What symbol is used when looking for a "0"?

The symbol used when looking for a "0" in programmable controller systems is represented by brackets. In the context of programming and control logic, square brackets typically indicate a range, a condition, or a specific condition set that the system should recognize. The representation '] [' can signify that the system is looking for a zero or a specific condition where two states or values are being evaluated. This notation is crucial in programming logic as it helps define parameters or constraints within which a particular operation must occur, especially when dealing with conditions related to data inputs or state values.

The notation in this case ensures that all the logical operations surrounding the detection of a zero are unambiguous and clear, making it easier for one to interpret or program in the context of automation and control systems. Understanding these symbols and their meanings is key to effectively working with programmable controllers.