Trying to understand the meaning of "dry contact closure".

I am trying to detect if a small low power fan (like the ones in a computer) is on or off. Can the I/O Linc sensor input be used for that ?

No.  At least not directly w/o putting some kind of sensor on the fan/circuit.

Dry contact closure basically means an open or short circuit like that provided with a relay.

It is also possible to use an electronic circuit (like a transistor or optoisolator) to simulate a relay contract closure.

20 minutes ago, gzahar said:

No.  At least not directly w/o putting some kind of sensor on the fan/circuit.

Dry contact closure basically means an open or short circuit like that provided with a relay.

It is also possible to use an electronic circuit (like a transistor or optoisolator) to simulate a relay contract closure.

Do you have any details on how to "convert" the current on the fan circuit into a dry contact circuit which could be used with I/O Linc?

49 minutes ago, drinkwater said:

Do you have any details on how to "convert" the current on the fan circuit into a dry contact circuit which could be used with I/O Linc?

using a relay with the same coil voltage that the fan operates on.  the contacts of the relay are 'dry contacts"

28 minutes ago, MrBill said:

using a relay with the same coil voltage that the fan operates on.  the contacts of the relay are 'dry contacts"

A cheap automotive 12VDC relay may pull in at 5VDC.  Some experimentation may be required.  You'll want to look at the "Coil Pull In Voltage" in the specs before purchasing.

Sorry, I was thinking about detecting if the fan died, not whether it was turned on/off.

@MrBill's suggestion should work fine.

Otherwise, you might be able to use something like this (for 12V fans) as a front end to the relay:

https://www.amazon.com/Temperature-Control-Speed-Controller-Module/dp/B019P0FLHW

(Using a relay instead of the buzzer)

22 minutes ago, PhanTomiZ said:

A cheap automotive 12VDC relay may pull in at 5VDC.  Some experimentation may be required.  You'll want to look at the "Coil Pull In Voltage" in the specs before purchasing.

if the fan is 5V why wouldn't you just order the appropriate 5v Relay?

It's a 24v fan. Not sure why it says DC24v - the fan is used in a circuit board which is powered by 240v AC.

 

2 minutes ago, drinkwater said:

It's a 24v fan. Not sure why it says DC24v - the fan is used in a circuit board which is powered by 240v AC.

https://www.amazon.com/HiLetgo-Channel-Module-Isolation-Support/dp/B00LW2H5GC/

Do you want to know if the fan has power or if the fan is turning?  It looks like there is a tachometer terminal on the fan you are showing. No wire attached.

7 minutes ago, tmorse305 said:

Do you want to know if the fan has power or if the fan is turning?  It looks like there is a tachometer terminal on the fan you are showing. No wire attached.

I just need to know if their is power to the fan - to be able to convert that into a dry contact for the I/O Linc sensor input.

11 minutes ago, MrBill said:

https://www.amazon.com/HiLetgo-Channel-Module-Isolation-Support/dp/B00LW2H5GC/

How would I wire that up with the existing wires on the fan (sorry if I asking too much) ?

3 minutes ago, drinkwater said:

How would I wire that up with the existing wires on the fan (sorry if I asking too much) ?

Depends on how good you are with a soldering iron.  I would tack on two more wires right there at the fan where you see the red and black wires attach.

Probably the simplest way is to use some type of wire tap like this: https://www.amazon.com/Nicelux-Electrical-Connectors-Connection-Self-Stripping/dp/B07ZC4CTLW

which crimps on.

1 minute ago, MrBill said:

Depends on how good you are with a soldering iron.  I would tack on two more wires right there at the fan where you see the red and black wires attach.

Probably the simplest way is to use some type of wire tap like this: https://www.amazon.com/Nicelux-Electrical-Connectors-Connection-Self-Stripping/dp/B07ZC4CTLW

which crimps on.

I think I can solder it on the existing fan wires. Was thinking more about how to connect to the relay you mentioned and then from their to the I/O Linc input sensor.

Red to DC+ and IN.  Black to DC-.  (there is a jumper on that model that needs to be set to high position).

C and NO go to I/O link sensor input (ground & sense).

2 minutes ago, gzahar said:

Red to DC+ and IN.  Black to DC-.  (there is a jumper on that model that needs to be set to high position).

C and NO go to I/O link sensor input (ground & sense).

Cool! Thx a million to everyone for all your help.