What are the common causes and effects of sensor and actuator failures in PLC systems? (2024)

All electronics regardless of their nature or application fail from one thing; heat. The source or cause of the heat is the root cause. It may have come from dithering or the constant minor fluctuations of an output to the device. Or perhaps a snubber needs to be added for a pressure sensor, maybe the sensor is the wrong application? Years ago I had a job where the actuators wouldn't last 3 months on a triple stage heat exchanger system used in a high pressure steam plant. After several false starts I was contracted to be the fix. We rotated the actuators 90° so the heat wouldn't transfer up into the actuator and that seemed to solve the problem.

The most common sensor failures are due to physical damage - someone bumped into it, a card bumped into it, etc.Sensors can fail due to a variety of issues - 1. Mechanical sensors wear out with time - they need to be inspected and replaced as they near end-life. 2. Sensors are subject to the environment - they get dust, oil, glue, printer ink, product, and other substances on them that lower their life expectancy. 3. The failure points of every sensor are different; some will fail at the connector, others have poor moisture insulation, others won't work if dust or residue builds up, etc. The key to avoiding all of those is to understand the application and the maintenance cycles and to assign a competent person to audit the system.

At the very beginning of my career in industrial automation I was an electronic engineer used to machine installation and testing and I saw several sensor failures mainly based of poor installation or failure in applying correct guidelines. Sometimes I found misconnection issues due to a failure to read the installation manual! Most of the problems happened by hardware installation.

Numerous factors contribute to sensor and actuator failures, some of which can be mitigated through sound design principles, careful product selection, and a robust installation strategy. Traditionally, all sensors and actuators were hardwired to a PLC/DCS system, introducing an additional point of failure that could render the sensor or actuator inoperative or trigger device failures.

There are many other types of sensors that are significantly more common than those listed. Primarily; photo optic and proximity sensors. These sensors are used for detecting presence or absence of parts or cartons (or other objects). As well as for detecting the position of tooling or other objects being controlled by an actuator or conveyor (etc.). There are 3 main types of photo optic sensors; diffuse reflective (this includes laser), retro-reflective, and through beam. Each has its own defined purpose and use as well as price point. Failure modes for these sensors is almost identical to the physical sensors mentioned earlier. Operational failure is usually due to having the wrong sensor for the job.

I advocate for technologies like Profibus DP/PA and similar fieldbus solutions. These solutions optimize the interface between sensors and actuators and higher-level control systems. Although they are wired, they offer advantages in terms of installation simplicity and fault diagnostics. Leveraging fiber optic cables and media converters, a robust fieldbus installation can be planned efficiently without exceeding project budgets, promising a favorable return on investment. The ultimate goal is to make the sensor and actuator interface infrastructure highly reliable, almost impervious to issues.

La eficaz solucion de fallas relacionadas con sensores y actuadores en sistema de control electrico/ electronico industrial empieza por una detallada descripcion e identificacion de tales equipos en la documentacion del proyecto, en segundo lugar esta el identificar los posibles modos de falla del sistema cuando tal o cual dispositivo falla ademas agregar alarmas descriptivas para cada modo de falla donde se identifique el dispositivo y su lugar en el dibujo esquematico de control y en tercer lugar pero no menos importante es la capacidad de los tecnicos e ingenieros encargados de solucionar la falla para poder evaluar de manera logica /metodica los sintomas de una falla y determinar la mejor manera de solucionarla / mitigarla / by-pasearla

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⚡As I do in my work with windturbines, to prevent sensor and actuator failures in PLC systems, adopt a proactive maintenance strategy 🛠️. Choose sensors/actuators compatible with your PLC, considering factors like accuracy and power. Regular calibration and testing are crucial to ensure they meet tolerance levels. Also, frequent cleaning and proper lubrication help eliminate interference from dust or moisture. #PLCMaintenance #IndustrialAutomation #OT

It is imperative to thoroughly comprehend the specific requirements for each sensor and actuator, taking into account factors such as the installation environment—whether it's indoors or outdoors, the prevailing weather conditions, high-temperature or high-vibration zones, intrinsically safe or chemically charged zones, and microclimates influenced by the processes and products involved. A comprehensive understanding of these criteria, coupled with extensive product knowledge, is crucial for making informed selections.

Sensores redundantes En sistemas que trabajan 24/7 el depender de un solo sensor para continuar con los procesos es muy riesgoso , por esto es recomendable el tener más de 1 sensor en diferentes posiciones monitoreando lo mismo para detectar o dejar de detectar cambios de estado en el proceso.

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Some thing important for actuators is zero position. For a system that protect by a valve, this is important that what happend after auto shutdown or trip. Some times we need to check orifice size of HYD actuators.

Moreover, installation expertise is paramount to ensuring a successful integration. In many instances, exceptional product choices have been marred by subpar installations. To avoid such pitfalls, diligent attention must be devoted to installation techniques, combining best practices, original equipment manufacturer (OEM) recommendations, and practical experience. The contemporary trend leans towards digitization, which has reached the sensor and actuator level through technologies like ASI and IO LINK. These platforms effectively address many of the traditional wiring challenges but demand strict adherence to their respective guidelines for ensuring high availability and longevity