The scan refers to the process of reading inputs, executing the program, & updating the outputs.
A processor can read an input if it is not faster than the scan time.
Some PLCs give software instructions that allow you to interrupt the continuous program scan in order to receive an input or update an output immediately.
Function of Pulse Stretcher
- A quick-response module, sometimes known as a pulse stretcher, can be used to interpret extremely fast inputs.
- This module extends the signal such that it can last for at least one full scan.
- To avoid losing pulses, this form of interface requires that the signal not occur on more than every two scans.
- A pulse stretcher is best suited for applications requiring very fast input signals.
- To read a large number of pulses faster than the scan time, a high-speed pulse counter input module might be utilized to convey the data to the CPU.