Identifying Device in Pneumatic Actuator Controller Diagram Labeled as PLC

I am a graduate Aerospace Engineering student. I need to wire a pneumatic actuator's controller and a magnetic position sensor for a small part of my research. I received a connection diagram from the company making the controller, and there is a relevant video showing the procedure on YouTube. Since I, unfortunately, don't remember anything from my electrical course years ago, I don't know what a particular component in the video is called. The connection diagram says PLC, but there does not seem to be any 'PLC' in the form I am vaguely familiar with, nor is there any programming involved in the video. 
Video - https://www.youtube.com/watch?v=5lFFg6-doK0 (from 0:05)
What is that device in the center called? It just seems to transfer i/p-o/p 
I have also attached the connection diagram I received. 
Thanks in advance!!
 

Hi Aadhy-The mystery device (PLC) is a Programmable Logic Controller.The "S2" appears to be a device that allows you to control a pneumatic cylinder similar to the way you would control an electrically-operated linear actuator.  Pneumatic cylinders are most often used at their full stroke, but the S2 applies feedback to they can be stopped and controlled anywhere along their travel using an analog control signal. -Rick

The PLC is not shown in the video.  Looking at your diagram, the PLC output is wired to the "Command" input terminal, and in the video this terminal has an orange wire labelled "Analog" attached to it going off the right of the screen.From the diagram it would seem that the command terminal needs  an analog signal of 0-10V or 4-20mA (both of which are common control ranges).  This could come from a Progammable Logic Controller (PLC) output (as in your diagram) or even a potentiometer for manual control.  Were this actuator to be used on a machine, the PLC would output a control signal based on where the actuator needed to be positioned, possibly with feedback from sensors on the machine.   You just feed the S2 command terminal with a signal corresponding to where you want it to position the actuator.  For example, if you wanted to position the actuator at half-way, you'd put a voltage of 5V on this wire (assuming a 0-10V control input.  I'm not sure how you'd set it for 0-10V or 4-20mA input, but the datasheet should tell you.The PLC is just shown as having an output, confusing if you are not familiar with them.  In practice it would need (usually) 24V power and inputs from sensors to enable it to make decisions.But PLCs are very handy things and certainly worthy of more study if you're doing this sort of stuff.

Thank you for your reply. The component I was asking about is apparently called 'terminal blocks on DIN rail'; as an electrical person, you probably don't even consider that as a 'component'. It was only after I knew the name of it that I came to know its just a terminal to connect wires, my bad. 

Yes, it took me watching the video very closely to notice they do make a PLC connection and that the PLC is used only as an analog input here. At first, I was very lost with what the PLC was even doing there, considering it is not even taking sensor output as input. The only thing I knew about a PLC was that it takes inputs, performs some logic, outputs. 
The output from the sensor is going to the controller, which will be connected to a PC with their software, where I can input parameters to control position. This is actually a very small part of the experimental set up for my research, but sure, PLCs seem interesting. Thanks for answering!