Smart Sterilizer

1.    INTRODUCTION

Sterilization is a process making the equipments fee from all micro organisms which are not detectable with standard culturing method There are so many procedures for the serialization purpose. Some of the important procedures are steam sterilization, liquid sterilization, dry heat sterilization etc. In the case of steam sterilization the steam under high pressure is used for the sterilization purpose.

Under ordinary circumstances (at standard pressure), liquid water cannot be heated above 100 °C in an open vessel except for special situations. Further heating results in boiling, but does not raise the temperature of the liquid water. However, when water is heated in a sealed vessel such as an autoclave, it is possible to heat liquid water to a much higher temperature. As the container is heated the pressure rises due to the constant volume of the container (see the ideal gas law). The boiling point of the water is raised because the amount of energy needed to form steam against the higher pressure is increased

The SMART STERIZER is an advanced version of an ordinary autoclave. The working procedure of this table top sterilizer is similar as that of autoclave. But here some additional controls are present. That is, automatic time control temperature control etc.

2.    BASIC PRINCIPLE

The basic principle of steam sterilization process is that the steam is much heavier than air. So steam enters the chamber, it fills the upper areas as it is tess dense than air. This compresses the air to the bottom, forcing it out through a drain. Often a temperature sensing device is placed in the drain. Only when air evacuation is complete should discharge stop. Flow is usually controlled through the use of a steam trap or a solenoid valve, but bleed holes are sometimes used, often in conjuction with a solenoid valve. As the steam and air mix it is also possible to force out the mixture from locations in the chamber other than the bottom.

Steam sterilization is generally carried out at 121°C (250°F) for 15 minutes or at 134°C for 3-4 minutes. Temperatures can be reduced to 115°C, and even as low as 105°C, depending upon the bi bio burden integrity, heat resistance, and characteristics of the material being sterilized. Low-temperature steam processes (65°-80°C) have been used (e.g., steam-formaldehyde); however, other combinations could also be used.

Steam (water vapor) is a ubiquitous compound. Steam delivers high heat condensation, and it is an activating agent. Before a dormant spore can begin germination and outgrowth, it must be activated. However, at higher-temperatures, steam becomes spermicidal. Sterilization, by definition, destroys or eliminates resistant microbes, including bacterial spores such as anthrax.

More-resistant microorganisms (e.g., prions) cannot be eliminated using most standard methods. Extended and high-steam sterilization, however, can at least reduce the effectiveness of these organisms. Using the classical definition of sterilization, it is an absolute criterion. A method has to be capable of destroying or eliminating all forms of life. In practice, however, Sterilization is best defined as a process that is capable  of delivering a certain probability that an exposed or treated product or material is free from viable microorganisms, including resistant microbial spores.

3.    BLOCK DIAGRAM

PRESSURE VALVE

CHAMBER              COIL

AMPFIER

SAFTY TEMPARATURE LIMIT

HEATER ELEMENT CONTROL

ADC

ALARM VISUAL                                AUDIO

SYSETM PROCESSOR                                 CONTROLLER

USER INTERFACE KEYS

LM35IC

FIG 3.1

4.    BLOCK DIAGRAM DESCRIPTION

The important blocks present in the case of a table top sterilizer are as explained below:-

CONTROL UNIT

The entire control of this table top sterilizer relies on a microcontroller 1C (89C51), which is an 8-bit microcontroller available in 40-pin 1C package. The major sub unites of this control unit are - Temperature control:-here we can select appropriate temperature cycle for different objects to be sterilized. In this case there are two temperature cycles -hot cycle (130 c) and cold cycle (110 c). Time control:- here we can select proper time periods -sterilization time and dry time. When the temperature in the chamber reaches to the selected temperature cycle (hot or cold), the sterilization time will start to count down, when it reaches to zero dry time will start. When the dry time is over the sterilization process is completed.

TEMPERATURE SENSING UNIT

For the accurate measurement and monitoring of the temperature inside the sterilization chamber, a precise sensing unit is required .For this purpose a LM35 heat sensor 1C is used which is placed inside the chamber. LM 35 is a temperature transducer which converts the temperature into corresponding voltage level.

AMPLIFIER AND ADC SECTION

The output voltage from the thermocouple corresponding to the temperature is in the micro voltage range. Hence there is amplifier section Is needed for further processing of the signal .The section includes a non inverting amplifier. In order to feed this analog signal to microcontroller it should be converted into digital form .Hence there is an ADC section is needed.

KEYBOARD AND DISPLAY SECTION

This section includes four keys for select the variables and an LCD display is used for the visualization of these variables.

POWER SUPPLY SECTION

This section will supply appropriate power to various sections of the circuit Here we use three pin regulator Ics for this purpose.

CHAMBER AND HEATING COIL

This section consists of completely closed, pressure with stand able stainless steel chamber with gasket and a 10QOw heating coil.

5.    CIRCUIT DIAGRAM

FIG 5.1

6.    CIRCUIT DESCRIPTION

The circuit diagrams of the smart sterilizer consist of the following sections:

POWER SUPPLY SECTION

It consist of a step down transformer (12v), center tapped rectifier, filter circuits and a regulator 1C The main role of this section is to provide appropriate power to the various sections. A capacitor filter is used to filter out the ac components. The regulator 1C used is 7805(5v).

AMPLIFIER AND ADC SECTION

The output voltage from the thermocouple corresponding to the temperature is in the micro voltage range. Hence there is amplifier section is needed for further processing of the signal The section includes a non -inverting amplifier. An op-amp CA 3130 is used as the non inverting amplifier. This will provide the maximum gain.

The signal from the amplifier is analog on nature and it is then converted into digital form by using an ADC the ADC 0804 is used for this purpose.  ADC08O4

The ADC0804 is CMOS 8-bit successive approximation A/D converters that use a differential potentiometric ladder similar to the 256R products. These converters are designed to allow operation with the NSC800 and INSSOSO A derivative control bus with TRI-STATE output latches directly driving the data bus. These A/Ds appear like memory locations or I/O ports to the microprocessor and no interfacing logic is needed. Differential analog voltage inputs allow increasing the common-mode rejection and offsetting the analog zero input voltage value. In addition, the voltage reference input can be adjust  to allow encoding any smaller analog voltage span to the full 8 bits of resolution.

7.    CONTROL SECTION

The heart of the control section is a 89C51 microcontroller 1C which controls and co ordinates the entire operation of the device. A 6 MHZ crystal is used to drive the microcontroller .Which is connected in between the 18^th and 19^th terminal .An RC network is connected to 9^th terminal(RST) of the microcontroller for the proper working of the microcontroller. For switches and 3 control signals of the LCD is connected to the port 0 of the controller. The output of ADC is connected to the port 1 of the controller. A 100k resistor package is connected to the port 0 because of it has no pull up resistor .port 0 is an address/data port. Port 2 is directly connected to the data pins of the LCD The data from the controller is given to the LCD through this 8 lines of port 2. port 3 (2,3,4) is used for giving the control signals to the relay and buzzer driver sections.

RELAY AND BUZZER DRIVER SECTION

A single contact 6 A relay is used here for provide constant supply to the heater element. Two NPN transistors (BC 547, TIP 122) are used for drive the relay. The buzzer driver section includes A 10 k resistor and a PNP transistor (BC 557). This will drive the buzzer.

LM35 PRECISION CENTIGRADE TEMPERATURE SENSORS

TheLM35 series are precision integrated-linear temperature sensors calibrated in * Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. TheLM35 does not require any external calibration or trimming to provide typical accuracies of ±WC at room temperature and ±34°C over a full -55 to +150°C temperature range. Low cost is assured by trimming and calibration at the wafer level.The LM35'slow output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy.

8.    WORKING

The power supply section will generate the 12V and 5V then supply to the various sections. Here we use 1 regulator Ic, when the output voltage coming from the secondary winding of the transformer is rectified and filtered, then given to the first pin of the regulator Ic. The Ic regulates the voltage into appropriate level.

The voltage output of the LM 35 IC is amplified by using a non inverting amplifier (CA 3130). This will provide the maximum gain (A= 1+Rf/R1). An RC network is connected to the non inverting terminal of OPAMP, which is a low pass filter. For the gain adjustment a 100 k preset is connected in between the output and inverting terminal. A 10 K preset is used for adjust the offset voltage. The amplified signal is then feed to the non inverting terminal of the summing amplifier for make the accurate value. Then the output voltage of the summing amplifier is inverted in nature hence the inverting amplifier is used here for adjust the polarity.

The signal from the amplifier is analog on nature and it is then converted into digital form by using an ADC .The ADC 0804 is used for this purpose. The successive approximation method is used here for the conversion. The output of the amplifier section is feed to the 6^th pin of the ADC. The digital output is obtained in the 11^th to 18^th pin of ADC, which is then given to the microcontroller for further processing. The 89C51 is an 8 bit microcontroller which works under the base of a program. When microcontroller executed the various parameters is displayed on the LCD. The relay driver and buzzer driver sections are works under the control of microcontroller.

9.    PCB FABRICATION

LAYOUT DESIGN

From the schematic diagram, the layout is prepared on a graph paper according to the rules and regulations of PCB layout In the 2:1 scale. If necessary we can acquire the help of a computer tapes. In double sided PCB's the track side and the component artwork are prepared on separate sheet using black colored tapes. In computerized PCB designing, suitable software is used to design the PCB's. here we use the computerized PCB designing with the help of pen plotter the artwork is transferred to the paper 2:1 scale.

PHOTOGRAPHIC REDUCTION

The artwork is photographically reduced to 1:1 scale in process camera. In the orthochromatic lithe film, the artwork is photographed and the negative film is taken for the PCB fabrication in photographic method.

BANKING OF LAMINATE

Require size of copper clad sheet is cut from the copper clad laminate. While cutting of laminate 10mm clearance is provided.

DARK ROOM PROCESS:

PHOTO RESIST COATING

Photo resist is a liquid formulation, usually bromide compounds, which is very sensitive to UV light, if causes polymerization and changes its solubility in solvents. The cleaned copper clad sheath is dipped in an oven for 10 minutes.

EXPOSING

The photo resist coated board is exposed to an UV light source through negative film obtained by photographic reduction. The time taken for exposing

 is 2.45 minutes. During exposing film and copper sheaths are intimate contact. Vacuum pump expose pump expose machine is used for exposing. For getting good quailing PCB after exposing, we should follow the cleaning procedure strictly. After exposing you can develop the PCB.

DEVELOPING

During exposure, the photo resist coated board has undergone selective polymerization. Thus the circuitry positions where conductors, the resist unaffected. This unaffected resist is soluble in developer and polymerized resist is insoluble. After this the board is dipped in photo resist dye and extra coating. Then the board is washed in running water.

ETCHING

For removing copper from the non-polymerized part of the bourdon is fed to the etching machine. The chemical used for etching is ferric chloride and water having specific gravity 1.2 after 3 or 4 minutes this is rinsed in running water. Over etching will case under cutting. Then the paths are short circuited, we can remove that one. That means if any two conductor paths are circuited, we can remove that over. CLEANING The Contaminates like oil, Oxides are removed by washing the copper clad sheath with 5% Hcl and scrubbed with pumice powder. If the water is uniform without any brake, then the surface is full of dirt you can use sandpaper for cleaning and then washed with water.

DRILLING

The holes for mounting the components are drill machine having a  maximum speed of 20,000 rpm. At the time of drilling, the diameter of the drilled holes proportional to the components, which mounted at that hole. That the drill bit is selected bit is selected according to the component.

TIN PLATING

The tin plating is given to the PCB for preventing the formation of oxide coating. This also use a special attraction to the component mounted PCB. Instead

of thin we can also use silver or other materials, which has the same property of this metals, for the planning of PCB's.

SOLDERING

The components are bent in the correct dimension, inserted in to the hole and Soldered.

.

10.     PCB LAYOUT

PCB SIDE

FIG 10.1

PROCEDURE

1.      Clean the objects to sterilized and place it inside the sterilization'  chamber.

2.      Close the gasket properly.

3.      Switch on the main supply.

4.      Select the temperature cycle by using H or C keys.

5.      Set the sterilization time and dry time.

6.      Press the menu button for starting sterilization.

7.      Wait until the buzzer is activated.

8.      Open the gasket and move out the sterilized objects.

11.     HARD WARE AND SOFTWARE REQUIREMENTS

COMPONENT                                    NUMBER OF ITEMS            

RESISTOR                                                                             6

RESISTOR ARRAY                                                             1

TRANSFORMER                                                                  1

PRESET                                                                                  2

CAPACITOR                                                                         10

2-PIN POWER CORD                                                          1

20PINBASE                                                                           1

DIODE                                                                                   2

ZENER                                                                                   1

TRANSISTOR                                                                       2

CRYSTAL                                                                              1

RELAY                                                                                  1

MICROCONTROLAR 1 C                                                   1

REGULATOR 1 C                                                                 1

OP-AMP                                                                                 1

ADC                                                                                       1

LCD                                                                                        1

LM35                                                                                      1

BUZZER                                                                                1

SWITCHES                                                                            1

12.        STERILIZATION TIMINGS

·         Laundry: 250°F (121°C) for a minimum of 30 min.

·         Trash: 250°F (121°C) for at least 45 minutes per bag.   Size of the autoclave and of the bags greatly effect sterilization time.  Large bags in a small autoclave may require 90 minutes or more.

·         Glassware: 250°F (121°C) for a minimum of 25 min.

·         Liquids: 250°F (121°C) for 25 minutes for each gallon.

·         Animals & bedding: Steam autoclaving not recommended (sterilization time required would be at least 8 hours).  Incineration in an approved facility is the recommended treatment of these wastes.

13.        PRECAUTIONS

1.      Ensure that the power plug is connected properly.

2.      The object to be sterilized should withstand the temperature inside the chamber.

3.      The gasket should be properly closed to avoid leakage of steam and losing of pressure.

4.      The gasket should not be opened while the process is going on as a high pressure is present inside.

5.      Ensure the water level is above the coil before sterilizing and never switch on the sterilizer if water is not present which may damage the coil.

6.      The sterilized objects should be removed with utter care, which should not be touched by hand.

7.      Switch off the device after the sterilization is complete, do not leave the device powered.

14.      FLOW CHART

15.      ADVANTAGES

·   We can  easily operate this instrument. There is no need of  external  

   Power     to drive it. It also turned ON and OFF automatically.

·   Highly reliable and small in size.                            

·   It is highly sensitive  as compared to the normal  sterilizer.

    

16.   DISADVANTAGES

·         If any fault occurs to the system, maintenance cost   would be high.

·         Trouble shooting is difficult.             

17.  CONCLUSION

            Our sterilizer is an automatic device which is controlled by a microcontroller 1C. So the operator will just have to switch on the device and set the sterilization time and dry time and the mode in which it is to be operated, i.e. in hot cycle or cold cycle. When the sterilization procedure gets completed the display indicates the ending of sterilization and a buzzer is activated, so there is no need of continues verification of the process.

         Our project tabletop sterilizer has been made to a success by the restless efforts and hard works of the project team members and with the whole hearted support from all the staff and students of the institution

              

                                                                                                         

18.     FUTURE SCOPE

              By using this smart sterilizer we can sterilize the medical equipments automatically and these are done in an automatic manner. Its main objective is to avoid the presence of micro organism we know that, due to micro organism there may arise syndroms. These an be prevented by using this system.

APPENDIX

MICROCONTROLLER PROGRAM

#include <reg51.h>

#define uc unsigned char

unsigned int tempdata,settemp,temp;

void lcd_com(uc command_word);

void lcd_data(uc value);

void display(uc *s);

void lcd_init();

                                                                

sbit rs=P1^6;    

sbit en=P1^5;

sbit start=P1^1;

sbit oe=P1^0;

sbit eoc=P1^2;

sbit inc=P0^1;

sbit ok=P0^2;

sbit cancel=P0^3;

sbit dec=P0^4;

sbit heater=P1^3;

sbit buzzer=P1^7;

void delay(unsigned int y);     

void converts(unsigned int g);

void main()

{

P3=0xff;

P2=0;

P0=0xff;

lcd_init();

lcd_com(0x80);

display("Smart Sterilizer");

lcd_com(0xc0);

display("Set Temp:");

//while(1)

//{

//   led=0;

//   delay(500);

//   led=1;

//   delay(500);

//}

while(1)

{

if(ok==0)

  {

   lcd_com(0xc0);

   display("Set Temp:       ");

   while(ok==0);

   delay(100);

   while(ok==1 && cancel==1)

   {

   if(inc==0)

      settemp++;

             

   if(dec==0)

      settemp--;

              if(settemp>=100 || settemp<=10)

                 settemp=28;

              converts(settemp);

              delay(300);

   }

  }

oe=1;

eoc=1 ;

start=1;                //start of convertion

delay(1);

start=0;

delay(5);

start=1;

while(eoc==1);

oe=0;                   //read data

delay(5);

tempdata=P3;

delay(5);

oe=1;

temp=(tempdata+100)/4;

converts(temp);

//converts(tempdata);

if(tempdata>=settemp)

{

  buzzer=0;

  heater=1;

  delay(400);

  

}

else

{

buzzer=1;

heater=0;

}

}

}

// lcd..............................

void lcd_init()                          

{

  lcd_com(0x38);

 delay(1);

 lcd_com(0x0c);

   delay(1);

 lcd_com(0x01);

  delay(1);

 lcd_com(0x02);

 delay(1);

 return;

}

void lcd_com(uc command_word)                 

{

rs=0;

P2=command_word;

en=0;

delay(1);

en=1;

delay(1);

return;

}

void lcd_data(uc value)        

{

rs=1;

P2=value;

en=0;

delay(1);

en=1;

delay(1);

return;

}

void display(uc *s)

{

while (*s)

  {

  lcd_data(*s);

  delay(1);

  s++;

  }

  return;

}

///////convert..............

void converts(unsigned int g)

{

unsigned int x;

x=g/100;

x=x+(0x30);                                                                 

lcd_com(0xcc);

lcd_data(x);

g=g%100;

x=g/10;

x=x+(0x30);

lcd_com(0xcd);

lcd_data(x);

x=g%10;

x=x+(0x30);

lcd_com(0xce);

lcd_data(x);

return;

}

// delay.............................

void delay(unsigned int y)

{

    unsigned int k,h;

  for(h=0;h<y;h++) 

   

  for(k=0;k<=250;k++);

  return;

}