基于ds18b20的啤酒发酵温度测控系统毕业设计外文资料翻译

基于ds18b20的啤酒发酵温度测控系统毕业设计外文资料翻译内容摘要：

he bus by the DALLAS Corporation is only 100 meters, and 20 DS18B20s can be connected to it at same time, hence, the application is limited [2,4]. In order to solve this problem, we have designed transmission bus and its driver. The position of bus driver and bus converter is shown in Figure 3. Transmission bus includes two signal lines TXD and RXD. Bus driver adopts 74HC367type logical circuit to expand the driving ability of TXD port in AT89C51, thus it pletes to drive TXD line of transmission bus. The length of bus can be reached 500 meters. Multiple bus converters can be connected to a transmission bus to form “tree” or “star” work. Bus converter connects the transmission bus and the temperature sensor DS18B20 and pletes the signal conversion between them. DS18B20 return signal is transmitted to the terminal RXD of the bus through the driver. The driver in bus converter also uses 74HC367type logic circuit. The driver we mention here is different with the address switch of DALLAS corporation MicroLANs work [3]. The drivers on the bus are all connected to each other. When the skipping ROM mand is sent to DS18B20s, all DS18B20s existing on the bus can receive it. This feature allows us to start temperature conversion of all the DS18B20s existing on the same bus. The temperature detector can acquire the temperature of the different serial number detectingpoint by sending different address. This will greatly reduce the temperature detection cycle, thereby increasing the temperature detection speed. The Technology of Hardware Fault Detecting When one power line or data line of any DS18B20 in the system is short to the ground, it will cause the whole bus stop working. To avoid this problem, we have designed hardware fault detecting and processing circuits for the system. On the one hand, it limits the short circuit current under 10mA。 on the other hand disconnects the failure branch from the transmission bus. The position of hardware fault detecting and processing circuit see Figure 3. Fault detecting circuit tests the logic level of 1wire interface, when the logic level is high, its output signal is “1”and driver of converter is shutdown。 when the logic level is low, its output signal is “0” and driver of converter is open. If logic level is low and its duration is more than 10ms, according to these phenomena, we can judge hardware failure occurring, temporality, the output signal is “1”, and the driver of converter will be a permanent shutdown. Thus, only failure DS18B20 is disconnected from transmission bus, the other DS18B20s can work normally. Although a bus converter can be connected to 30 DS18B20s, when shortcircuit fault occurs in one of 5 DS18B20s, the other 29 DS18B20s will stop working. If each DS18B20 can work independently and it has no effect to others when there is shortcircuit fault occurring in one of them, it is necessary for each DS18B20 equipped with a bus converter. One transmission bus can connect more than 300 converters. The Design of Management Software Software of the temperature monitoring system is developed under VISUAL BASIC , it is responsible for the work of acquiring realtime temperature, sensor temperature pensating,displaying multipoint temperature value, showing temperature variation curve, the temperature value statements and the temperature variation curve printing. Module of acquiring realtime temperature is realized through Serial munication between the industrial Computer and temperature detector. Serial munication adopts RS232C standard, the baud rate of data transfer is the 9600 bit/s, the data format is 8 data bits, 1 parity bit, and 1 stop bit. Industrial puter collects temperatu。