In an ideal world, every failure would look the same: a loud crack, the machine stops, and a clear message appears on the screen indicating the damaged component. Although a complete production line shutdown is painful and costly, from the perspective of a maintenance engineer, it is a stable and logical situation. They know what happened, replace the damaged component, and the device returns to work, or an external service is engaged. However, situations where the machine stops without apparent reason and then restarts after a moment, as if nothing happened, are problematic. Transient faults are random and harder to detect phenomena that generate a cascade of further problems. It turns out that for business stability and human safety, a capricious machine is much worse than one that has definitively refused to obey.
Does a green light on the controller always mean safety?
It might seem that a failure is simply a downtime, but in the context of safety systems, the difference between a permanent and a transient fault is fundamental. A complete failure of a Safety element, such as a light curtain or a interlock switch, usually puts the machine into a safe state. Production stops, but people are safe. Transient faults are much more insidious in this respect and can lead to life-threatening situations. If the disturbance lasts less than the safety controller's scan cycle, it may not be caught by self-diagnostic systems.
Such an error lulls security into a false sense of security. Imagine a loose contact or corroded connection in an E-STOP button circuit. If the circuit breaks for only a fraction of a second due to vibration, the machine may make an uncontrolled movement or fail to stop in time before the controller can even react with an error. This would be a dangerous and undetected situation.
How undetected analog errors destroy a production batch?
Another aspect is the degradation of production quality. A complete failure has the advantage of stopping the process, and defective parts simply are not produced. A sporadic error allows the machine to work but introduces disturbances into the process that are not visible at first glance.
This particularly applies to analog circuits. A transient error, such as a momentary jump in temperature or pressure reading caused, for example, by EMI disturbances, can cause the PLC controller's algorithm to oversteer the process. There may be momentary overheating of the material or insufficient clamping of the element. Since the signal quickly returns to normal, the machine does not report an error and continues to work. Such a situation can last for hours or even days, generating production waste. Often, only the quality control department realizes that the process is unstable, and material losses in such a scenario often exceed the costs of a simple repair.
Why do operators lose trust in machines?
This struggle also has a destructive impact on the human factor. The prolonged occurrence of unexplained errors leads to a gradual loss of trust in technology. When the machine stops randomly, and the cause cannot be located, operators stop taking error messages seriously. They begin to ignore alarms or reset them reflexively without any verification, treating every signal as another false alarm. This is a straightforward path to a serious mechanical failure or accident when that one real warning signal is ignored. Equally difficult is the situation of maintenance technicians who work under pressure to report, which undermines their competence in the eyes of management.
Where do transient faults come from?
To effectively combat this phenomenon, it must be understood that transient faults do not come from nowhere. Their causes are usually purely physical, though subtle and often related to the aging process of the installation.
One of the main culprits is micro-corrosion of contacts. Machine micro-vibrations cause minimal movements at the connections, leading to surface oxidation and transient interruptions in conductivity, which may disappear after wiggling the cable.
Another source is electromagnetic interference, where invisible waves induce voltages in poorly shielded wires, falsifying signals only when large drives are switched on nearby.
Cold solder joints, i.e., cracks in the solder on printed circuit boards that open the circuit only at high temperatures and conduct current again after the cabinet cools down, are also a common problem.
In summary, the difference between a complete failure and a transient fault is the difference in the scale of the challenge. A complete failure is a technical problem, so the specialist knows what to replace, does it, and forgets about it. A transient fault is a systemic problem, affecting budget, safety, and work psychology. It requires a completely different approach, advanced diagnostic tools, and expert knowledge that allows subtle symptoms to be combined into a logical whole.
That is why it is worth focusing on prevention. A professional audit of the machine park, including verification of wiring condition, thermovision of control cabinets, or analysis of power quality, is the most effective insurance policy for your production. It allows for detecting and eliminating potential sources of disturbances before they turn into costly and difficult-to-diagnose downtimes.
