ade
Member
Ant-plc-man said:CAn anyone tell me the characteristics (or where to find them?) of both analogue and digital signals.
ANALOG
In application, let say you have a pressure transmitter with 0-300 PSI input, and 4-20 miliamps output. You connect the output of the pressure transmitter to the PLC analog input module, after some codings in the PLC program, the 4-20 miliamps becomes (say 8 bit) 0-255(decimal) and stored in the data table represented by 8-bits. In analog value, you have many numbers, in fraction of 1, you will have 255 unit of fraction. So in the analog term, you have "in-between" value between 0 and 255, 0-300psi, 4-20mA.
DISCRETE
Again, in application, you have a pressure switch (fro example) that calibrated at 150 psig to pick up the contact either ON or OFF. Then you connect the pressure switch to the PLC Discrete Input Module, and after some codings, the physical input then represented by a single bit in the PLC memory, these single bit can only either ON or OFF. There is no "in-between" value in the discrete term, the only value is ON or OFF, 1 or 0, High or Low.
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Sorry if there are some mistakes
-ade-