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~: Industrial Temperature Controller :~
Abstract:- in most of the manufacturing industries like chemical, petrochemical, food processing, pharmaceutical etc temperature is one of the main parameter to be control. Because in these kind of industries some product need the required temperature to be maintained at highest priority otherwise the product will fail (in case of preparing any medicine in pharmaceutical company the temperature pays vital role. If it is not maintained then medicine may become poison.). So the temperature controller is most widely used in almost all the industries.
Its basically close loop control system. It may be simply ON-OFF type or continuous type system.
ON-OFF type: - It continuously senses temperature, displays it, compares it with set value. If its greater, then it switch off heating element and if its very less, then switch on heating element.
Continuous type:- It continuously senses temperature, displays it, compares it with set value. If its greater / less, then control the heat produce by heating element by changing its supplied current.
Here I have given an example of ON-OFF type close loop control system. Here the set value can be externally set by user for the temperature. Then the actual temperature is sensed by sensor, indicated on display with set value. If it exceeds set value then the heater is turned OFF. After then when temp falls bellow the specified limit again heater is turned ON. Also if there is failure in turning ON / OFF heater there is an alarm system. If the turning off heater failed and temperature goes on increasing then immediately the cooler/fan/AC is turned on and alarm sounds.
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The figure given below shows actual schematic diagram of the system.
The major components are micro controller 89C51, ADC 0848 and LCD. Other required components are temperature sensor LM35, relay driver chip ULN2003A and C/O relays.
Connections: - o/p of temperature sensor is connected with channel 1 i/p of ADC. Slider of 10K pot is connected as i/p to channel 2. The data bus (DB0-DB7) is connected with port P1. Control pins RD, WR, CS & INTR of ADC are connected with port P3 pins as shown. The data pins of LCD are connected with port P0 and control pins R/W, RS & EN are connected with port P2 pins as shown in figure. Pins P2.0 & P2.1 drives two relays through ULN chip one two switch on/off cooler and other to switch on/off heater.
Operation: -complete operation depends upon the software loaded in 89C51.
· Controller selects 2nd channel and receives data on P1 through ADC
· It displays this data on LCD as set value of temperature or reference temperature
· After 2 to 3 seconds controller selects 1st channel and get the data on P1 and display it on LCD as current temperature
· Then it compares current temperature with set or reference temperature
· If current temperature is lower, then heater is ON but if its higher then heater is turned off and cooler is turned on.
· now after every 2 / 3 sec of time controller takes the input from 1st channel, display it on LCD and compare it with set value and based on that either switch on cooler or heater Software and logic: - the software loaded in 89C51 has to handle ADC, LCD and also has to switch ON / OFF cooler or heater depending upon set and current temperature value. To handle the ADC
· first we have to apply active low signal to CS and WR signal and then latch the desired address of channel on MA0 to MA4 through P1
· Then we have to wait for INTR signal to be low. When it is low it means that conversion is over.
· When INTR becomes we have to apply CS and RD signal to read digital data from ADC on port P1
To handle the LCD
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The digital equivalent o/p that is received on P1 from ADC is in HEX format and to display it on LCD we have to convert it in ASCII
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So we shall separate lower nibble and upper nibble of received data byte. Convert them in to ASCII and then display them on LCD screen
Complete software is written in embedded C language and compiled using microvision Keil (IDE).
click here to view of c code | 
