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Remote Sensing and Control System (Graduation Project -2001) |
1- Introduction
Project under study is the collection of sensors, which would monitor the environment and transmit this data remotely to the computer. We could call this remote sensing. Here we also look at how we can not only monitor remote environment but also control some factors by using controllable devices such as cooling fans, lights, identification horns etc. In short we have to design a system in which data from different sources are combined, digitized and transmitted over a single channel. such a system is know as Data Acquisition (DA) system.
DA system vary widely in scope and demand, depending its properties of data itself (no. of channels dynamic range, frequency content) and the application requirements. The application requirements include resolution and accuracy as well the environment in which the system resides. At the lower end, a single channel of recording with direct readout may be needed for applications such as chart decoder or meter. At the upper end, complicated multi-channel systems may be needed, in which data will be sampled, processed and sent to a central computer.
A particular system shows various transducers connected to the input conditioning unit. Depending on the transducer signal, input are then amplified for offset or filtering. The gain of the input conditioning circuits may be controlled by a central processing unit to set to the proper level. The input signals are then routed to ADC (analogue signal to digital signal) that can be used by the CPU (central processing unit). The CPU controls, records, analysis and reports the data it acquires.
1.1 DESIGN PREFERENCES:
| Analogue Sensor Amplification / Limiting | The system to be designed in this project consist of eight analogue sensors and 3 digital sensors, and their data to be read directly from the computer. It can switch on and Off 3 to 7 output devices depending upon the output circuit construction. Depending on the transducer signal, input are then amplified for offset or filtering. |
| Multiplexing and Digitization | Reading Analogue signals through a computer we require ADC. When connecting number of analogue signals to the computer, it is very much impractical to use an ADC with each of them. This gives way to an idea of having one ADC and digitizing each of analogue sensor at a time and then moving on to another. For this we need a analogue switch to select one analogue signal at a time and take it to input of ADC. Such an analogue switch is known to be an analogue multiplexer. |
| Timing Circuits & Serial Conversion | The timing circuit controls the start and the ending of time function for each sensor, which means it introduces a delay variable factor to the circuit so as to allow analogue signal to settle down, converted to digital and transmitted successfully before moving on to the other. When connected to the computer the timing circuit act like a communicator with the computer and forms its own customized protocol. It is also required that the data should be in series to be transmitted. Which means any data that is in parallel should be sequenced in such a way that serial transmission is possible. |
| Computer Interfacing and Programming | The simplest technique is to use the computer interface through the parallel port of the computer. Its not only easy to program but saves a lot of time and money. However, a buffer circuit is essential to prevent loading. Structural or object oriented programming languages with Assembly-language support could be used to display data in a graphical mode at the workstation. |
The project uses all TTL logic devices. The information display rate in this project would considerably slow depending upon the speed of analogue multiplexing and serial transmission.