The Best Five Minutes You Can Spend: PLC Health Check

Step 1 — Check CPU Diagnostics for Early Warnings

Your PLC already logs how it’s performing — you just need to look.

Here’s what to do:

1. 1. 1. Open your controller’s diagnostic or event log.
         • Every system keeps one — whether it’s built into the PLC software, displayed on an HMI, or accessible through your SCADA dashboard.
      2. Review warning messages, not just faults.
         • Warnings often flag communication hiccups, I/O delays, or scan-time variations.
         • Make note of any messages that repeat or occur at the same time each day or shift.
      3. Check CPU load, memory utilization, and cycle time
         • A gradual increase in load or cycle time— or too many interrupts —can indicate that logic changes, tag growth, or background processes are stressing the controller.
         • Capture a quick screenshot for future comparison
      4. Confirm your diagnostic log retention.
         • If messages are rolling off too quickly, increase storage depth or export the log periodically.
         • Keeping a short weekly record helps establish a performance baseline.

Why it matters:

Diagnostics aren’t just post-failure data — they’re your early-warning radar. Catching recurring errors early prevents alarms and unexpected shutdowns.

Step 2 — Look for “Bad” or Stale Tags in SCADA

Your control system is only as reliable as its data. A few bad or stale tags often hint at deeper communication or device issues — easy to spot with a quick scan.

Here’s what to do:

1. 1. 1. Open your tag or data-quality summary.
         • Most SCADA or HMI systems include a view that shows tag status, quality, or update rate.
         • If you don’t have a dedicated report, start simple — look for internal features or status bits that confirm the data is valid, even when the value doesn’t change.
      2. Check for missing or frozen data points.
         • Note any values that haven’t been updated recently—they often point to communication drops or outdated tag references.
         • If possible, set up a basic tag or logic “health check” to flag inputs that aren’t updating as expected.
      3. Review network or device communication logs.
         • See if “Bad” tags line up with brief network interruptions, device restarts, or scheduled maintenance windows.
         • Save these logs to spot recurring issues over time.
      4. Clean up or document persistent bad tags.
         • If a tag is obsolete or intentionally unused, label it clearly or remove it from active screens to reduce alarm noise.
         • If it should be active, trace it back to the PLC address or I/O channel and verify it’s mapped correctly.

Why it matters:

Bad or stale tags quietly erode trust in your data. Left unchecked, they hide real process issues, create false alarms, and distract operators from what really matters. Addressing these “focus thieves” keeps your SCADA data dependable and your team alert.

Step 3 — Review Alarm Activity and Flood Counts

When alarms stack up, clarity disappears. A quick review separates real issues from noise.

Here’s what to do:

1. 1. 1. Open your alarm summary or event log.
         • Sort or filter by frequency to see which alarms appear most often.
         • If possible, check how many alarms were active or acknowledged in the past 24 hours or during the last shift.
         • Pro tip: If your system allows, schedule an automatic export of alarm logs to a secure folder. Reviewing changes over time reveals trends before they escalate.
      2. Identify recurring alarms or patterns.
         • Watch for the same tag, device, or time of day repeating.
         • Repeating alarms usually mean a process setpoint, sensor, or communication link needs attention.
      3. Check for alarm floods or bursts.
         • Look for time periods where hundreds of alarms triggered at once — often during startup, power recovery, or batch transitions.
         • Make note of which events triggered the spike.
      4. Acknowledge and categorize.
         • Separate nuisance alarms (which fire too easily) from critical alarms (which truly require response).
         • Adjust alarm priorities or categories to make root causes clearer and reduce operator fatigue.

Why it matters:

Alarm floods overwhelm your HMI and wear down awareness. Reducing nuisance alarms and spotting patterns strengthens reliability and keeps real issues from getting lost in the noise.

Step 4 — Make Sure Your System Tells Time the Same Way

Your system doesn’t need perfect time to run — but you need consistent time to make sense of events when something goes wrong.  Even minor time mismatches can complicate troubleshooting across systems.

Here’s what to do:

1. 1. 1. Confirm all devices share a common time source.
         • Whether your system uses a plant network server, GPS receiver, or IT-managed NTP service, make sure PLCs, HMIs, historians, and servers all reference the same clock.
      2. Compare timestamps for a known event.
         • Check the same event — like a pump start, alarm, or batch phase change — across multiple systems. If the timestamps don’t align, your synchronization needs attention.
      3. Check synchronization status or drift indicators.
         • Most control systems log time-sync status or offset. If you see warnings or deviations, resync the device or verify that your master clock source is accessible.
      4. Record your time source setup.
         • Document which device or service provides your master time and how often other devices sync to it. This makes future troubleshooting faster and audits easier.

Why it matters:

In troubleshooting, timing matters as much as events. Synchronized clocks keep alarms, trends, and logs aligned so you can find answers quickly and avoid time-drift confusion.

For more on why time synchronization supports effective event logging and alarm management, see ANSI/ISA-18.2-2016 and NIST SP 800-82 Rev 3.

Step 5 — Confirm the Date of Your Last Full Backup

A control system is only as safe as its last backup. Configurations change and updates roll out, but backups often get forgotten until they’re needed most.

Here’s what to do:

1. 1. 1. Locate your most recent full project or configuration backup.
         • Check your engineering workstation, network drive, or backup server.
         • Verify that the backup includes current logic, HMI screens, and configuration files — not just a partial export.
      2. Check the date.
         • If it’s older than a month (or your plant’s maintenance cycle), make a new one now.
         • Use consistent file naming and versioning so you can easily identify the latest revision.
      3. Confirm accessibility.
         • Try opening the backup or validating the archive. A corrupted or password-locked file is as bad as no backup at all.
      4. Store safely and redundantly.

• • • • Keep at least one copy offline or in a controlled location, separate from the primary network.
      • Maintain milestone backups for key stages like commissioning or major updates, and label each version clearly. Once stable, reduce backup frequency per plant policy.
      • Once the system has run stably for several months with no changes, routine backups can be less frequent, depending on plant policy.

Why it matters:

The best backup is the one you can use. A recent, verified copy turns disaster into downtime avoided — protecting logic, schedules, and peace of mind.

Keep the Habit, Build the Reliability

If you already do some of these checks, you’re ahead of the curve — this list helps make them a consistent habit that builds reliability and confidence in your control system.

If your quick review uncovers deeper questions — recurring faults, performance drift, or aging hardware — Pigler Automation can help. Our engineers work with plants every day to assess control-system health, strengthen reliability, and plan the next right steps for long-term performance.