The use of computers in environmental simulation technology has become an international trend for representing advanced technologies of environmental testing equipment. Our company has already done this in this field, and is doing a lot of research and development work, has achieved some gratifying results, and also has many experiences, here to discuss with you.

1. Application in CAD Design

The application of computer-aided design has experienced a process from shallow to deep in our company. In the early days, we simply discarded the drawing board and replaced the pencil with a mouse. Of course, this also greatly improves our work efficiency. No matter in the design speed, accuracy, drawing quality and error rate, it has the advantages that traditional design can not match. Especially to make our drawings more standardized and standardized.

With the secondary development of CAD, our design work has really entered the essence of computer-aided design. We have our own gallery and customized a professional menu. The engineering database analysis system that is being established will all further improve work efficiency. Standardize design drawings and improve standardization. So as to ensure the quality of products and improve the consistency of quality. On the other hand, due to the shortened design cycle, our response to the market is more sensitive. With the deepening of the engineering database research work, we hope that in the future, we will not only provide users with a product of reliable quality and technical indicators that meet the requirements of the agreement. At the same time, with the help of our database analysis system, users can get the measurement points of this test chamber studio No-load and various different loads, temperature deviation curves under different volumes. Instead of merely proposing an index of temperature field uniformity, this will truly guarantee the success of product testing. The mathematical model established by a database system composed of a large number of previous projects that have successfully designed experimental data has made our product design calculations more accurate, reasonable and fast. This not only guarantees the product's technical indicators and reliability indicators, but also ensures the rationality of its power consumption, etc., and improves the product's cost performance. The ultimate beneficiary of cost reduction should be users.

The professional menu in CAD drawing is the secondary development result of our company's drawing design. For example, the design of our company's product packaging box no longer needs to draw the packaging box diagram, just click the packaging box in the menu and enter it in the dialog The product's depth, width, height, size and weight parameters are automatically drawn on the complete drawing of the entire package. The same is true for electrical backplanes. The heater bracket etc. have realized this parameterized automatic drawing method. This CAD secondary development guarantees the accuracy of each zero-year dimension in the drawings of various mechanical parts. Because what is calculated by the computer based on the mathematical model is unique. Avoiding errors caused by human carelessness, and also greatly improving our work efficiency. It frees designers from many repetitive tasks and engages in creative work.

Mechanical drawing from two-dimensional flat drawing to three-dimensional production is a turning point in our company's mechanical drawing design. The company spent a lot of money to purchase the three-dimensional production software Solidage, and organized many trainings, to improve our box structure design and low temperature piping system design.

We have started research on the subject of electrical design standardization and white dynamic design, and it is estimated that significant progress will be made in 2002.

2. Application in industrial control

Everyone is very familiar with the application of computers in the field of industrial control. The controller of the environmental test equipment has developed from the early simple moving coil instrument to the digital instrument and industrial control computer system composed of microprocessors. In particular, the industrial control computer system has completely changed the traditional control methods, regardless of the way of operation, the degree of automation, the accuracy of control, etc. have been greatly developed. Its great advantages are:

1. Friendly man-machine interface

For the operator, a good man-machine interface is very important. The complex menu structure of control instruments, especially temperature and humidity control instruments, numerous abbreviated keywords, and thick operation manuals make many operators, especially non-electrical professionals. The operator is intimidated, which makes the operation of the test box must be carefully trained and learned to gradually master the operation.

Our company has made many improvements on the man-machine interface. First, it is easy to operate. The software design is more typical, such as high and low temperature alternating humidity and heat test chamber. With the help of the powerful functions of WIN98, it provides rich Chinese Prompt and software fault-tolerant processing, with the help of 17 # large-screen display, the design will focus on frequently used operations and main display items on a display screen, while placing the temperature and humidity display in a conspicuous position, will The trend graph is enlarged as much as possible to highlight the theme. The temperature and humidity settings, the call of the curve, and the jump step are all directly operated at the corresponding display, without going to another menu. The operation process is further simplified. For all operation buttons and data setting boxes, corresponding fault-tolerant processing has been designed, and erroneous operations will be blocked and a prompt dialog box will be displayed.

For some special parameters, such as temperature, humidity correction, etc. are handled as a maintenance layer, because these parameters do not need to be modified by the operator, but are used for maintenance and debugging, so a password is set in the maintenance layer, without permission Can not be modified.

The system has also designed a self-checking alarm function. After the system is powered on, it monitors each alarm input point in real time. If there is an abnormality, an alarm screen will pop up to inform the operator that there is a certain type of fault somewhere, and the well will inform it of the solution.

In short, for the design of the human-machine interface, we strive to achieve the so-called "fool machine" operation. The purpose is to allow the operator to immediately master the operation without professional training and memory.

2. Increased automation

In the design of the software, we have summarized a set of control logic algorithms for various test chambers. For example: the opening of the refrigerator, the opening of the main heating, the opening of the auxiliary heating, etc. In the damp heat control instrument and the early industrial control computer software, the above-mentioned actuator action is realized by using a sequence and a toggle switch. For example, when setting the curve, set the timing curve at the same time to control the cooling. The auxiliary heating is turned on, and now we are based on the test environment temperature, the value of the set temperature point, the rate of temperature rise and other parameters to obtain the logic algorithm. Realize the automatic opening of these actuators. For general fixed value control, the operator only needs to set a temperature and humidity value and click the start button to complete all operations.

The system software also has functions such as scheduled start-up, scheduled shutdown, step skipping, time skipping, curve printing, report printing, average calculation, maximum and minimum calculation, etc., to meet different needs and improve the degree of automation.

3. Improved control accuracy

This is mainly for the characteristics of relative humidity control. At present, the temperature and humidity of the damp heat test chamber at home and abroad generally use the wet and dry bulb method, where the deviation of the PID calculation of relative humidity is relative humidity, namely;

VRH = RH-SRH

VRH: relative humidity deviation

SRH: relative humidity setting

RH: relative humidity sampling value

We know that the relative humidity obtained by the wet and dry bulb method is a function of temperature. At the temperature point near the ambient temperature, due to the small temperature difference between the temperature in the box and the ambient temperature, if the dehumidifier is not turned on, or The temperature of a constant temperature and humidity test chamber can easily fluctuate. For individual temperature tests, this temperature fluctuation system can control it within ± 0.5 ° C. However, in the wet heat test, during the temperature rise, the dry bulb temperature and the wet bulb temperature are not completely synchronized. The wet bulb temperature is slightly delayed. The instantaneous process produces the dry bulb temperature, and the wet bulb temperature difference increases, resulting in relative humidity. If it is reduced, the deviation of the PID calculation of relative humidity will increase, and the PID calculation output will increase. When the ambient temperature is close to the control temperature in the cabinet, due to the better thermal insulation and sealing performance of the test chamber, the temperature difference between the ambient temperature and the chamber is insufficient to overcome the overshoot temperature. During the test, the humidification output makes the temperature It can't fall down, but rises up, so that the temperature value slowly drifts away from the set value. This is the shortcoming of the current universal temperature and humidity instruments including the high-precision UP750 series instruments. The relative humidity PID calculation method developed by our company overcomes this shortcoming. We adopt the control of dry bulb temperature and wet bulb temperature instead of dry bulb temperature and relative humidity. No matter how the dry bulb temperature rises during the control process, the wet bulb temperature obtained by the relative humidity will not be lower than the set wet bulb temperature, so there will be no wrong humidification output, thus overcoming the temperature drift The phenomenon also makes the overall control performance better, the transition process is short, and the overshoot is small, which really solves the problem of difficult debugging of the damp and hot box.

4. Reliability growth

The reliability of the control system is a long-term research topic of our company. At present, we use PLC programmable logic controller as the lower computer to achieve data collection, operation control output, and PC industrial control computer as the upper computer display setting mode. Compared with the original module, A / D card, I / O card mode, the reliability has reached a new level.

The reliability of the programmable logic controller is well-known from the hardware. It is originally a controller designed for harsh industrial environments. We made full use of this in software design to use the PLC as an independent control. When the industrial PC is disturbed or powered off, the lower-level PLC is not affected. The industrial PC of the upper computer only serves as a receiving display and storing settings. It does not directly control external input and output. In addition, the system composed of industrial PC-type touch screen plus PIC will be more hardware, such as switches, buttons, indicator lights, intermediate relays and other software, the result is a reduction in hardware failure rate and increased reliability.

The PLC that we configure in the control system, the man-machine interface touch screen. Intermediate relays and other products are German Siemens products. This internationally renowned brand of products is difficult for ordinary small enterprises in terms of production scale, production process, detection methods, and versatility. Small enterprises can design and manufacture such Products, but the stability of its mass product quality cannot be compared with brand companies. The large scale and versatility also lower their product prices. Our design idea is to use the hardware products of internationally renowned brand companies to design special software suitable for environmental testing equipment, and the control system composed of them to achieve the reliability growth of products.

3. Application in standardized design

Most of the spare parts and electrical components of our company's test chambers use universal products, so we can easily shape the hardware of various test chambers. From the control system, we divide it into industrial control computer form, touch screen form and general control instrument form, so that we will shape each type of hardware and make a standard template for each form of electrical schematic diagram. In this way, in a sense, we have realized the automation and standardization of the electronic control design of products, especially non-standard products. Because for each specific non-standard design task, we no longer need to draw drawings, just select the corresponding drawings from the standard template and complete the design. This not only greatly speeds up work efficiency, but more importantly, it has been standardized from design to production process, thus ensuring the stability of product quality.

For example: an electrical designer received a design task requiring a high and low temperature test chamber controlled by an industrial computer. He only needs to select the relevant electrical schematic diagram, parts list, and fill in the number of each device in the product quota according to the requirements of the technical agreement. Yes, only the relationship between more and less, and the logical relationship among them has been softwareized, and only the software needs to be modified. In terms of hardware, the standardization factor is improved, and production processes, such as wiring and routing processes, are standardized. So as to ensure the stability of product quality.

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