This PL-Sim unit simulates an electropneumatic exercise panel. It incorporates three double-acting air cylinders (A, B and C), each driven by a 5/2 double solenoid valve. The solenoid valves are of the electrical type, each having both a positive (A+, B+ and C+) and negative (A-, B- e C-) solenoid. 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 hereby allows the compressed air to flow into the positive chamber of the cylinder and flow out through the negative chamber. The piston, by advancing from the negative limit switch, will perform positive travel and stop at the positive limit switch.
On the other hand, if the negative solenoid is energised,it again toggles again the solenoid valve status so that the compressed air can now flow into the negative chamber and flow out from the positive chamber. The piston, by retracting from the positive limit switch, will perform negative travel and stop at the negative limit switch.
A solenoid, if energised, toggles the status of the solenoid valve; as it is a double solenoid valve (bistable) it remains in the toggled position, even if the solenoid is de-energised, until the opposite solenoid is energised. If the two solenoids are energised simultaneously this results in an indefinite status of the solenoid valve and an inaccurate position of the cylinder. This malfunction should be avoided when programming a PLC. On the other hand, if a solenoid is energised when the opposite solenoid is still active, the solenoid valve status is not toggled until the active solenoid is de-energised.
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 these push buttons the solenoid valve status can be toggled and the cylinder can perform positive or negative travel.