PC BASED DATA LOGGER (12-BIT 8-CHANNEL) AIM: The aim of the project is to design a 12 channel data acquisition system to monitor and record continuously varying process parameters and to develop an ADD-ON card circuit and software program in Visual Basic to see various data in personal computer. The essential functional operations of data acquisition systems are Handling of analog signals. Making the measurements. Converting the data to digital form and handling it, and Internal programming and control. The Block diagram in Fig-1 shows the proposed circuit model of an ADD-ON card. It uses the popular bus interface technology ISA (Industrial Standard Architecture). It supports 8-bit and 16-bit data length. We proposed to choose the former for its simplicity. The I/O address for this card ranges from 300H to 31F which is free Address range of every PC to have no conflict with other Devices. It is proposed to handle 8 analog I/Ps and 24 digital I/Os. The analog I/Ps are multiplexed (8 to 1) to provide single I/P channel for a 12-bit ADC (AD574A). The analog section and digital section of the card can be handled by two PPI devices (8255) I/O mapped to PC using some chip select logic. Using a buffer as shown in the figure can enhance bi-directional data flow. Housing the card inside PC, size of card and external interface should be taken care of. Extra Boards such as signal conditioner relay or LEDs can also be constructed for external interfacing. Software should be developed for proper usage of the card in accordance to the Plant requirement or any other similar criteria. We proposed to use Visual Basic for its ease in programming flexibility. Analog Signals ADC Analog B 12-bit Mux D0-D7 u A f 9 –Pin f D Connector e B PPI-1 r I S C A S L O A T I/O Signals A0-A9 B PPI-2 Chip Select C logic 25 –Pin D Connector Figure-1:- Functional Block diagram of an 8-channel Data Acquisition Add-On card model.
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