In two-hand safety operations in dangerous industrial operations, such as a pneumatic press, the hands of an operator must be engaged for safety reasons. This condition is usually achieved by arranging two pushbuttons (Say, PB1 and PB2) at a distance.
That means the operator cannot press the pushbuttons with one hand. At times, operators tend to latch one of the pushbuttons by other means, operate the machine with one hand, and adjust the workpiece or tools with the other hand.
The pushbuttons must be pressed within a short time, say one second, to get the anti-tie-down feature. A ladder program to implement this control requirement by taking a lamp (Q100.1) as the representative output device.
Programmable Logic Controllers and Programming Concepts
With Electrical, Pneumatic, and Hydraulic Applications
Joji Parambath
Authored by
Joji Parambath
Author
Fluid Power Educational Series