Tuesday, June 29, 2010

Troubleshooting PLC SCADA systems.

This is in reply to a discussion on CR4 where the commentor suspected sensor wiring method to be root cause of extended troubleshooting time. My reply below...

Actually it does not matter if you have hardwired, Modbus, Devicenet or wireless sensors as far as troubleshooting time goes. (although any of the above can add to number of problems to be found. Like Modbus communication going out.)

The two primary factors in troubleshooting with a PLC is training and documentation. Using a PLC, it typically takes 5-10 minutes for a properly trained technician with discriptored ladder logic and an electrical layout diagram, to find a problem, no matter how complex the system. Time to fix varies on actual problem found.

Items that can increase troubleshooting time in order of most negative effect are ...

  • Lack of proper training.
  • Lack of proper PLC program documentation.
  • Over complicated PLC ladder logic.
  • Lack of electrical layout and schematics.

System Designs in order of most timely to troubleshoot are ...

  • DCS (Mostly proprietary and designed for only OEM to use.)
  • SCADA (Often proprietary, non-user friendly and training deficiencies. Seek Wonderware® and Factorytalk® training.)
  • PAC (Ladder Logic easy, but function block diagram is not always, structured text is a more complex computer programming language.)
  • PLC (Ladder Logic, easy for electricians and mechanics too if taught properly.)

The bottom line is that all the above systems could be easy (quick) to troubleshoot if one is constantly trained, the system is well documented and designed for the laymen to easily understand.

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Don (Follow me on Industrial Skills Training Blog and on Twitter @IndTraining .)

Saturday, June 26, 2010

Controllogix 5000 Training

Check out this Controllogix 5000 training SlideShare Presentation: and our many others.

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Monday, June 14, 2010

CSI? No … BSI (Breakdown Scene Investigation)

BSI: Breakdown Scene Investigation

It’s not a Crime Scene Investigation (CSI:), but a lot like it. It is a BSI: (Breakdown Scene Investigation), a bit more complicated and technical. Both require control over the scene and the basic scientific investigation technique. Both are often a race against time. The differences being most CSI: shows investigate loss of life, with BSI: loss of production. (Hopefully the machine breakdown this time is just loss of production and money, not actually hurting someone.) The equipment used by the BSI: ‘Agents’ is different too. Usually one or two of the investigators are PLC Techs using a laptop to access the computer that controls machines, called a PLC (Programmable Logic Controller).

First let’s set the BSI: scene above… The girl and guys on far left wearing black BIN PLC Tech hats are holding laptops, the PM Tech lady grabbed a spare PLC module out of the store room, just in case. The mechanic has his tool box. On the far right, is the plant manager who thinks his presence somehow, will speed the repair of the machine? A few operators are standing around as onlookers. Hopefully one of the PLC Techs are questing the operators as witnesses, while breakdown scene is first being secured. The man in the very back could be the production line supervisor.

The cost of all these employees (experts) and the lost production is running at about $10,000 per hour. The clock is ticking, tic-toc!

The maintenance crew has scientific procedures at their disposal too. They don’t just use wrenches, grease guns, volt-ohm meters and laptops. They can chose to use Root Cause Analysis (RCA), Failure Mode and Effect Analysis (FEMA), data analysis tools such as Cpk, SPC, MTBF, PdM, etc. Also they use the most basic and common; non-invasive test, operating and condition monitoring.

The Investigation process:

1. Secure the Breakdown scene.

2. Talk to machine operators (expert witnesses).

3. Take pictures and other data collection. (Maybe actual photographs, but more importantly a copy of the PLC program which preserves the state of all switches, sensors, etc. for later analysis.)

4. Use PLC ladder logic to quickly find machine problem and to minimize downtime.

5. Repair problem, get machine back into production.

6. Perform RCA, PdM etc. for future breakdown prevention.

Don (Follow me on Industrial Skills Training Blog and on Twitter @IndTraining .)