This PL-Sim unit simulates the last electropneumatic exercise panel. It incorporates three single-acting air cylinders (A, B and C), each driven by a 3/2 single solenoid valve. Solenoid valves are of electrical type, each having a positive (A+, B+ and C+) solenoid; return is of mechanical spring type. All cylinders are provided with negative (a0, b0 e c0) and positive (a1, b1 e c1) limit switches. The limit switches and solenoids are fitted with status LEDs. A LED ON status indicates that a limit switch has been energised or a solenoid has been enabled. Solenoid valves have manual override control buttons.
Assuming that the cylinder is at the negative limit switch, the positive solenoid, if energised, toggles the solenoid valve status and allows the compressed air to flow into the positive chamber of the cylinder. The piston, by advancing from the negative limit switch, will perform positive travel and after pressing the spring will stop at the positive limit switch.
On the other hand, the solenoid, if de-energised, it enables the spring to toggle the solenoid valve position, returning it to a stable position. The compressed air can now flow out of the positive chamber. The spring will retract the piston from the positive limit switch; the piston will then perform negative travel and stop at the negative limit switch.
When the solenoid is energised, the solenoid valve status is toggled; as it is a single solenoid valve, it remains in the toggled position while the solenoid is activated. By de-energising the solenoid, the solenoid valve returns to its original position.
The manual override control buttons, at the side of each solenoid valve, allow switching into manual mode and are therefore useful when tuning a program. By pressing this button the solenoid valve status can be toggled and the cylinder can perform positive travel. By releasing this button, the solenoid valve toggles again and the cylinder can perform negative travel.