Today, when we inspected the equipment in the workshop, we found that there was a small electronic component connected to the input terminal of a PLC in the electrical cabinet, as shown in the figure below.
I've never seen this happen in my previous job, and it's the first time I've seen it in my more than 10 years as an electrician.
The appearance of this small electronic component is unremarkable, with only two pins sticking out, making it easy to come into contact with the outside world. Out of curiosity, I tried to touch it with my hand, only to be slightly shocked.
Although the shock was not severe, it certainly reminded me of the potential safety hazards posed by this small component. If other operators also accidentally touch it, it can cause more damage.
After taking a closer look at several other PLC modules, I noticed that there were no similar small components mounted on the input terminals. This made me even more confused about the existence of this little component, what exactly does it do? What are the reasons for being installed here?
With these questions in mind, I consulted the relevant technical materials and manuals in the hope of finding answers.
After some hard work, I learned that this small component is actually a resistor for signal conditioning, and its main function is to limit the current of the input signal and protect the input circuit of the PLC module from being damaged by excessive current.
At the same time, it can also play a role in filtering and improving the stability of the input signal.
However, while this small resistor has its justification, the safety hazards it poses cannot be ignored. If the resistance value of the resistor is not selected properly, or the installation position is not reasonable, it may lead to the operator accidentally touching it and causing injury. In addition, if the quality of the resistor itself is unreliable, it can also cause other electrical faults.
Through this unexpected discovery, I realized that in the field of industrial automation, even seemingly small details can hide important functions and potential safety hazards.
In addition, I would like to ask everyone, can this resistor be removed, and will it have any impact?
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