Digester Version 2: More on the electrical system

The HMI panel This is a view of the HMI panel used on the new digester. It is a fairly inexpensive piece of hardware, and offers a touch screen LCD display and a membrane keypad. When the digester is in operation, this LCD shows all the operating parameters and logged data channels. Numeric entry is possible on the keypad for temperatures and runnign times.
Mounting this panel took me a very long time. Ordinarily, this type of stuff would be mounted on the front of a cabinet, and it comes with a nice cardboard outline that you just trace onto the panel and cut. However, for the digester, the panel had to be rated for outside exposure. This means I had to install it inside a box. Furthermore, I had to be able to get at the wiring inside, as several communications lines pass through this box on their way someplace else.

Inside the HMI panel The answer was mounting the HMI on a hinged section that can be swung out of the way to get at the wires inside. This photo shows the control panel, swung open, revealing the wires underneath. When shut, the box is NEMA-4X, but when open it allows complete access for wiring and HMI configuration. I chose transparent front boxes for this equipment so that the operator can see the system overview screen without opening up the box. This control panel is located near the valves and the effluent line, the intent being to mount it nearest all the action. To the left of this is another thermocouple input panel, which talks over RS-485 back to the main PLC cabinet.

The AC contactor panel Here is an unlabeled, close up view of the AC enclosure. Circuit breakers on top, contactors in the center, wire distribution out the bottom. Lower right hand side is the main switch, 120V aux outlet breaker, and pump motor transformer. Due to design constraints, the 24V DC is in the lower left hand corner, immediately adjacent to the 240V AC terminal strips.

Lovely wiring on the control panel There is something really nice about good rows of happily organized and zip-tied wires. This photo shows the back of the AC control panel. At the bottom are the illuminated pushbuttons used to feed and mix the tank, and the top are the auto/off/manual switches for the pump contactors.

PLC Enclosure inside Here is another view inside the PLC enclosure. It appears to be a lot of hardware, but it is tough to meet specifications when they are always changing.