Here's a good example of our PLC simulators used on an Allen Bradley SLC-500 trainer.  I built this unit for a customer that does automation training.  This concept is easily adaptable so if you're interested in something like this then feel free to contact me.

The demo stand consists of an Allen Bradley SLC-500 with a power supply (1746-P1), CPU (1746-OS501), an 8 point input card (1746-IB8), an output card (1746-OB8) and an analog input/output card (1746-NIO4V).  The plc simulators are mounted on the din rail below.  The digital input simulator (DI-8-UM) controls the inputs to the input card.  The analog input simulator (AD-4-V-UM) provides the signals for the analog inputs.  It's all mounted on a light weight A-frame that folds flat for easy travel.  The PLC stand also has a rubber lining on the bottom to prevent slipping while the PLC is being used.