How a PLC can be used to handle an analog input? Justify.
1 Answer
Answer :
Diagram:--
Explanation:
For analog operation, the level of a PLC input signal is sensed by an analog input module, like in a data acquisition system when input parameters may be the analog values of temperature or pressure. Similarly, the output may be an electrical signal controlling the current through a system which can operates positions between ON and OFF.
Analog PLC systems are of two general types: the BCD and the straight numerical. The BCD is called multi-bit type. The inputs include data from devices like thumbwheels, encoders . BCD codes are fed into the PLC input module from the thumbwheel output. Other possible BCD-type inputs are barcode readers and encoders.
Similarly, the output may be a digital display, various position actuators and sow" motors.
A straight numerical type of module is used for a large variety of input devices like a potentiometer inputs a linear varying electrical value. Other inputs are thermocouples, strain gauges and signal generators which generate electrical signals.
The method in which these analog inputs are handled is of course similar to a microprocessor. First the data is to be converted into digital signals and then processed by the PLC
On the output side, the output data from the PLC are converted into analog data and given to the output device. Figure shows lac block diagram of this process.
Initially the data handled is in BCD, and then as soon as it reaches the PLC, it is first converted into machine code and then the necessary control signals are generated to the output module.