It is unfortunate that most electronic and automation EQUIPMENT once installed and running is never serviced until it fails. Although not well documented, it is a good practice to do some kind of Preventive Maintenance check at least once per year. A good Preventive Maintenance schedule should include:
1. Replacement of batteries once a year, record date when changed.
2. Dust of EQUIPMENT with a anti static cloth or duster be careful not disturb wiring or switches.
3. Check all wiring and ground connections for any loose connections, corrosion etc.
4. Be sure environment is clean free of dust, moisture, dirt, grease, grime. Best if kept in an enclosed cabinet.
a. DUST. If allowed to accumulate on electronic EQUIPMENT traps heat and heat build up over time can cause component failures.
b. MOISTURE of any kind, needs no explanation.
5. Check power supply voltages with a DMM if not within specification adjust or replace.
6. Keep a stock of replacement parts for backup.
7. Check or make backups of the software and programs running in PLCs. Record the dates of programs.
This is a brief list of what could be done in a PM plan. Best to perform PMs during scheduled down time.