Position: The content of this page is about the conveyor belt weighing system Based pc/micro controller.
The conveyor belts are one of the most important techniques used for transferring commodities in the industries. Its obviously going to add to the utility of conveyor belts if the commodities are going to be weighed while they are going on conveyor belts. Most of the earlier methods used micro controller based weighing systems and they were low capability devices. The problem with the techniques was that hardly any database management was possible. However micro controllers was a low cost option for such applications for a considerable duration. With reduction of cost of personal computers, they can be used as viable alternative to the micro controller system for these types of applications. Additionally, the huge computational power and speed of the recent PCs, their high level language programming interface and advanced IO interfaces, enhanced secondary memory handling capabilities make them preferable over the micro controller based systems. The next generation weighing systems were developed using ISA (INDUSTRY STANDARD ARCHITECTURE) interface. ISA interface proved to be quite successful upon the micro controller based systems as the interaction with computer was simplified. ISA still had many drawbacks like it didnt had plug and play feature and the word length was also less. They have the present generation slots called PCI (peripheral component interconnect) which has a higher bandwidth and also provides plug and play facility. PCI provides the forward and backward compatibility means that even an old ISA card can be used in modern PCI slots with some modifications. PCI provides much higher rate of data transfer accordingly on the same PCI slot. So we decided to make a conveyor belt weighing machine system using PCI interfacing to provide high speed system along with user friendly interface. Thus we tried to implement the project with the aim of achieving higher accuracy, faster weighing system and a user-friendly database management system.
Block Diagram
The following block diagram implements the task of measuring weight on the conveyor belt.
Fig 2. Block Diagram
The weight to be measured by the load cell is dropped on to the moving conveyor belt with the help of hopper arrangement as shown. The weight to be measured is applied to the load cell. The load cell is a transducer that converts any physical or non-electrical quantity into electrical quantity. The output of load cell is in mill volts and needs to be amplified as this quantity is to be transmitted over long distance attenuation. The amplifier used here is AMP-01FX. This amplifies signal acts as an input to an analog to digital converter AD676. It is a multipurpose 16 bit parallel output analog to digital converter which utilizes a switched capacitor/charge redistribution architecture to achieve a 100kbps conversion rate(10 microseconds total conversion time).As parallel transfer is desired PCI is being used also PCI is quite versatile and the Present PCs have PCI slots mounted on them. 8255 is a general-purpose programmable I/O device designed for the use with microprocessor system. The programmable ports for data transfer are provided by 8255, which needs no external logic to interface peripheral devices or structures, but programmed by the weighing software. Hence the PCI8255 add on card is used to read the digital date by the computer and it can be read and processed by using a program in C.
D.C MOTORS
D.C motors are seldom used in ordinary applications because all electric supply companies furnish alternating currents. However, for special applications such as in steel mills, mines and electric trains, it is advantageous to convert alternating current into direct current in order to use d.c motors. The reason is that speed/torque characteristics of d.c motors are much more superior to that of a.c motors. Therefore, it s not surprising to note that for industrial drivers, d.c motors are popular as 3-shunt-wound and compound-wound. The use of a particular motor depends upon the mechanical load it has to drive.
Motor specification:
1 horsepower
Dimmer specification:
A dimmer, which consists of variable inductor, is used to vary the speed of conveyor belt. The type of dimmer used here is manually dimmer (upto 4 to 6 A), which has a capability to drive D.C motor efficiently.
Load Cells
An electronic instrumentation weighing system consists of a number of components to perform a measurement and record the result. A transducer is a device the converts the physical or a non electrical quantity into an electrical one. The electrical output can thus be measured by standard method. A force or weight can be measured by a load cell. The load cell is a short column or a strut with resistance wire strain gauges bonded to it. The measured, in this case is the weight and is applied to the column thereby producing strain. The force is first detected by the column and is converted into strain which is a mechanical displacement. The greater the weight, higher is the strain on gauges, this strain changes the resistance of the strain gauges resulting the output in electrical form i.e. voltage. Hence in this case it takes two processes to convert an input into an analogous output
Amplifer
Need for amplifier
The output from load cell is in the range of millivolts, which cannot be transmitted for a long distance without avoiding attenuation. So as to facilitate successful transmission we need to amplify the output of the load cell. The choice of amplifier depends on various factors like the range of gain, fidelity, gain-bandwidth product, negligible offset voltages, low bias currents and excellent noise characteristics. We are using AMP01fx instrumentation amplifier because of it provides large range of gain and excellent signal reproducing capabilities.
Process of Digitization
The A/D Conversion is a quantizing process where an analog signal is represented by equivalent binary states. Analog to digital converters can be classifies into two general groups based on conversion techniques. One technique involves comparing a given analog signal with internally generated equivalent signal. This group includes successive approximation and flash type converters. The second technique involves changing an analog signal into time or frequency and comparing these new parameters against known values. This group includes voltage to frequency converters and integrated converters.
Analog to Digital Converter
Computer reads data in the digital format, so it is necessary that the analog output of the amplifier is to be converted to digital. So we require an analog-to-digital converter as an interface between the amplifier and the PCI8255 card. ADC‘s provide different resolution like 12 bit, 16 bit and so on. We are using AD676 which provides 16 bit resolution i.e. the input voltage range is divided into 2 steps (65535) giving higher level of accuracy as 1 6 compared to other ADC‘s. Speed of operation is a very important factor in our project as the load to be measured is varying continuously on the conveyor belt. Therefore even a small delay on the ADC side can lead to erroneous results and AD676 takes around 8.5 s for one analog-to-digital conversion.
PCI 8255 card
Need for Speed and data transfer at higher bandwidth is the result of the development of new technologies like PCI (Peripheral Component Interconnect). In our project we have used PCI 8255 card manufactured by Decision Computer International. We are using it as an interface between the ADC (Analog to Digital Converter) and the Computer. This card has many salient features like
32 bits PCI bus with Plug and Play (PnP) features.
Programmable I/O control functions.
Up to 48 I/O lines.
Maximum of 10 MHZ counter rate.
The PCI bus 8255 adapter provides total 6 digital I/O ports; each I/O port contains 8 I/O lines, and can be set either input or output by the user‘s program. The signal assignments of PCI bus 825 5 adapter is designed as standard configurations, so that it can be used to connect to the 8255 terminator board for several weighing applications. The card can be very easily controlled by using a simple program and the I/O addresses of the ports. Once the base address is obtained then we can find the address of other I/O ports as
Base + 0 : Port 1A input/output buffer.
Base + 1 : Port 1B input/output buffer.
Base + 2 : Port 1C input/output buffer.
Base + 3 : Port 1 control register.
Base + 4 : Port 2A input/output buffer.
Base + 5 : Port 2B input/output buffer.
Base + 6 : Port 2C input/output buffer.
Base + 7 : Port 2 control register. Project Guide:
DR. K M BHURCHANDI
Projectees:
NAMISHA AGRAWAL
POONAM JATTEWAR
SHIKHA JEJANI
PRACHI JOSHI
SACHN SATHE
APEKSHA DHONGDE
