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1.4 MILES of Wire Saved Through Innovative PLC Architecture

... and over 800 electrical and 40 instrument air connections!

The field wiring for our customer became very complex because they wanted verification that each of the twenty actuated valves is in the correct position.  Also, the system is pre-programmed to allow up to four additional greensand filter units through a HMI touchscreen. If the control panel with the Allen Bradley PLC is only 10 feet from the first tank, fully outfitted, this control architecture would save over 2.8 MILES of wire, 1600 electrical terminations and 80 pneumatic connections and countless hours of wiring and troubleshooting!

Fieldbus Distributed I/O Module Blocks Installed n Each Greensand Filter Unit

One of the above fieldbus distributed I/O module blocks are installed on each of the four greensand filter systems for a local brewery.  This efficient architecture:

  • Requires only two cables (Ethernet and low voltage Power) from each block to the main control panel eliminating point-to-point wiring from each system to main control panel
  • Eliminates over 840 sources of potential errors by mechanical contractors during field installation (800 electrical terminations and 40 pneumatic connections)
  • Eliminates enclosures with a total of over 40 penetrations
  • Reduces the PLC inputs and outputs by 40, thereby reducing the size of the main panel
  • Is rated IP67 (Dust tight and submersible to 1 meter)
  • Operates at 24 VDC
The fieldbus system we employed is the PLC distributed I/O system (remote I/O modules) that is connected to the PLC using network called fieldbus. Typical fieldbus examples: Profibus, CAN, Modbus, ControlNet, DeviceNet, Ethernet I/P. At our customer, Res-Kem used  Ethernet I/P (I/P=Industrial Protocol) fieldbus. Each block must have communication adapter that is connected to the PLC network. At our customer, the Ethernet Adapter connected to the panel Ethernet switch. In addition to I/O blocks, the vendor Res-Kem uses, has solenoid blocks that are acting like digital outputs and are attached to the I/O system. Each block (fieldbus system) is powered from 24 VDC power supply providing power for backplane.
 
Greensand Filters During Factory Testing Showing Location of Each Fieldbus Block
Greensand Filters During Factory Testing Showing Location of Each Fieldbus Block

Normal practice is to add an electrical enclosure which has solenoid valves to operate pneumatic actuators and electrical terminal blocks for the limit switches and solenoid valve.  At the customer's site, each electrical enclosure needs to have point-to-point wiring to the main panel with the PLC.

 
Typical Solenoid Panel WITHOUT Limit Switch Terminations
Typical Solenoid Panel WITHOUT Limit Switch Terminations

More About Fieldbus:
Fieldbus is an industrial network system for real-time distributed control. It is an efficient way to connect instruments in a manufacturing plant.

From Wikipedia, "A complex automated industrial system — such as manufacturing assembly line — usually needs a distributed control system—an organized hierarchy of controller systems—to function. In this hierarchy, there is usually a Human Machine Interface (HMI) at the top, where an operator can monitor or operate the system. This is typically linked to a middle layer of programmable logic controllers (PLC) via a non-time-critical communications system (e.g. Ethernet). At the bottom of the control chain is the fieldbus that links the PLCs to the components that actually do the work, such as sensors, actuators, electric motors, console lights, switches, valves and contactors."
 
For Additional Information:
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Greensand filter bulletin

Posted on September 13, 2013 by Tom Dupnik | Tags: , , , , , , ,

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