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AC current detection?

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I am working on some high powered stuff, which is cooled by a fan. Aside from some thermal interlocks, I would like to monitor and control the fan's operation. The fan's already there which uses 110V AC line. Is there anything that would give me an optically isolated simple signal? I don't care if I get an analog or digital signal, but I want it to be optically isolated. Thanks!
 

I guess the easiest way is to use a opto-isolator, this has a LED inside its package coupled to a phototransistor. You will need to add an external diode to protect the LED against reverse voltages and feed it via a 100K resistor from the 110V line. The transistor can then be connected into some other circuit with a typical isolation up to 3KV - depending on your PCB layout!
Frank
 

If all you want to do is monitor current flow through the fan, you could insert a small resistor in series with the fan and use the voltage drop across the resistor to drive the LED input side of an optoisolator IC. Instead of the resistor, you could have three diodes in series and another three in reverse parallel to the first three. Neither of these two will tell you if the fan is locked. The resistor or diodes could also be at the output of a bridge rectifier with the fan in series on the input side of the rectifier.

If it's mechanically convenient, you can have the blades rotating in a photo-interrupter path. Or Use a reflective type of interrupter on one side.
 

There is Hall-effect current sensor ICs manufactured by leading compines, which gives you good isolation.

google for the "Hall-effect current sensor ICs "
 

Thanks for all the replies. This hall effect sensor is exactly what I need. Simple and good isolation.

nandhu015 said:
There is Hall-effect current sensor ICs manufactured by leading compines, which gives you good isolation.

google for the "Hall-effect current sensor ICs "
Click to expand...
 

The professional way is to sense the airflow in case of a filter getting blocked. The most reliable way is to use a diaphram type pressure switch rather then a vane operating on a micro switch, these always fail due to the arm and vane wobbling about in the airflow and breaking off.
Frank
 

Taking a different approach: assuming you fan has opaque blades, why not use an IR LED on one side and an IR sensor on the other so each time a blade passes it interrupts the light beam. This works in my system and it's easy to measure the exact rotational speed as well.

Brian.
 

That would be a great approach if I can get access to the blades. Sorry I didn't make that clear.

betwixt said:
Taking a different approach: assuming you fan has opaque blades, why not use an IR LED on one side and an IR sensor on the other so each time a blade passes it interrupts the light beam. This works in my system and it's easy to measure the exact rotational speed as well.

Brian.
Click to expand...
 

simple and perfect way is use ct transformer it's a best


 

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