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PROCESS CONTROL IN WET TANNERY The block diagram of the process can be interpreted as:

4

Get Input Signal from

Sensor

Signal Conditioning

Converting the signal to

digital form

Interfacing the signal with

8085 microprocesor

Programming the Microprocessor

Interfacing Circuit.

Load

2

INPUT FROM SENSOR

For temperature sensing LM35 Temperature sensor is used.

The output voltage of this 3 pin temperature sensor is directly proportional to the ambient temperature and is given by the formula:

Vout = K x TWhere, K = 10mV/oC (Sensor Constant), T= Ambient Temperature. For a temperature range of 0-100oC, the

output voltage varies from 0-1V in steps of 10mV.

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For pH sensing, PHE-45P pH sensor is used.

The PHE-45P is an electrode type sensor, which develops a voltage(potential) directly proportional to the concentration of H+ ions.

For a pH range of 0-14, the output voltage of the sensor varies from -0.41V to +0.41V.

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The output voltage from the pH sensor follows Nernst equation of equilibrium reduction potential.

Where,

E = reduction potential(voltage generated)

R = Universal gas constant( R=8.314 J/K-mol)

T = absolute temperature(T = 298K)

F = Faraday constant(F = 96485.33C/mol)

z = number of ions involved in the reaction.

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On substituting the values of constants, we get:

E = 0.4142 – 0.059pH.Hence, for a pH of 7, the potential would be 0,

for a pH of 0 (pure acidic), E = 0.41V

for a pH of 14(pure alkaline), E = -0.41V.

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SIGNAL CONDITIONING

The signal conditioning is done so as to interface the sensor’s output with the Analog to digital converter.

The main aim of this module is to convert the output of sensors i.e., 0-1V from temperature sensor and -0.41V to +0.41V from pH sensor to 0-5V which is the acceptable working range for an analog to digital converter.

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For temperature sensor, we use a simple non inverting amplifier circuit, given below:

Voltage Gain(A) = 5v/v.

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For pH sensor, we use an adder circuit coupled with an inverting amplifier:

The output voltage is 0-5V.

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CONVERTING TO DIGITAL FORM

ADC0809 is used for analog to digital conversion. The analog signal which we get from the sensors is amplified to 0-5V and is given to the ADC 0809.

The analog input from the temperature sensor is given at IN0 port of ADC.

The input port selection is done through the input selection lines(ADD A, ADDB, ADD C) which are connected to the programmable peripheral interface.

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The conversion starts when SOC(Start of Conversion) is given HIGH from the microprocessor through 8255.

When the analog input is converted to digital form, the EOC(End of Conversion) port goes HIGH, informing the microprocessor that the conversion is done.

The clock to the ADC is given from the microprocessor clock output.

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ADC 0809 PIN CONNECTION

.

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INTERFACING WITH MICROPROCESSOR

The digital output from the ADC is interfaced with the microprocessor through a programmable peripheral interface (PPI 8255).

PPI 8255 is a 40 pin IC which consists of three 8-bit I/O ports, a 8-bit Bi-directional data transfer port and a control logic buffer.

The block diagram of 8255 is as follows:

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.

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• Data Bus Buffer: It is an 8 bit data buffer used to interface 8255 with 8085. It is connected to D0-D7 bits of 8255.

• Read/write control logic : It consists of inputs RD¯,WR¯,A0,A1,CS¯ .

• RD¯,WR¯ are used for reading and writing on to 8255 and are connected to MEMR¯,MEMW¯ of 8085 respectively.

• A0,A1 are Port select signals used to select the particular port .

• CS ¯ is used to select the 8255 device .

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A1 A0 Selected port

0 0 Port - A

0 1 Port –B

1 0 Port – C

1 1 Control Register

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The 8255 PPI is initialized as below:

Port A - Assigned as Input

Port B - Assigned as output

Port CL - Assigned as Input

Port CU - Assigned as output

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The Port A takes input from the digital output pins of ADC.

The Port B gives signal to SOC, ALE and Input Select of ADC.

The Port CL takes input from EOC.

The Port CU gives the control signal.

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Control Word:

The control word for the PPI is – 1 0 0 1 0 0 0 1 i.e., 91H.

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MICROPROCESSOR 8085The features of INTEL 8085 are :

It is an 8 bit processor.

It is a single chip N-MOS device with 40 pins.

It has multiplexed address and data bus.(AD0-AD7).

It works on 5 Volt dc power supply.

The maximum clock frequency is 3 MHz while minimum frequency is 500kHz.

It provides 74 instructions with 5 different addressing modes.

It provides Acc ,one flag register ,6 general purpose registers and two special purpose registers(SP,PC).

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PIN LAYOUT.

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INTERNAL ARCHITECTURE:

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INSTRUCTION SET CLASSIFICATIONThe entire group of instructions can be classified

into five categories:

1. Data Transfer Operations. E.g. MOV, MVI, LDA,STA.

2. Arithmetic Operations. E.g. ADD, SUB, INR, DCR.

3. Logical Operations. E.g. ANA, ORA, XRA, CMP.

4. Branching Operations. E.g. JMP, CALL, RET, JZ.

5. Machine Control Operations. E.g. IN, OUT, PUSH, POP.

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.

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PROGRAMMING LOGIC:

• Configure 8255 I/O ports• 8085 sends SOC command to ADC• 8085 waits for EOC signal from ADC• 8085 reads 8-bit temperature value

from port A• 8085 compares the value with set

point value• 8085 generates the control signal to

control load.

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.

.

FLOW CHART .

START

Initialize 8255

CALL CONVERSION

IsTemp

> SETPP

T

Turn heater off

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PROGRAM:

 MVI A, 91HOUT CR

 BEGIN: CALL CONVERSATION

CPI 41HJC NEXTMVI A, 0EHOUT PCJMP BEGIN

 NEXT: MVI A, 0FH

OUT PCJMP BEGIN

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CONVERSION SUBROUTINE:CONVERSION:

MVI A,00HOUT PB ; Send address to select IN0MVI A,08H ;Latch address by giving ALE HighOUT PB

 BACK: MVI A,18H

OUT PB ; Make SOC HighMVI A,08HOUT PB ; Make SOC LowMVI A,00HOUT PB ; Make ALE Low

 LOOP: IN PC

ANI 01HJZ LOOP ; Wait for EOCIN PARET ; Return value and store Accumulator

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INTERFACING CIRCUIT

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The load, in this case a heater, is a device which operates under 230V ac.

The control signal from the microprocessor through the peripheral interface is of 5V magnitude.

A solid state relay device is used to interface the control signal with the load.