# How to Audit Existing Systems Before Modernizing Industrial Operations
Industrial modernization represents a critical inflection point for manufacturing facilities worldwide. As factories grapple with aging infrastructure originally designed decades ago, the imperative to modernize intensifies with each passing quarter. Yet rushing into modernization without thoroughly understanding your current systems is akin to renovating a building without first inspecting its foundation—potentially catastrophic and almost certainly costly. The audit phase isn’t merely a procedural formality; it’s the strategic cornerstone that determines whether your modernization investment delivers transformational value or becomes an expensive lesson in what not to do.
Before you even consider implementing new technologies, you need to establish a comprehensive picture of your existing operational landscape. This means examining everything from legacy programmable logic controllers to distributed control systems, from network architecture to cybersecurity vulnerabilities. The complexity of industrial environments—where systems often span multiple generations of technology and vendors—makes this assessment particularly challenging. How can you confidently plan a modernization roadmap when you’re uncertain about what you’re actually modernizing?
Pre-audit planning: establishing scope and assessment criteria for legacy industrial infrastructure
Effective auditing begins well before your team sets foot on the production floor. The pre-audit planning phase establishes the parameters, methodologies, and success criteria that will guide the entire assessment process. Without this foundational work, audits frequently devolve into unfocused information-gathering exercises that consume resources without delivering actionable intelligence. Your planning phase should define precisely which systems fall within scope, what data you’ll collect, and how you’ll measure the current state against future requirements.
A comprehensive pre-audit plan addresses several fundamental questions: Which production lines or facilities require assessment? What level of detail is necessary for decision-making? Who holds institutional knowledge about undocumented system modifications? What access restrictions or safety protocols will constrain the audit process? These questions might seem straightforward, but in facilities with decades of operational history, the answers often reveal surprising complexity. Production systems that operators believe function independently may share critical dependencies, while supposedly identical production lines may have diverged significantly through years of independent modifications.
Defining critical assets using ISO 55000 asset management framework
The ISO 55000 family of standards provides a structured methodology for identifying and categorizing industrial assets based on their contribution to organizational objectives. Rather than attempting to audit everything simultaneously—an approach guaranteed to overwhelm even well-resourced teams—the asset management framework helps you prioritize based on criticality, risk, and strategic importance. This framework distinguishes between assets that directly impact production output, those that provide supporting functions, and redundant or non-critical systems that may be candidates for decommissioning rather than modernization.
Implementing this framework requires collaboration between operations, maintenance, and engineering teams to develop a criticality matrix. High-criticality assets typically include bottleneck equipment, systems without backup capacity, and processes that directly affect product quality or safety. Medium-criticality assets might encompass redundant systems or those with available workarounds, while low-criticality assets represent equipment that can fail without immediate operational impact. This classification directly informs audit depth—high-criticality assets warrant comprehensive technical assessments, while lower-priority systems may require only basic documentation review.
Mapping operational technology (OT) networks and SCADA system dependencies
Industrial networks often resemble archaeological sites, with successive layers of technology added over decades without comprehensive documentation. Mapping these networks reveals not only the current architecture but also hidden dependencies that could derail modernization efforts. Your mapping exercise should document every connection between SCADA systems, PLCs, field devices, and upstream business systems. This includes both active data paths and backup or failover connections that may activate only during specific operational scenarios.
Network mapping frequently uncovers surprising realities: production systems that supposedly operate independently may share database connections, remote access pathways, or monitoring infrastructure. Critical control loops may depend on aging servers that no one realized were still in service. Documentation from original installations rarely reflects the current state, as decades of troubleshooting and optimization have introduced numerous undocumented changes. Creating an accurate network topology diagram forms the foundation for subsequent cybersecurity assessments and migration planning, as it reveals which systems can be modernized independently and which require coordinated upgrades.
Assembling Cross-Functional audit teams with process engineers and automation specialists
Successful industrial audits require perspectives from multiple disciplines
Successful industrial audits require perspectives from multiple disciplines because no single role sees the entire lifecycle of an automated system. Operators understand how equipment behaves in the real world, maintenance teams see recurring faults, process engineers know the tolerances, and automation specialists understand the control logic and vendor ecosystems. When you formalize a cross-functional audit team, you move from anecdotal evidence to a structured, 360-degree view of your existing systems.
Start by assigning clear roles: a project owner to coordinate the audit, process engineers to document production flows, control engineers or integrators to review PLC and DCS logic, and IT/OT security specialists to map network and cybersecurity risks. Whenever possible, include at least one experienced operator from each critical line; they often know where “temporary fixes” have become permanent. This multi-disciplinary team can challenge assumptions, validate findings from different angles, and reduce the risk of blind spots that later undermine your modernization strategy.
Establishing baseline KPIs: OEE, MTBF, and MTTR metrics documentation
Without hard numbers, it’s impossible to demonstrate whether modernization improved your industrial operations or merely shifted costs. Establishing baseline KPIs—especially Overall Equipment Effectiveness (OEE), Mean Time Between Failures (MTBF), and Mean Time To Repair (MTTR)—turns your audit into a measurable benchmark. These metrics help you quantify the real impact of legacy systems on uptime, throughput, and maintenance efficiency, rather than relying on subjective impressions that “the line is unreliable” or “this PLC is slow.”
Begin by standardizing how you measure and collect these KPIs across all audited assets. For OEE, define consistent rules for availability, performance, and quality losses, and ensure that shift leaders and maintenance teams agree on how events are classified. For MTBF and MTTR, extract data from your CMMS, PLC logs, or historian and validate it with maintenance staff to correct obvious gaps or miscodings. When you document these metrics alongside equipment age, vendor, and automation technology, patterns quickly emerge—revealing which systems are prime candidates for modernization and where smaller optimizations could yield disproportionate benefits.
Technical infrastructure assessment: evaluating PLCs, DCS, and industrial control systems
Once the pre-audit planning is complete, the next phase focuses on the technical backbone of your industrial operations: PLCs, DCS platforms, industrial control systems, and the communication protocols that bind them together. This is where you translate anecdotal “this system is old” into a precise understanding of hardware, firmware, and software lifecycles. Think of this assessment as a medical check-up for your automation infrastructure—it reveals which components are healthy, which are at risk, and which require urgent intervention.
A structured technical audit documents vendor families, model numbers, firmware versions, I/O utilization, network connections, and dependencies on engineering tools or obsolete operating systems. It also evaluates maintainability: Do you still have access to programming software? Are licenses valid? Are spare parts and vendor support available? By combining these findings with the criticality analysis from your ISO 55000 asset classification, you can prioritize where to focus modernization investments and where a controlled “run to failure” strategy might still be acceptable.
Auditing programmable logic controllers: Allen-Bradley, siemens S7, and schneider modicon compatibility
PLCs are the workhorses of industrial control, but many facilities run a mix of generations from vendors such as Allen-Bradley (Rockwell Automation), Siemens S7, and Schneider Modicon. During the audit, catalog each controller by family (e.g., ControlLogix, CompactLogix, S7-300, S7-1500, Modicon M340), firmware version, and communication options. Identify which devices are already Ethernet-capable and which still rely on legacy fieldbuses or serial links. This information is key for planning phased upgrades and ensuring protocol compatibility across lines and plants.
Next, assess the availability of programming tools and expertise. Are your engineers still using Windows XP to run legacy RSLogix or Step 7 versions? Do you depend on a single external integrator who understands a 20-year-old Modicon program with no documentation? Evaluate whether vendor migration tools exist (for example, from S7-300 to S7-1500 or from PLC-5 to ControlLogix) and what that implies for code conversion and testing. A thorough PLC audit not only highlights obsolescence risks but also clarifies which controllers can be modernized in place and which require a complete replacement strategy.
Distributed control system health checks: honeywell experion and ABB system 800xa performance analysis
Distributed Control Systems (DCS) like Honeywell Experion and ABB System 800xA often sit at the core of continuous processes in chemicals, oil and gas, and power generation. Because they are so deeply embedded, they’re frequently left untouched for years—until performance degradation or support limitations force action. Your DCS health check should examine controller loading, CPU utilization, network latency, alarm loads, and redundancy status. Are redundant controllers and networks functioning as intended, or have they been bypassed during past troubleshooting?
Evaluate the underlying server infrastructure, operating systems, and database versions that support the DCS. Is the system running on virtualized, supported platforms, or on aging physical servers with unsupported Windows versions? Review vendor lifecycle documentation to determine support status and upcoming end-of-support milestones. Analyze operator station performance, alarm management practices, and historical data retention. These insights help you decide whether a phased upgrade, a platform migration, or a comprehensive DCS modernization is the most cost-effective path.
Legacy protocol evaluation: profibus, modbus RTU, and DeviceNet migration readiness
Many industrial plants still rely on legacy fieldbuses such as Profibus, Modbus RTU, and DeviceNet to connect PLCs, remote I/O, drives, and intelligent field devices. While these protocols have proven robust, they pose challenges for integration with modern Ethernet-based architectures and Industrial IoT platforms. During the audit, map where each protocol is used, which devices depend on it, and what gateways or protocol converters are already in place. Pay attention to mixed topologies where newer Ethernet-based devices coexist with legacy buses through daisy-chained gateways.
Evaluate cable condition, segment length, number of nodes, and diagnostic capabilities. Are you frequently facing intermittent communication faults on Profibus segments? Are DeviceNet networks operating near their maximum node count? Consider how migration to Profinet, EtherNet/IP, or Modbus TCP could simplify network management, improve diagnostics, and support higher data rates. However, recognize that not every legacy bus needs an immediate replacement; the goal is to identify where protocol modernization will unlock better reliability, easier troubleshooting, and readiness for data-driven optimization.
Human-machine interface (HMI) obsolescence assessment and touchscreen technology gaps
Operator interfaces—whether standalone HMIs or DCS operator stations—often lag behind in modernization efforts, even though they directly influence productivity and safety. Your HMI audit should inventory all terminals by vendor, model, firmware or software version, and connection method. Many plants still operate panel PCs or proprietary touchscreen terminals that run on obsolete operating systems or rely on unsupported visualization software. These devices can become single points of failure when spare parts dry up or security vulnerabilities emerge.
Assess usability and consistency as well. Do different lines present completely different screens for similar processes, forcing operators to “re-learn” each station? Are alarming, trend visualization, and diagnostics presented in a way that supports fast decision-making, or do they overload operators with raw data? Identifying gaps in HMI technology and design helps you plan for next-generation interfaces—such as web-based HMIs, thin clients, or mobile-ready visualization—while maintaining continuity for operators during the transition.
Cybersecurity vulnerability analysis for industrial networks and connected equipment
As industrial operations become more connected, cybersecurity can no longer be treated as an afterthought in modernization projects. A compromised PLC or historian doesn’t just threaten data—it can interrupt production, damage equipment, or cause safety incidents. The audit phase is the ideal moment to perform a cybersecurity vulnerability analysis tailored to your industrial control systems. Rather than viewing security as a separate initiative, embed it into your overall assessment so that modernization inherently strengthens your cyber posture.
This analysis should consider not only external threats, but also internal risks such as misconfigured remote access, shared credentials, or engineering laptops that bridge IT and OT networks. Industrial cybersecurity frameworks like IEC 62443 and NIST 800-82 offer structured methodologies, but the goal of the audit is practical: identify the most critical vulnerabilities, quantify their potential impact on operations, and prioritize remediation actions that can be integrated into your modernization roadmap.
IEC 62443 compliance gap analysis for zone and conduit architecture
IEC 62443 promotes the concept of dividing industrial networks into security zones connected by controlled conduits. During the audit, evaluate how closely your current architecture aligns with this model. Do you have clearly defined zones for safety systems, control networks, and corporate IT, or does everything reside on a flat network where any device can “see” any other? Document which systems contain safety-critical logic, which manage production control, and which handle data collection or reporting.
Perform a gap analysis by comparing your current setup with the IEC 62443 recommendations for segmentation, access control, and security levels. Identify areas where high-criticality assets share networks with low-security devices such as operator workstations or third-party vendor laptops. Also review existing policies around user authentication, role-based access, and configuration management. This structured view allows you to integrate zone and conduit improvements into network redesigns, firewall deployments, or DCS upgrades, instead of treating them as bolt-on security projects.
Network segmentation review: IT-OT convergence security risks and DMZ configuration
IT-OT convergence—linking industrial networks with corporate IT systems and cloud services—brings clear benefits for data visibility and optimization, but it also introduces new attack paths. As part of the cybersecurity audit, review how your OT networks are segmented from IT, and whether a properly configured demilitarized zone (DMZ) exists. Are historians, remote access servers, and patch management tools located in a controlled intermediary zone, or do they sit directly on the control network?
Inspect firewalls and routing rules between IT and OT segments. Are there any “temporary” rules that became permanent over time, granting broad access where only specific services should be permitted? Document any direct PLC or HMI exposure to corporate networks or the internet, even if only for testing or remote support. This review often reveals quick wins—such as tightening firewall rules, enforcing VPN-based remote access, or re-homing data exchange systems into a DMZ—that can dramatically reduce risk without disrupting daily operations.
Firmware vulnerability scanning using industrial-specific tools like nozomi networks and claroty
Many vulnerabilities in industrial environments arise from outdated firmware or software on PLCs, switches, firewalls, and embedded devices. Manual tracking is error-prone, especially in plants with hundreds or thousands of assets. Industrial cybersecurity platforms such as Nozomi Networks and Claroty can automatically discover OT assets, identify firmware versions, and flag known vulnerabilities based on vendor advisories or CVE databases. As part of your audit, use these tools—or equivalent solutions—to build an accurate asset inventory and vulnerability list.
However, scanning alone is not enough. You also need a practical patch and upgrade strategy that balances security with operational continuity. For each critical asset, determine whether firmware updates are feasible, what testing is required, and how downtime can be minimized. For devices nearing end-of-life with no available patches, consider compensating controls such as tighter network segmentation or access restrictions. Integrating vulnerability insights into your modernization roadmap ensures that new architectures not only improve performance but also reduce your exposure to cyber threats.
Production process documentation: reverse engineering undocumented manufacturing workflows
Many industrial facilities operate on tribal knowledge—processes that “everyone knows” but few have formally documented. When planning modernization, this undocumented know-how becomes a major risk. Changes to automation, data flows, or user interfaces can unintentionally break subtle workarounds, quality checks, or safety habits that operators have developed over years. That’s why a core element of your audit must be reverse engineering existing manufacturing workflows and documenting them in a structured, accessible format.
Start by shadowing operators, maintenance technicians, and quality inspectors on the shop floor. Map each end-to-end process from raw material receipt to finished product shipment, including manual steps, paper-based records, and informal communication channels. Pay attention to “off the books” activities: Excel files operators maintain on personal computers, handwritten labels, or verbal approvals that never reach the MES or ERP. Capture not only the ideal process, but also how people actually respond to exceptions, minor faults, and product changeovers. This level of detail forms the basis for validating that your modernized systems truly support how work gets done.
Data architecture evaluation: assessing historians, MES, and ERP integration points
Modern industrial operations depend on data as much as on physical assets. Yet in many legacy environments, data flows resemble a patchwork quilt of ad-hoc integrations, manual exports, and point-to-point interfaces. Before you can design a modern architecture for industrial data, you need to understand how information currently moves between SCADA systems, historians, MES, ERP, and external partners. The goal of this audit phase is to map your data landscape: where data originates, how it is transformed, where it is stored, and who relies on it.
This assessment should cover not only technical interfaces, but also data quality, latency, and governance. How often do you encounter conflicting production figures between the historian and the ERP? How many hours per week are spent reconciling reports or manually re-entering data from one system into another? By exposing these inefficiencies and inconsistencies, you create a strong business case for a coherent data architecture that enables real-time monitoring, traceability, and analytics—without relying on fragile integrations that break whenever an upstream system changes.
SCADA historian performance: OSIsoft PI system and GE proficy data quality assessment
Historians such as OSIsoft PI System and GE Proficy serve as the memory of your industrial operations, capturing time-series data from PLCs, DCS, and sensors. During the audit, evaluate both their technical performance and the usefulness of the data they store. Are sampling rates appropriate for the processes monitored, or are you either oversampling and bloating storage or undersampling and missing critical events? Check server utilization, storage capacity, and data compression settings to determine whether the historian is scaling effectively with your plant’s growth.
Data quality is equally important. Analyze tags for gaps, flatlines, or unrealistic values that indicate communication issues or misconfigured inputs. Review naming conventions and metadata—are tags named consistently enough that engineers can easily locate data across sites and systems? Assess how historian data is used today: for compliance reporting, troubleshooting, optimization, or predictive maintenance. These findings will shape your modernization priorities, whether that means upgrading hardware, reorganizing tag structures, or integrating historian data with analytics platforms and cloud services.
Manufacturing execution systems integration: SAP MES and rockwell FactoryTalk connectivity audit
Manufacturing Execution Systems (MES) bridge the gap between the shop floor and enterprise planning. Solutions like SAP MES and Rockwell FactoryTalk rely on accurate, timely data from controllers, historians, and ERP to orchestrate orders, track batches, and enforce quality workflows. As part of your audit, document all integration points between MES and underlying control systems: OPC servers, direct PLC connections, web services, or file-based interfaces. Identify where data is pushed versus pulled, and how often synchronization occurs.
Look for fragile dependencies: custom scripts written years ago by a single engineer, undocumented transformations that adjust timestamps or units, or one-way interfaces that make troubleshooting difficult. Interview production planners and quality managers to understand where MES data fails to reflect reality—such as delays in order confirmation, missing traceability links, or discrepancies between planned and actual production. By cataloging these integration challenges, you can prioritize modernization initiatives that deliver immediate value, such as standardizing interfaces, consolidating middleware, or introducing a unified integration layer.
Industrial IoT readiness: edge computing capabilities and MQTT protocol implementation status
Many modernization initiatives aim to leverage Industrial IoT, advanced analytics, or AI to improve operations. However, the success of these initiatives hinges on reliable data capture at the edge and efficient, scalable communication protocols. During the audit, assess whether your current infrastructure supports edge computing—for example, industrial PCs, smart gateways, or modern PLCs capable of running containerized applications or analytics close to the process. Determine whether these devices already publish data using modern protocols such as MQTT, or whether they rely solely on traditional polling-based architectures.
Also review bandwidth constraints, latency requirements, and the robustness of existing networks. Can your current OT network handle additional data streams without affecting control performance? Are you already using MQTT brokers, or is data still centralized through a single historian or OPC server? Evaluating Industrial IoT readiness helps you identify which lines or plants can serve as early adopters for edge analytics or cloud integration—and where preliminary upgrades to networking, compute, or security are needed before these technologies can be deployed safely.
Cost-benefit analysis and modernisation roadmap development using RACI matrix methodology
An audit only delivers value if its findings translate into a realistic modernization roadmap with clear priorities, budgets, and responsibilities. Once you have documented technical risks, performance gaps, cybersecurity issues, and data architecture limitations, the next step is to quantify costs and benefits. Estimate the financial impact of unplanned downtime, quality losses, and maintenance inefficiencies linked to legacy systems. Compare these figures with the projected investment required for different modernization scenarios—incremental upgrades, strategic replatforming, or full system replacement.
To keep this complex decision-making process manageable, use a structured approach such as a RACI matrix (Responsible, Accountable, Consulted, Informed). For each modernization initiative—upgrading a PLC family, segmenting OT networks, replacing HMIs, or standardizing historian architectures—assign who is responsible for execution, who is accountable for outcomes, who must be consulted (for example, safety or quality), and who needs to be kept informed. This clarifies ownership, reduces decision bottlenecks, and ensures that modernization efforts remain aligned with operational priorities and available resources.
Combining cost-benefit analysis with a RACI-driven roadmap transforms the audit from a static report into a living management tool. As projects progress, you can revisit baseline KPIs like OEE, MTBF, and MTTR to validate that changes deliver the expected improvements. You can also adjust priorities as new risks or opportunities emerge—such as equipment reaching end-of-support, regulatory changes, or strategic shifts toward more flexible, data-driven production. In this way, the initial audit becomes the foundation for a continuous modernization journey, rather than a one-off exercise.