PLC and HMI fault finding

When a machine stops partway through a cycle, repeatedly alarms or waits for a signal that never arrives, the fault needs to be understood within the operating sequence.

PMI investigates problems including:

Machines failing to start or complete an automatic cycle.
PLC inputs changing without the expected machine response.
Outputs failing to operate connected equipment.
HMI communication faults, missing status information and unexpected displayed values.
Recurring alarms following hardware, software or configuration changes.

We trace PLC logic, inputs and outputs, sequence conditions and feedback from connected devices. This connects what the software expects with what the machine is actually doing, helping us identify where operation is breaking down.

EtherCAT, PROFINET and industrial network diagnostics

Industrial networks connect the controllers, drives, remote I/O and devices that a machine depends on. Communication faults can interrupt individual functions or stop the entire production process.

PMI provides specialist fault finding for EtherCAT, PROFINET and other industrial networking and communication systems.

EtherCAT fault finding

We investigate EtherCAT problems including:

Devices failing to reach the Operational state, or remaining in PRE-OP or SAFE-OP.
Working counter errors and interrupted process-data communication.
Missing devices, link faults and intermittent communication losses.
Drive or I/O communication problems following component replacement or configuration changes.

Our investigation brings together device diagnostics, network layout, power, cabling and configuration. We trace the reported fault through the connected equipment to establish where attention is needed.

PROFINET diagnostics

PMI investigates PROFINET communication and configuration problems, including:

I/O devices appearing offline or failing to communicate with the controller.
Device-name and IP-address issues.
Differences between the configured system and the equipment installed.
Communication dropouts involving controllers, drives and remote I/O.
Problems that appear after a device has been replaced or the network changed.

We examine the controller diagnostics, device configuration and physical network together, checking the communication the machine expects against what is actually taking place.

Communication between industrial devices

Our work also covers communication and signal exchange between PLCs, HMIs, drives, remote I/O and connected machinery.

We investigate missing data, inconsistent device status and interrupted signals across the installed system, bringing network knowledge together with an understanding of the machine’s control sequence.

Servo drive and motion-control diagnostics

A drive alarm or positioning fault can involve the controller, motor, feedback system, communications or mechanical load.

PMI investigates motion-control problems including:

Servo drives that will not enable.
Axes failing to home or complete a commanded movement.
Encoder and motor-feedback faults.
Positioning and following errors.
Intermittent movement faults and drive communication problems.

We consider the drive, motor, feedback and machine mechanics as a connected motion system. That approach helps identify whether the work concerns configuration, electrical components, communications or the mechanical conditions affecting the axis.

PLC software changes and machine interfaces

When equipment is added, replaced or removed, the controls and communication between machines need to reflect the new arrangement.

PMI supports modifications to existing PLC programs, parameters and machine interfaces. We work through the required operating sequence, connected devices and signals to establish how the installation needs to function.

For linked machinery, this includes investigating the ready, start, enable and completion signals exchanged between systems. A machine waiting for another machine’s response needs the communication and sequence examined together.

Changes are planned around the existing control software, I/O, device configuration and production requirements, with the intended operation and checks agreed before work begins.

Expertise in Beckhoff, Rexroth, Inovance and CODESYS systems

Our industrial automation experience includes:

Beckhoff and TwinCAT — PLC and machine-control systems, EtherCAT communications and fault finding.
Bosch Rexroth and IndraDrive — Drive and motion-control investigations, with experience using IndraWorks and DriveTop.
Inovance equipment — Automation, drive and motor applications.
CODESYS-based systems — PLC control environments and machine software.

This controls expertise is backed by practical CNC and machinery fault-finding experience. We understand how the software, electrical equipment and mechanical process interact in a working machine.

Automation components, replacements and upgrades

When a fault requires a replacement component, PMI combines automation component sourcing with the engineering knowledge needed to assess its suitability.

We consider the installed controller, drive, motor, feedback, communications and configuration when evaluating a replacement.

For ageing systems, we can investigate obsolete automation parts and replacement options. Where a CNC machine needs a wider change, a control upgrade or retrofit assessment can help establish the practical route forward.

Industrial automation FAQs

Why can the PLC be running while the machine will not complete its cycle?

A running PLC can still be waiting for an input, drive status, position confirmation or response from another machine. PMI traces the sequence conditions and connected-device signals to identify what is preventing the next step.

Why is an EtherCAT device staying in SAFE-OP?

If the device is expected to enter Operational but remains in SAFE-OP, its diagnostic information and the master’s configuration need investigation. Process-data settings, device status and the conditions required for the transition help guide the checks.

PMI examines the device within the EtherCAT system to establish why normal operation has not been reached.

Why is a PROFINET device offline after replacement?

The replacement needs the correct device identity and configuration for the installed system. Device naming, addressing, expected modules and network connections are relevant checks.

PMI investigates the replacement setup and controller diagnostics to establish what is preventing communication.

Speak to PMI about your automation requirement

Bring specialist controls, motion and industrial networking expertise to your next machine fault or automation change.

Send the details you have, including:

The machine or process and the problem you need to solve.
Exact alarms, fault codes or a description of the required change.
Controller, HMI, drive, motor and network-device details, where relevant.
Your site location, production impact and required timing.

From our Craigavon base, we provide engineering coverage across Northern Ireland and the Republic of Ireland.

Discuss your automation requirement Get help with an automation fault

Email pmi-enquiries@precisionmachineindustries.com with equipment photographs, fault-screen images and relevant documentation.