What is a "wet contactor"

Dry contacts are when there is no electrical current/voltage and the wet ones are when you have voltage/current.

For a tach , most of the old style would have the wires across the points. There would also be the car electrical system connected to the points. That would make them wet. If (probably never found) there were a seperate set of contacts that opened and closed as a shaft on the engine turned and not connected to the electrical circuit of the car, they would be dry contacts.

While not useful in this case, some contactors/relays/switches will have mercury wetted contacts.

In some cases it can mean mercury wetted contacts, but the term "wetted" is also used to describe when dry contacts carry sufficient current to break through any oxide or contaminants on the contact surfaces.

dry contacts is terminology used to describe contact frovided as part of a device that are ot connected to any internal circuit and singnal by chngeing from insulator to conductor,

by extension wet contacts must be switching current

I'm guessing that this wet/dry terminology is borrowed from hydraulics

In an automobiles before crank position sensors became common the tachometer output would be taken from the ignition coil (where the points or electronic ignition connects). There'd be a programmabile divider to compensate for how many cylinders the engine has.

Once again I have not told the whole story :-(

I was going to use this tach on my milling machine spindle, not my car. I think it works by pulsing a circuit between 2 of its connector pins. It also can be pulsed by " ... PNP or NPN proximity switch, HALL sensor". Does that help determine what the mean by "wet contactor"?

Bob

A french kisser!

it seems that they bsically mean anything that generates a pulse every time the shaft rotates, what sort of sensor do you want to use?

I'd like to use a magnet on the spindle and a reed switch. It's about the most contamination proof. If the reed switch is "wet".

I asked this question of the (Chinese) seller, not expecting any real answer. I was not disappointed: "Really so sorry. I do not know what the problem is. I hope you can understand"

Would you ask this question of the person operating the cash register at Home Depot?

One or two electrical retailers have surprised me - but discount stores are just box shifters.

While there are mercury wetted reeds, it may just be a matter of Chinglish word meanings.

A mercury wetted contact has less "contact bounce" than a dry contact and maybe that was what they were alluding to.... maybe they are really saying the tach is sensitive to bounce on the input?

Getting a hall sensor would be a good idea IMO. They are potted, sealed and hard to destroy, and have no contact bounce.

it means the source for the tach can come from a live pulse source elsewhere instead if using the a reference sournce from the tach unit to a isolated switch. Basically an external source that supplies its own power source to generate an output reference signal

In the terms of Dry contacts, it means that the contacts can not be shared with others reference sources on those termination points and thus the two connections to the contact must be dedicated to the tach unit. this also applies to sensors dedicated to the tach for use.

In the case of Wet contacts as for this subject, it means the tach can use an electrical pulse from other sources and most of the time the input as a wide range scale to allow this.

Picking off an existing inductive sensor that is powered from another circuit is a good example. just combine the commons .

Jamie

I wonder if Nolox can be used to increase current when applied on top of the oxides its supposed to prevent.

Thanks to my repliers.

I decided that using a reed switch would involve too much fabrication & fiddling with a mounting. Instead I bought another tach that had a Hall effect sensor.

wimp!

hall effect sensor: that would probably work as a "wet contactor", I guess it's a bit late now though.

I considered that long enough to find that the prices of the tach-with-sensor and tach plus sensor were the same.