Development Of Multi-channel Temperature And Humidity Detection System

In view of our country current large-scale warehouse, large-scale granary status of monitoring and Icontrolling , This system carries on research and development and have designed a automatic monitring system of temperature and humidity of grain storage based on multi-level communication main line, including the design of communication control terminal as well as the lower position machine, Using more practical and the advanced signal-chip computer control system, Using sensitivity of the temperature sensor and the humidity sensor .The operator may send an order to the communication control terminal, extracting temperature and humidity data from lower position machine, realizing temperature and humidity examination of the lower position machine; Simultaneously may examine the historical examination data, carrying on a series of operation of grain sentiment analysis and grain storage management and so on .The Temperature-Humidity Measurement and Control System (THMCS) usually were considered as simple control technology. But as a result of that characteristics of most humidity sensors are unsteady and actual working life of the sensors were short. The most systems in application were not run in order unless the regulations were carried out strictly and multi-technology diathesis of system engineers must be up to the mustard. So in this paper, as the emphases we discuss and analyze the humidity sensitive characteristics and types for choice and correlative technology steps. On the basic of studying many kind of humidity sensors, I chose appropriate humidity sensors, which is one of the emphasis in this paper. In this design ,there is also an emphasis which is designing a analog switch and display part by the technology of CPLD.In this system, The upper position machine is PC machine and is connected with the switch through RS-232 interface , and the switch is connected with the lower position machine through RS-485 main line, realizing data communication between the control room and the scene. Each lower position is arranged in the various granaries, monitoring temperature and humidity signal. In order to realize 256-channel data acquisition , this system have designed a simulation switch using CPLD, Each time only a channel data is gathered and sent in the signal-chip computer; Moreover, the demonstration part of this design is also uniquely realized by CPLD . In normal condition, the upper position machine send out an examination signal to lower position machine every four hours (At the same time humiture situation can also be monitored at some granary in any time), The lower position machine realizes 128-channel observations and controls of temperature and humidity in the granary by using the PIC16F877 signal-chip computer.Control system of temperature and humidity is practical and reliable. And it have lower cost and high data transmission efficiency. It is not only applied in the monitoring and management of granary, but also extended to other areas of monitoring. Therefore it has a broad application prospect.