Replacing a Faulty Analog Input Card in a PLC Rack in Continuous Process Industries: Step by Step Procedure

For continuous process industries, replacing a malfunctioning analog input card in a PLC rack is a crucial task that must be carefully planned and carried out to prevent plant operations interruptions. In order to securely replace and configure a new analog input card, check all settings, and ensure smooth operation, this article provides a thorough, step-by-step process.

In continuous process industries, analog input cards in PLC racks are essential for reading real-time data from field instruments such as transmitters and sensors. Faulty analog input cards can lead to inaccurate readings or complete loss of signal, compromising process control and safety. 

This procedure covers the detailed steps for safely replacing a faulty analog input card, ensuring proper configuration, and verifying signal data to avoid operational issues.

Step 1:Safety Measures

During this procedure, it is of the highest priority to make certain that both individuals and equipment are safe. Be sure to adhere to following safety guidelines:

Personal Protective Equipment (PPE)

• Wear PPE such as gloves, eye protection, and an anti-static wrist strap to prevent accidental discharge that may damage the new card.
• Antistatic Precautions: Proper grounding is crucial when handling sensitive electronic equipment.

Click here for Role of Anti-Static Wrist Straps in Industrial Automation

Hazard Assessment for Replacement Procedure

1. Assess potential hazards related to equipment, confined spaces, electrical exposure, and environmental factors.
2. Review and comply with relevant method statements, Job Safety Procedures (JSP), and area-specific safety guidelines.
3. Develop a Job Safety Analysis (JSA) outlining each task step, associated hazards, and mitigation measures. Include Lockout/Tagout (LOTO) and PPE requirements to control risks.
4. Ensure area is clear of non-essential personnel, and verify equipment status before starting replacement.
5. Clearly define the scope of the replacement procedure, identifying all components involved.
6. Check historical data or incident reports in similar environments to understand common risks.
7. Involve experienced personnel (operators, maintenance teams) in the assessment to gather insights on potential hazards.
8. Identify risks of electric shock, arc flashes, or exposed conductors if working with powered components.

Emergency Preparedness

• Ensure that emergency protocols are in place and accessible to all personnel involved.
• Confirm that any emergency shutdown (ESD) procedures are ready to implement if required.

Step 2:Stoppage Planning for Analog Input Card Replacement

Assess Operational Impact:

• Evaluate how the replacement will impact plant processes, considering any dependent systems or critical functions.

Replacement Scenarios: Scheduled Stoppage:

• If a live replacement is not feasible, arrange a planned stoppage by coordinating with operations and production teams.
• Inform all affected departments about the scheduled downtime and work with the scheduling team to select a time with minimal production impact.
• Confirm availability of all required tools, replacement parts, safety documentation, and procedural guidelines.
• Test backup equipment if available, and ensure all replacement steps are in place to keep downtime as short as possible.

Replacement Scenarios: Live Replacement:

• For AI cards part of a redundant system, confirm redundancy with the automation and control teams to allow live replacement without disrupting operations.
• Review the redundancy failover procedures and provide the team with a briefing on backup plans in case of unexpected issues.

Documentation and Approvals:

• Ensure that all necessary work permits, risk assessments, and approvals from relevant departments are completed ahead of time for both scenarios.

Step 3:Specification and Firmware Verification for Analog Input Card Replacement

Compatibility Confirmation:

• Ensure the replacement analog input card is fully compatible with the existing system configuration to avoid communication issues and ensure proper functionality.

Specification Check:

• Model Number: Confirm that the model number of the replacement card matches the faulty card.
• Input Range, Resolution, and Signal Type: Verify the input range (e.g., 4-20mA, 0-10V), resolution (e.g., 12-bit, 16-bit), and signal type align with system requirements.

Environmental & Electrical Requirements:

• Confirm that the replacement card meets the plant’s environmental standards, including voltage and temperature tolerance.
• Ensure compliance with the system’s electrical specifications (e.g., power requirements, insulation, noise immunity).

Firmware Version Check:

• Current Firmware Verification: Confirm the firmware version on the replacement card and verify compatibility with the PLC or control system software.
• If an update is necessary, follow the manufacturer’s guidelines to upgrade the firmware on the replacement card.
• Ensure the firmware upgrade process includes any required configuration steps to support seamless communication and functionality.

Analog Input Card key Components Overview – Example 

This guide provides a detailed description of the main components on an analog input card, referencing an example below image for clarity. Each part is essential to the card’s functionality and secure integration within the ControlLogix system. 

1. Backplane Connector: Serves as the primary interface connecting the module to the ControlLogix system backplane, enabling communication with other modules.
2. Top and Bottom Guides: Ensure accurate alignment by guiding the Removable Terminal Block (RTB) or Interface Module (IFM) cable onto the module.
3. Status Indicators: Display the status of module communication, health, and input/output devices, providing visual feedback crucial for troubleshooting.
4. Connector Pins: Enable input/output, power, and grounding connections to the module via the RTB or IFM, facilitating signal transfer from field devices.
5. Locking Tab: Secures the RTB or IFM cable to the module, helping maintain stable wiring connections.
6. Keying Slots: Designed to mechanically key the RTB, these slots prevent incorrect wiring connections by ensuring only compatible connectors align with the module.

Click here for Understanding PLC Racks and Chassis: Types, Differences, and Purposes

Step 4:Replacement Procedure for Analog Input Card

Locate Faulty Card:

• Use the PLC’s diagnostic tools or consult alarm logs to identify the faulty analog input card.
• Confirm the malfunction by cross-checking system diagnostics and reviewing any error codes or warning indicators.

Grounding and Anti-Static Precautions:

• Wear a properly grounded anti-static wrist strap to prevent electrostatic discharge (ESD) damage.
• Avoid touching the card’s connectors or sensitive areas to reduce the risk of ESD damage.

Remove Faulty Card:

• Always consult the manufacturer’s manual for specific instructions on unlocking and removing the card, as procedures can vary.
• Follow the manual’s guidance to release any retention clips, latches, or screws holding the card in place.
• Carefully slide the faulty card out of the slot, avoiding any force that could damage the backplane connectors.

Insert New Card:

• Consult the manual for instructions on inserting and securing the new card, ensuring proper alignment and compatibility with the system.
• Align the new card carefully with the slot to prevent misalignment or connector damage.
• Once in place, secure the card using the retention clips, latches, or screws as specified in the manual.
• Verify that the new card is detected by the PLC system.
• Need to Conduct a brief functionality check  to confirm proper installation and operation of the new card.

How do you check analog input in PLC?

Step 5:Installation and Configuration of New Analog Input Card

Parameter Configuration:

• Channel Settings: Within the PLC software, configure each channel’s with at least following parameters.
• Input Range: Set the input range (e.g., 4-20mA, 0-10V) as per the system requirements.
• Scaling: Define scaling to convert input signals accurately into process variables.
• Filter Settings: Adjust filtering parameters if necessary to stabilize signal readings.

• Channel Assignment: Assign each channel to its respective field instrument or transmitter within the PLC programming software.
• Input Scaling: Apply input scaling for each channel, if required, to ensure signal accuracy.

HART Protocol Configuration (if applicable):

• For channels using HART, enable HART communication in the configuration software.
• Verify that the new card communicates correctly with HART-enabled field devices, ensuring diagnostics and additional parameters are read as expected.
• Set up any required HART-specific parameters, like polling addresses or response time settings.

Click here for Common Causes of Programmable Logic Controller(PLC) Failure and Mitigation Strategies

Verification of Signal Data:

• Use a signal generator to apply standard input values (e.g., 4mA, 20mA) to each channel, checking that readings match expected values.
• Cross-verify the input values on the PLC software with those displayed on the local display or HMI to confirm accuracy.
• For HART-enabled channels, verify that HART data such as diagnostics and secondary variables are correctly received by the PLC.
• Ensure no communication faults are present between the PLC and HART field instruments.

Click here for more PLC articles.

Calibration and Normalization:

• Channel Calibration: Use standard signals (e.g., 4-20mA or 0-10V) to calibrate each channel, aligning readings with actual process values.
• Signal Address Verification: Confirm that each channel’s signal address is correctly mapped in the PLC software.
• Document calibration settings and signal addresses for each channel for future reference.
• Perform a system-wide check to ensure all channels are operational, configured correctly, and communicating effectively with their respective field devices.
• Review any configuration changes for consistency and completeness, and secure settings within the PLC software.

Click here for Programmable Logic Controller (PLC) Program Backup Checklist

Step 6:Normalizing the LOTO Procedure and Powering 

• Carefully remove all Lockout/Tagout (LOTO) devices (locks and tags) applied during the isolation process, following your facility’s LOTO procedure.
• Ensure each lock and tag is removed by the personnel who applied them or by authorized individuals, as required by safety protocols.
• Re-energize the PLC rack or module to restore power to the system.
• Verify that the newly installed analog input card powers on correctly and that there are no errors or warnings on the PLC.
• Inform all relevant personnel, including operations, maintenance, and control teams, that the LOTO procedure has been normalized and that the system is now operational.
• Confirm with team members that the replacement has been successfully completed, and the system is ready for normal use.

Click here for Getting Started with PLC Hardware and Software

Step 7:Completion and Documentation for Analog Input Card Replacement

Recordkeeping:

• Document the serial number, model, and firmware version of the newly installed analog input card.
• Record all configuration settings, including input range, scaling, filter settings, HART parameters (if applicable), and any other key parameters configured during installation.
• Note the reason for replacement (e.g., malfunction, upgrade), any calibration data gathered during installation, and adjustments made to match actual process values.
• Document any relevant modifications in the system that could impact operations or future maintenance.

Critical Spares and Procurement:

• Review the inventory levels of critical spare parts and determine if additional analog input cards should be procured to maintain readiness for future replacements.
• If a service contract or warranty exists with the card’s manufacturer, record the replacement details for tracking purposes. Include dates, installation information, and related documentation to streamline warranty claims if needed.

Completion Confirmation:

• Attach the documentation to the asset management system, maintenance logs, or any relevant database.
• Ensure all documentation is accessible for future reference and troubleshooting, and notify relevant teams that the replacement process has been completed.

Step 7:Post-Replacement Testing

Signal Validation

• Compare each analog input’s reading in the PLC software with the displayed values on the local HMI or DCS. Ensure all signals are accurate and reflect the true values from the field transmitters.
• Confirm that critical analog signals (e.g., pressure, temperature) match expected values from field instruments. If discrepancies arise, investigate and recalibrate as necessary.

Operational Verification

• Observe plant operations for any unusual behavior or anomalies following the card replacement.
• Respond promptly to any alarms or discrepancies in signal readings. 
• Analyze and resolve any issues that may be due to incorrect configuration or connection errors.

Testing While Plant Running

• For replacements done live, observe real-time values and trends on the HMI or SCADA system to ensure continuous, accurate signal processing.
• Confirm that each analog input signal on the PLC or SCADA matches the field data, ensuring that no drift or inconsistencies are present.

Click here for Root Cause Analysis of PLC Remote I/O Panel (Point I/O Panel) Cards Failure Issues.

Faulty Analog Input Card Replacement Checklist in PLC Rack- Downloadable

Replacing a faulty analog input card in continuous process industries requires careful planning and execution to ensure uninterrupted operations. 

This detailed checklist guides technicians through each step, from safety precautions to post-replacement testing, to ensure a smooth and safe replacement. Refer the below link to download the checklist in excel format.

Click here for more Essential Instrumentation activities Checklists