What are the most challenging PLC hardware problems that you have faced or solved?

another major reason for power supply fluctuations is not enough ventilation jn the cabinet for heat dissipation when they are placed too close to vfds

Power supply issues in control systems are fairly straightforward to diagnose. The problems arise with intermittent failures that are often due to poor incoming line voltage levels, harmonics, high resistance due to corrosion, etc. You'd need a good multimeter and, in rare instances, an oscilloscope to diagnose those types of problems. Backup or redundant power supplies are an option, but the failure rates of power supplies are so low that they're rarely recommended.

1.Ground Integrity Ground integrity also serves as a sound barrier that protects against electrical white noise. 2.Electrical Noise Interference The most common cause of electrical noise is electromagnetic interference, which typically occurs when a large motor is activated or when lightning hits nearby. Another cause of electrical noise is radio frequency interference. 3.Heat (operating environment ) One of the biggest dangers for electronic components is excess heat. A PLC system surrounded by heat-emitting equipment could be at risk of failure if not properly safeguarded. As a general rule, all equipment should be maintained at T&H Otherwise, the PLC and/or peripheral part could overheat and fail to work properly.

Some of the toughest problems with PLC hardware include intermittent faults, where issues pop up irregularly, making them hard to catch. Power supply problems can mess up the whole system, but it's tough to figure out if the issue is with the power supply unit itself or something else. When input or output modules fail, it can throw everything off, and finding the faulty module without causing more trouble is tricky. Communication problems are another headache, especially when PLCs need to talk to other devices or systems. Overheating in tough environments or due to poor cooling can also cause problems. Improper grounding or electrical noise can interfere with signals, causing malfunctions.

I endose other professionals's response, I will 3 possible reasons: 1) Variations in the power supply voltage or current can disrupt the delicate electronics within a PLC, leading to malfunctions. These fluctuations can be caused by factors like power grid instability, brownouts, or surges. Also because of UPS malfunctioning. 2) Using a longer cable from the UPS to power supplies can indirectly impact, like DeltaV Bulk Powers are recommended to use with surge suppressors. 3) Extreme temperatures, dust, humidity can or improper panel design (heat dissipation issues) all contribute to the early degradation of a power supply's components. This can shorten its lifespan and increase the risk of unexpected failures.

When replace faulty main plc CPU (slave) with new, observe steady REDF on both Master-Slave and continuous blinking BUS2F is coming.

I/O Modules are the most frequent to fail in control systems. In most instances, they'll fail due to load troubles - Ex: moisture, mechanical failures / stickiness, electrical shorts, etc. If the input failed, do the following: 1. Activate the field device to check the light on the input module. 2. Check if the associated tag is functional in the PLC. 3. If the tag works, there's no issue with that input. If the light doesn't come on, there's an issue with the input or the field device. Measure voltages to eliminate one or the other. On the output side, the easiest way to check for failure is to actuate the output via the PLC. Check the voltage level at the output card to eliminate the output block as the culprit.

Las fallas de módulos I/O en especial los remotos vía Ethernet pueden fallar por diversas causas pero una vez me tocó enfrentar un problema de falla general del módulo y al ser un sistema Rockwell donde los módulos se integraban como parte del DLR, la falla fue debido a que IT agregó un servidor y puso de manera equivocaba la misma dirección IP del módulo de I/O y causó una falla general de todo el módulo, esto es poco probable que suceda pero fue mi experiencia y lo identifiqué al sacar el módulo de servicio y verificar si había IP duplicada y allí me di cuenta que había un servidor instalado ese mismo día con la misma IP, es por ellos que Módulos remotos I/O deben estar segmentados y ser parte de una VLAN diferente a la de HMIs.

Right, I agree, most common I/O module failure: Loose wiring, causing intermittent signal drops (e.g., sensor signal not consistently reaching the PLC). But you know what, operation team surprisingly will blame on PLC Programming for any fault.

Facing SF and SB faults on a Siemens S7-400 PLC with multiple nodes, including ET200, proved challenging. Initially, attempts to trace and replace the node connector didn't resolve the issue. Thorough checks on resistors and proper documentation were conducted, but the problem persisted. It was only after a meticulous inspection of the shielding on the connectors that the problem was finally identified and resolved. This experience underscores the importance of considering shielding integrity in troubleshooting, showcasing how addressing this aspect can have a significant impact on resolving complex faults in a multi-node Siemens PLC setup

Establishing a successful communication between PLC and third party devices is the challenging part in the communication network. I experienced it as more challenging when existing PLC or devices are upgraded to new system. These problems depending on the communication protocol, No. of devices connected to the PLC, Distance between PLC and the devices etc. To minimize these challenges, PLC system integrator should have knowledge on 1) communication protocol that is used. 2) Network interface (Ethernet, serial etc..) and configuration parameters. 3) PLC programming. 4) basic knowledge on the connected devices. 5) Exp. in trouble shooting. Finally we have to make sure that customers can really rely on it and avoid manual tasks.

Depending on the network, these problems range from simple to fairly complex to figure out. Most modern networks / hardware provides an interface that will immediately tell the technician / engineer where the problem is at a bare minimum. With older networks (ex: ControlNet, DeviceNet) you're not going to get away so easily... There's benefit in understanding how to understand the software diagnostics, and which hardware components are needed to narrow down the problem (ex: end of line resistances). It's also important to know how to map the data for those network in case you need to make changes or troubleshoot signals on remote modules.

if devices are connected to work in a device level ring, majority of the times people forget to configure DLR supervisor and topology using DLR tool leading to communication failures

Well, long distances impact data transfer speed especially in case of serial communication. Secondly, EMI affects communication and data corruption not because of you but because of proejct team who used same cable tray or trench. Then I want to highlight my experience that radio (walkie-talkie) also affects HMI communication if you are using some adaptors at workstation. These things need to be reconsidered and fixed.

Communication protocols are one of the challenging tasks in PLC . A single wrong parameter can lead to no communication . In old protocols even diagnostics were not available. Bringing security can leads to more complexity and they tangle the engineers. Configuration of OPC DA in domain vs workgroup over network Adding end terminating resistance or configuring DLR network... Susceptible to interference..or calculation of Electrical load in Foundation Fieldbus to daisy chaining communication, not configuring properly Process image producer consumer assembly , Connectors , Resistors,Cable all play an important role in having proper communication. If configured properly it work like charm otherwise can give nightmare.

The service life of PLC load memory is mainly affected by the no of write/delete cycles, so if you’re going to enable data logging in it, you need to check the calculation provided by the manufacturer to calculate its deterioration and change before corruption.

Bueno más que desafiante, fue el más raro.. Una vez integré un PLC S7-1200 a un S7-300 que tenia una CPU antigua, por lo que me fijé cual rango de direcciones de I/O estaban disponibles para la transferencia de datos (como es lo lógico). Entonces veo que se usaban los rangos de la 0 al byte 50, en adelante estaba sin uno, hasta que llego al byte 100 y volvía a estar ocupado. Definí entonces que trabajaría en el byte 51 hasta el 90 (Como estaba sin uso no debería haber problemas). Sin embargo no había transferencia de datos, era raro porque todas las otras configuraciones estaban bien, la capa física ok, pero no había comunicación. Al final se reemplazó la CPU antigua por una nueva, se cargó el HW y sin problemas...

Memory and Processor Problem: Insufficient memory or processing capability can lead to program execution errors or slow performance. Solution: Monitor memory usage and program size. Optimize PLC programs to reduce memory footprint. Consider upgrading PLC hardware if performance limitations are consistently reached.

External Devices Problem: Compatibility issues or failures with external devices (e.g., sensors, actuators) connected to PLCs. Solution: Ensure that external devices are compatible with PLC specifications and communication protocols. Test devices individually to isolate compatibility issues. Use appropriate signal conditioning or isolation techniques if needed.

The external devices like Glue, and Glue piston were connected with the PlC controller using Profibus and the variable assigned for this on the HMI part should be checked correctly and the connections with the devices and controllers should be made properly.

Intermittent issues due to environmental factors are incredibly difficult to diagnose and troubleshoot. I've been in a few scenarios in which intermittent issues were reported; needless to say, there was no way to reproduce the incident and most of the logs weren't adequate to understand where the problem originated. The only way to protect against "weird" signal levels that may occur due to humidity, corrosion, dust / debris, etc, is to create systems that log the errors and memory bits - you can go over this information after the issue has manifested itself and understand what the root cause was.

You might have the most robust PLC with redundancy but improper or lack of grounding can drive your PLC haywire. Encountered these problems in a newly commissioned plant during lightnings strike: 1. Some analog parameters produce spikes causing plant shutdown. Temporary remedy was to put the affected parameters in manual mode during lightnings strike. Later on, the problem was traced to mixed dirty and clean grounding. 2. RTU PLC I/O channels getting fried. Realized that due to lack of grounding for field instruments, lightning surge travel to PLC panel. Adding local ground rod connected to field instrument housing solved the problem.

Agree with Mr Welson. We also faced plant shutdown due to poor grounding on AI signal failures connected with PCS7 based ESD system.

I was at a chemical production facility where one particular type of I/O card was failing in large quantities, but all other control system components performed without issue. The failures started after a quality testing lab was moved to a room adjacent to the equipment. After many tests of power feeds and loads and inspection of signal wiring, it was finally theorized that vapors from chemicals used in the lab were reacting with the circuitry or solder of the 4-20 mA analog input cards, which apparently had different metallurgy than other components, even from the same manufacturer. The theory was never proven but all failures stopped when a more powerful vent hood was installed above the chemical storage area in the adjacent lab.

Environmental Factors Problem: Harsh environmental conditions (e.g., temperature extremes, humidity, dust) can impact PLC hardware reliability. Solution: Implement protective measures such as enclosures, climate control systems, or environmental monitoring to mitigate adverse effects of environmental factors on PLC equipment.

Special care is needed when performing arc welding on skid-mounted package units where PLC cabinet is located on the same skid. I encountered such an issue while working on a skid-mounted NG compression unit. During arc welding, a high amperage current flows from the welding electrode to the grounding lug. It is essential to clamp the grounding lug as close to the welding electrode as possible. If the distance b/w two electrodes increases during welding, the current will follow the shortest available path, given that the entire skid is grounded. This poses a risk to field instrumentation or PLC cabinet installed on the skid, exposing them to high amperage current which could result in partial or permanent damage to the electronic equip.

Analogue modules always failing as most of the maintenance do not connect shields back when replacing sensors or cross connect them.

Additional Considerations: Regular Maintenance: Implement a proactive maintenance schedule to prevent hardware failures and address issues before they escalate. Documentation and Support: Maintain thorough documentation of PLC hardware configurations, wiring diagrams, and troubleshooting procedures. Utilize manufacturer support resources and online communities for guidance on challenging hardware problems.