Automation failures are rarely caused by a simple fault. Increasingly, they are the result of degraded signal integrity and increasing electromagnetic interference. The increasing complexity of systems and data transfer rates have led to the emergence of a new silent enemy: degraded signal integrity and increasing electromagnetic interference (EMI). This noise, generated by inverters, switched-mode power supplies, and contactors, affects everything from the precision of drives to the stability of communication between PLCs and HMI panels. This results in sporadic but difficult-to-diagnose errors that disappear as quickly as they appear, leading to frustration and unplanned downtime. To effectively combat this invisible threat, technicians must equip themselves with tools that allow them to visualize these phenomena. In this article, we will present the essential techniques and measurement equipment that are key to the stability of a modern, digital plant.
Power quality measurement and interference sources
Many problems with unstable automation and digital signal interference stem from the power supply . If the power supplied to the control cabinet is not stable and clean, no amount of advanced filtering and shielding will guarantee reliability.
Power quality analyzer
The most important tool for assessing the health of a network is a power quality analyzer . This device allows technicians to see what's really happening with the voltage by measuring not only its RMS value but also transient events.
It is essential because it allows the measurement of:
-
Dips and Swells - Momentary, sharp voltage changes that can reset controllers or damage sensitive power supplies.
-
Waveform distortion is the main hidden problem. Devices such as inverters and modern power supplies distort the ideal sine wave from the mains and introduce high-frequency noise into the installation . This noise spreads throughout the installation and attacks low-voltage communication lines, such as those in Profinet networks. This distortion is responsible for sporadic, random communication errors that are difficult to pinpoint.
These measurements are used to verify compliance with standards such as EN 50160 , which defines acceptable voltage quality. In the context of plant-generated noise, it is crucial to verify compliance with IEEE 519 , which regulates acceptable levels of harmonic distortion.
The analyzer allows you to quickly pinpoint problematic power supplies, filters, or drives that introduce the most noise into the control cabinet. This allows you to take specific technical actions.
Digital signal diagnostics
Verifying the physical condition of communication signals is an important aspect of modern maintenance diagnostics. It's not enough to know that a message isn't being delivered; you also need to understand why . A digital oscilloscope is used for this purpose .
An oscilloscope is essential for observing signal waveforms in the time domain . It provides insight into the actual quality of the signal transmitted over Profibus, Profinet, or EtherCAT networks. Without it, a technician only sees a communication error. With an oscilloscope, they can see the cause of the error.
When diagnosing industrial networks, an oscilloscope is used to verify the signal's shape and voltage level in the time domain. Deformation indicates a damaged filter or grounding problem. Measuring the presence of reflections is crucial . If the cable is too long, damaged, or has improper termination (terminal resistance), the signal bounces off the end of the line. This is visible on an oscilloscope as ringing , or jitter. Signal reflections falsify data and cause sporadic communication errors. By measuring the rise and fall times of the edges , you can determine whether the cable or communication port is overloaded or damaged.
It's worth remembering that a protocol analyzer decodes data packets and checks whether they are logically correct. An oscilloscope, on the other hand, verifies the physical layer of the transmission, meaning whether the electrical impulse carrying the data is healthy and clean. Without a clean physical signal, no protocol will function properly.
EMI interference location
While an oscilloscope is essential for verifying signal quality over time, it's not ideal for locating sources of electromagnetic interference (EMI) in the air or within enclosures. This requires a different perspective.
Spectrum and frequency analyzer
A spectrum analyzer, unlike an oscilloscope, measures the signal in the frequency domain . This allows technicians to see the specific frequencies at which noise occurs in the control cabinet and how intense it is. This allows them to identify the specific component. Noise generated by a faulty switching power supply will have a different frequency distribution than noise generated by a motor.
Near-field probe and EMC standards
The most precise tool for locating electromagnetic leaks is near-field probes . These are small loop or electrical probes that, when combined with a spectrum analyzer, allow for the precise location of the leak at the PCB, cable harness, or cabinet screen level. This allows the technician to avoid having to replace all the components and precisely eliminate the source of the interference, for example, through improved grounding or shielding.
These measurements are also referenced in IEC/EN 61000 standards . If the module is operating unstable in an environment that generates interference, you can verify that the level of that interference does not exceed the standards for which the device was designed.
In today's automation landscape, relying solely on mechanical fault knowledge and simple fault diagnosis is insufficient. Electrical noise, waveform distortion, and signal integrity issues pose an increasing challenge.
Mastering noise and signal measurement techniques using a power quality analyzer , oscilloscope , and spectrum analyzer is currently the highest level of maintenance diagnostics. The right equipment in the hands of an experienced technician can turn sporadic and random errors into predictable and remediable problems. The ability to see invisible interference contributes to the stability and long-term reliability of modern industrial automation.
