Author: Justin Snoke
A machine control system is a lot like your car. If you want it to remain reliable, safe, and predictable, it requires routine inspection and maintenance, not just reactive repairs when something fails. Skip oil changes long enough and even the best engine will seize. Ignore the warning signs in a control system, and you risk unplanned downtime, safety exposure, and costly emergency upgrades.
A structured control system health check is the equivalent of a comprehensive mechanical inspection. It identifies risks early, prioritizes corrective action, and creates a roadmap that prevents catastrophic failure.
Below are the top five early warning signs that your control system needs a Controls Systems Health Check.
The top five early warning signs that your control system needs a Controls Systems Health Check.
1. Spare Parts Are Becoming Difficult to Obtain
Every control system has a life cycle. The PLC, HMI, drives, I/O modules, and networking hardware that were once state-of-the-art will eventually become mature, then obsolete.
Most major manufacturers follow a lifecycle pattern:
- Active lifecycle: ~10 years of full production and support
- Mature/limited support phase: 10–20 additional years with reduced availability
- Obsolescence/discontinuation: Parts become special-order, refurbished-only, or unavailable
Once a system moves beyond 20 years, replacement parts for critical components can become extremely difficult to source. It often starts innocently, searching secondary markets like surplus suppliers or eBay. Eventually, even those channels dry up.
At that point, every critical component becomes a ticking time bomb:
- A failed PLC CPU may mean days or weeks of downtime.
- An obsolete HMI may require a full software conversion.
- A discontinued drive may require mechanical and electrical rework to replace.
The Controls Systems Health Check will:
- Inventory all critical components (PLCs, HMIs, drives, I/O, network hardware).
- Identify manufacturer lifecycle status.
- Classify risk based on spare availability and lead times.
- Evaluate existing on-site spare strategy.
- Recommend phased migration or upgrade paths.
Instead of reacting to failure, you gain visibility into how exposed your operation truly is and how much time you have to act.
2. Operators Struggle to Use the System (and Let You Know About It)
If operators regularly complain about a machine, that feedback should not be dismissed as routine grumbling. Operator frustration is often a symptom of deeper control system issues.
Common warning signs include:
- “This machine is the hardest one to start.”
- “You have to know the trick to get it to run.”
- “The alarms don’t make sense.”
- “We just bypass that part.”
As systems age, several things tend to happen:
- HMI screens no longer reflect current operating practices.
- Documentation is lost or outdated.
- Tribal knowledge replaces formal procedures.
- Logic modifications are made without updating operator interfaces.
- Startup and recovery sequences become unnecessarily complicated.
Poor usability directly impacts uptime, training time, and safety. A system that is difficult to operate is also more likely to be operated incorrectly.
A health check addresses this by:
- Interviewing operators, maintenance, and engineering personnel.
- Observing actual startup, changeover, and fault recovery procedures.
- Reviewing HMI design against modern best practices.
- Identifying gaps between control logic and operator interface.
- Recommending practical improvements.
Often, meaningful improvements do not require a full control system replacement. Targeted HMI redesign, alarm cleanup, sequence clarification, or improved documentation can significantly reduce frustration and increase productivity.
When operators trust and understand the system, performance improves across the board.
3. The Control System Has Increased Alarms, Especially Nuisance Alarms
An increase in alarms—particularly nuisance or repeat alarms—is a strong indicator that a control system needs attention. Operators should rely on alarms as meaningful indicators of abnormal conditions. When alarms become frequent, repetitive, or insignificant, they lose credibility. The result is alarm fatigue, slower response times, and increased operational risk.
Common Types of Nuisance Alarms
- Chattering alarms (rapid cycling due to poorly tuned setpoints or missing deadbands)
- Stale or standing alarms that remain active for long periods
- Duplicate alarms triggered by the same root cause
- Improperly prioritized alarms (non-critical events configured as high priority)
- Alarms active during normal states such as startup or maintenance
Over time, process changes, instrumentation drift, and undocumented logic modifications degrade alarm performance. In some cases, alarms were never rationalized in the first place.
Per ISA-18.2 alarm management principles, alarms should be actionable and require a defined operator response. If operators routinely ignore or disable alarms, the system is no longer functioning as intended.
The Control Systems Health Check will:
- Analyze alarm history and frequency trends.
- Identify recurring “bad actor” alarms.
- Evaluate priority distribution.
- Review deadbands, delays, and suppression logic.
- Compare alarm configuration to operating procedures.
- Assess alignment with ISA-18.2 lifecycle best practices.
The outcome is an alarm rationalization roadmap that restores clarity, improves situational awareness, and ensures true abnormal conditions stand out when they matter most.
4. The Safety of the Machine Makes You Nervous
If the safety of a machine makes you uneasy—because of unclear safeguarding, bypassed interlocks, or undocumented safety logic changes—that concern should not be ignored.
Under ISO 12100, machine safety begins with a formal risk assessment process:
- Identify hazards.
- Estimate and evaluate risk.
- Apply risk reduction using the hierarchy:
- Inherently safe design
- Safeguarding and protective measures
- Information for use
If the original risk assessment is outdated, or if machine modifications were made without revisiting it, the actual risk profile may no longer match the documented one.
Warning Signs of Safety Erosion
- Light curtains or interlocks frequently bypassed or muted
- Tooling or speed changes without safeguarding validation
- Safety PLC logic modified without documentation
- No clear Performance Level (PL) or Safety Integrity Level (SIL) determination
- Obsolete safety components
- Panels no longer aligned with NFPA 79 or UL 508A practices
Standards such as ISO 13849-1, IEC 62061, and IEC 61508 require that safety-related control systems achieve and maintain validated risk reduction levels. If PL or SIL calculations cannot be produced, or if architectural assumptions (redundancy, diagnostic coverage, fault tolerance) are no longer valid, the integrity of the safety function is questionable.
The Control Systems Health Check will:
- Confirm a risk assessment has been completed and review per ISO 12100.
- Verifying safeguarding implementation.
- Confirm necessary safety functions identified in risk assessment exist.
- Confirming existing PL/SIL calculations and architecture.
- Inspecting wiring and panel practices against NFPA 79 and UL 508A.
- Reviewing management of change (MOC) history.
Safety degradation is often gradual. A structured review restores documented assurance and ensures the machine meets current expectations, not just past ones.
5. You’re Ready to Enter the Modern Age with Networking and Data Collection
Real-time data, remote visibility, OEE tracking, and predictive maintenance are becoming standard operational expectations. Many legacy systems, however, were never designed for enterprise connectivity.
Common limitations include:
- PLCs without Ethernet capability
- Proprietary or unsupported communication protocols
- HMIs with no secure remote access support
- Flat network architectures with no segmentation
Attempting to “bolt on” connectivity without planning introduces cybersecurity risk. Per ISA/IEC 62443, modernization efforts should implement defined security zones, conduits, and defense-in-depth strategies, not direct connections between legacy controllers and business networks.
The Control Systems Health Check will provide a structured path forward by:
- Documenting current physical and logical network architecture.
- Identifying communication capabilities and limitations.
- Evaluating cybersecurity posture (unsupported OS, open ports, default credentials).
- Assessing upgrade options (communication cards, gateways, edge devices).
- Recommending modernization aligned with ISA-95 integration models.
Modernization does not always require a complete rip-and-replace. Strategic additions, such as secure edge gateways, protocol converters, or segmented VLAN architectures, can bridge legacy systems into modern data environments while preserving operational stability.
Final Thought
Control systems rarely fail without warning. The signs are usually there—obsolete hardware, frustrated operators, alarm overload, creeping safety risk, or pressure to modernize.
A control system health check converts those warning signs into actionable insight. It replaces uncertainty with documented risk, prioritized recommendations, and a practical path forward.
Just like routine vehicle maintenance prevents a seized engine, a structured Control Systems Health Check prevents costly downtime, safety incidents, and emergency upgrades.