments, mainly because it requires a temperature sensing element and a compensation circuit. However, for analog instruments, there is no actual temperature environment, and the so-called cold junction is provided by the user. Therefore, the cold junction compensation problem becomes an algebraic compensation problem, so it is relatively simple to simulate and will not become the main problem in the development of this instrument. 2 Design of Instrument Controls This design is carried out under the Windows 98 operating system, using 3DMAX 2.5 for instrument interface design, and Chinese Visual Studio 6.0 for control design and system programming. 2.1 Instrument Interface Design The design of the instrument interface (i.e., the design of the appearance) strives to be consistent with the actual instrument, so that users can use it as if they were using an actual instrument. Previously, instruments were designed using the Paint tool in the Windows operating environment, resulting in a simple appearance and a lack of three-dimensionality. To increase realism, we used 3D Studio MAX to create realistic 3D models, then added materials, textures, lighting, etc., achieving a lifelike 3D effect from any angle. 2.2 Instrument Control Design Control design mainly involves designing the implementation code of the control's "member functions," that is, the implementation code of the control's "properties," "methods," and "events." The following is a brief introduction to the ActiveX control development process using the ITE temperature transmitter control as an example. First, after entering the VB application, select the "ActiveX Controls" project and set the "Project Name" to "Temperature Transmitter." Set the "Name" property of the "User Control" to "ITE," and set its "ToolboxBitmap" property to the "Instrument Image Name" drawn in 3D MAX. This completes the design of an empty instrument control, i.e., an instrument shell without any functionality. To enable instruments to perform specific functions, it is necessary to add corresponding "properties," "methods," and "events." To add "properties," "methods," and "events" to a control, select the "Add Procedure" item under the Tools menu. This opens the Add Procedure box. In the Name field, give the property name (e.g., Input). In "Type," select the "Property" button. In "Range," select the "Public" button, and then click OK. This creates two procedures for the "Input" property: Let (assignment) and Get (retrieval) procedures. For ITE temperature transmitters, their main function is signal conversion. Based on their usage characteristics, they should have input and output signal attributes, instrument measurement range (instrument's scale) attributes, and output model type (voltage or current output) attributes. They can also have a "Reset" method and a "Bad Value Input" event. Below is the main attribute procedure code for a temperature transmitter: Because a temperature transmitter is a signal conversion device, its output cannot be manually changed; it can only change with the input. Therefore, the output attribute does not need an assignment (Let) attribute procedure. The other attribute processes are similar and will not be listed here. The "methods" and "events" of controls are relatively simpler. A "method" is a "public procedure" or "public function procedure." An "event" is activated in the program code when the conditions for triggering the event are met, using the keyword "RaiseEvent" + event name. Users can program the event when using the control. For instrument control design, simply designing the control's "properties," "methods," and "events" is far from sufficient. To provide users with a realistic and user-friendly instrument, dynamic effects during use must be considered. For example, for instruments with display output, the pointer should move accordingly when the input changes. Additionally, the instrument's accuracy and the automatic scaling function of the instrument control are also important considerations. 3. Linearization Processing of ITE Temperature Transmitters The mathematical model of the ITE thermocouple temperature transmitter is as follows: Since the transmitter input can only be a millivolt signal, the linearization circuit of the thermocouple temperature transmitter can only be simulated by indexing the temperature value corresponding to the millivolt value. Therefore, the software implementation of the ITE thermocouple temperature transmitter is more complex. Currently, I have two solutions to address the linearization input problem. Solution 1: Use Access database in Office to create a thermoelectric potential-temperature correspondence calibration table. Use the output millivolt signal of the thermocouple to index the temperature value, then substitute the returned temperature value into the output equation to obtain the output value. When implementing this in the programming language, the thermocouple output signal is the transmitter's input value. Utilize VB's database connection function to load the calibration table and index the temperature value. For example, at calibration B, if the input thermocouple millivolt signal is 13.820mV, we can index row 138, column 20 of the calibration table to find the temperature value of 1820℃, substitute it back into the output equation, and obtain the output result. Solution 2: Define a multidimensional array in the program and assign a value to each element. The array dimension corresponds to the conversion of the millivolt input value, and the element values ​​are the temperature values. For example, array B(i, ) corresponds to the B scale table. When the input signal is 13.820, array B(13.820) - 1820℃ will automatically be substituted into the output equation and used as input for calculation. Both of the above methods are relatively cumbersome, and the table needs to be loaded into memory or the values ​​assigned during the initialization phase. However, in terms of resource consumption, the use of multidimensional arrays is relatively less, and values ​​can be dynamically assigned in the program, which will reduce resource consumption. Therefore, the author adopted the second approach. 4 Summary Developing a complete multifunctional simulation laboratory requires a lot of manpower, material resources, and financial resources. The above short article mainly introduces the development ideas of instrument control and the handling of special problems (linearization) in the development of ITE temperature transmitters. It is hoped that it can provide some inspiration to friends who are interested in this topic and serve as a starting point for further discussion. References 1 Cary Cornell, Dave Jezak. Activex VB5 0 Control Creation Edition. Beijing: Tsinghua University Press, 1998: Complete Book 2 Li Hai. Visual Basic Advancement: Activex Controls. Beijing University of Aeronautics and Astronautics Press. 2000: Book 3. Guo Qiaoju. Development of General Simulation Software for Visualized Process Control Systems. Computer Applications Research, 2000. 1 (Supplement) 69-70. Development and Linearization Processing of ITE Temperature Transmitter Control: PDF