【正文】 and is convenient to constitute bustype temperature detection system. The Composition of the System The position of temperature monitoring system of Beer fermentation is shown in Figure 1. Industrial Computer is responsible for the work of displaying temperature data, generating the curve of temperature change, and temperature chart printing and so on. Temperature detector can be connected to industrial puters through the RS232 interface. It controls the working condition of all the temperature sensors through transmission bus, and collects temperature data of 18 fermentation tanks in accordance with industrial puter mands. Temperature Detector is connected to 3 bus converter through the transmission bus, each bus converter can be connected to 6 fermentation tanks。 there are 3 temperature sensors (DS18B20) in each fermentation tank. The temperature monitoring system contains 54 temperature measurement points in 18 fermentation tanks. Transmission bus adopts the fourcore cables。Temperature detector provides power supply for bus converter and DS18B20 through transmission bus. There is a bus driver in temperature detector。 it can drive more than 500 meters transmission bus. If you need increase the number of temperature measurement points, more bus converters can be connected to transmission bus in order to achieve linking of more DS18B20s. The number of the DS18B20 can be connected up to more than 300 at most. 3 The Design of Temperature Detector The position of the temperature detector is shown in Figure 2, AT89C51 microcontroller is the core of the temperature detector to control the work of the various circuits. Control program is stored in the MCU39。s internal program memory. Data memory saves the temperature data of each detection point. 64bit code memory saves laser ROM code of each temperature sensor (DS18B20). MCU39。s serial signals are converted to RS232C standard through RS232 interface to realize the connection of industrial puter and the temperature detector. Bus driver extends the driving capability of MCU39。s I/O port to drive the transmission bus, in order to obtain further transmission distance. Watchdog and reset circuit can provide poweron reset for the microcontroller, they can also provide reset signal when program has been confused by accidentally interfering. Display is used to show the current number of fermentation tanks and temperature value of 3 sensors in fermentation tanks. The keyboard is used to control the temperature detector starting and stopping, but also enter the testing cycle and other control parameter. Temperature detector can work independently, and display the number of fermentation tank and temperature value of 3 detected points in this tank, the range of temperature shown is 176。C ~ 176。C. The number of tank shown can automatically change in cycle. Time shown can be set arbitrarily during 1~99 seconds. Temperature detector is also able to accept orders of industrial puter, it transmits the temperature value to the industrial puter, and then the industrial puter pletes data processing. The Design of Bus Driver and Bus Converter Theoretically, lots of DS18B20s can be connected to one bus in parallel. However, the operating time slot of DS18B20 is fixed, and the width of many control impulses is so narrow that it is only few microseconds. In fact, we can seldom meet the need of the operating time slot of DS18B20 because of the limit of driving ability and distributing parameters. Especially the increase of distributing capacitance of the overlong bus will make the distortion of waveform unavoidable, so the read/write 4 error occurs. The remended length of t