How to distinguish between the contact types of travel switches
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I would like to ask all the forum members: do Pneumatics’ proximity limit switches have dry contacts or wet contacts? How can you tell, and what is the method for making such a determination?
Wet contact point, operating voltage, wiring with positive and negative poles
I originally thought it was a dry contact as well, but it didn’t seem right; however, I didn’t have any professional explanation for it.
How can one tell if there is a fate connection or not? It seems that the wiring doesn’t distinguish between positive and negative poles; it was because of this lack of distinction that I thought it was a dry contact, but now I think that’s not correct.
You should mention the voltage levels first so that it’s easier to make a judgment; for the second voltage level, there will definitely be both power supply function and output function, as clearly indicated in the diagram
Sorry, my wording was incorrect; I didn’t read the instructions. There is voltage drop and leakage current – it’s an electronic switch
The output current is indicated there; how could it still be a dry contact? But we need to check again whether it meets the intrinsically safe standard.
Haha, if the travel switch sends a digital signal, then it must be dry contacts. Ask me why I know it – it’s a 2-wire system, right? Two wires are needed to supply power, right? There are no batteries installed on the travel switch, so there’s no power source; the power must come from the DCS side, right? So what else could that travel switch be? It must be a dry contact. If you ask this question, first of all the person who posed it needs to understand that dry contacts also carry electricity when in use; the difference between dry and wet contacts lies merely in where the power supply is located. No matter what kind of signal it is, it’s impossible to measure it without electricity. If the power is supplied from the DCS side, then the limit switch on site will have dry contacts; if the power is supplied from the limit switch side (in which case two additional wires are required to supply power to the limit switch itself), then the limit switch on site can have wet contacts. Additionally, it is recommended that the original poster search on Baidu for the differences between dry contact signals and NUMAR signals; these are the two most common types of differences in travel switch signals.
To determine whether it is a dry contact (passive) or a wet contact (active), look from the signal output side inward: if there is no power supply inside, it is a dry contact (passive); if there is a power supply inside, it is a wet contact (active). This is true for contact signals, and it is the same for analog signals as well. Regarding the aforementioned determination principle, this proximity switch outputs a dry-contact (passive) switch signal. The operating current ranges from 2 to 100 mA; this is the current that can flow through the switch during normal operation, and it is not the output current.