Do you have an up to date list of all PLC model types, part availability, program copies and details for your company?

The first step to take is to perform a PLC audit. Open every electrical panel, and write down the PLC brand, model, and other pertinent information. Then go the next two steps. Analyze the audit information and risk, then act on that analysis. To help you out, I want to share with you our company PLC audit form.


Collected Information

Recommended Action

Machine or Area Name

Ex: warehouse conveyor, pump station 3,Strapper 2, Line 7, Traffic signal west main, etc.

PLC Program Name

Ex: 1789GAA1, P3, Strap2, 5872443, WestMainTL, etc.

Network Node Address

No two addresses will be the same. Ex: 2, 3, 17, 21

Network Name

Common to be same as Program name, but not mandatory.

PLC Brand

Ex: Allen Bradley, Siemens, Schneider, Mitsubishi, DirectSoft, Omron

PLC Model Number

Ex: PLC-5/25, SLC-504, SIMATIC S5, MELSEC FX1N, DL 405

Is Spare Available

Yes on shelf, or only in less critical machines or no

Date Program Last Backed Up

Make program backups part of your semiannual PM program

Discriptored Copy of program available

Without discriptored copy of program, troubleshooting and downtime are greatly increased.

Does PLC have EEPROM

Or other method of storing backup program in a chip on PLC

Last date Program Changed

Remember to log when outside consultants or OEM make  program changes too.

Last date EEPROM Burned

Should be saved to EEPROM (Burned) after every successful program change.

Date battery last changed

See manufacturer’s data for recommended change frequency.

Other information you may need

Might be facility location when corporate HQ is using this form.


Once you have collected the basic information in your Plant wide and/or corporate audit, you need to analyze the information to develop an action plan based on risk analysis. In the risk analysis, bottlenecks and other factors will help you assess priorities. Starting with the highest priority PLC, you will need to ask more important questions.

  • Do we have the most common spares for the PLC?
  • Is the OEM (Original Equipment Manufacturer) available 24/7? Or even in business any more?
  • Do we have a back up copy of the PLC program?
  • Does our program copy have descriptions so we can work with it reliably and efficiently?
  • Do we have the software needed to view the PLC program? Are our maintenance personnel trained on that PLC brand?

These are some of the questions our managers must ask, to avoid unnecessary risk and to insure reliability.