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) arranged at a distance.
That means, the operator cannot press the pushbuttons with one hand. At times, there is a tendency on the part of operators to latch one of the pushbuttons by other means and operate the machine with one hand and adjust work-piece or tools with the hand.
The pushbuttons must be pressed within a very short time, say one second to get the anti-tie down feature. A ladder program to implement this control requirement taking a lamp as the representative output device.
Programmable Logic Controllers and Programming Concepts
With Electrical, Pneumatic, and Hydraulic Applications
Fluid Power Educational Series