If you are developing a system with touchscreens, it is important to pay attention to good human factors.  First, I always develop with the idea that the operator's finger will be the same size as my thumb (some of the guys I've worked with have had huge fingers).  A very important standard to maintain is requiring two touches for any field action.  In other words if you need a pump to start, require the operator to select the pump on the screen and then touch a separate location to start or stop the pump.  Usually we handle this with popup screens that will handle all the start stop functions.  Selecting the pump, motor or other object on the screen will simply popup the control window.