Where can I find an inexpensive one?
I don't need any precision, just the confirmation that a fan is actually spinning and that the duct it is in is not obstructed.
Where can I find an inexpensive one?
I don't need any precision, just the confirmation that a fan is actually spinning and that the duct it is in is not obstructed.
*Anything* which is ATEX approved is going to be expensive. You may be unlucky in your search. JB
JB:
Clearly I meant "APEX inexpensive". $500 would be great, $100 incredible.
What _type_ of fan? There clearly are PC fans available with a built-in sensor. Even this old box of mine says CPU fan is at
2100RPM, chassis fan at 2280. ...Jim Thompson-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
Jim Thompson:
About 2 feet diameter, used, with other two, to ventilate a 100 ft. underground passage in case of gas leakage.
Maybe something as simple as a Hall sensor to detect the fan blade going by?
But detecting air flow itself can get tricky. ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
Jim Thompson:
The problem is that ATEX thing, otherwise even a simple piece of plastic with two strain gauges tacked on could work.
Another interesting idea would be to use something like this:
I was also thinking about looking in the power supply and see if the moving motor distorts the sine wave when moving.
It would be a plus, so we could also know that the duct is not obsructed by a dead rat. But a big one indeed.
this:
two self heated NTCs in a bridge, on shielded from the airflow, one in the airflow.
a differential air pressure sensor, freescale has some with hose connections so the electronics doesn't have to be in or near the duct
-Lasse
Put a thermistor in a housing so it reduces self-generated convection. Connect it to a circuit which both provides enough current to self-heat the thermistor and read the voltage across it. If you use a PTC thermistor,then it has a sharp break at a specific temperature. The fan cools the thermistor, and if the airflow drops below some threshold, the resistance rises and it can shut off the equipment, cause an alarm, or whatever. (Mainframe) computers had these in the 1960's, so it is OLD technology.
Jon
I have some of these kicking around somewhere. IIRC they were made by TI. If you request I'll go looking and see if I can come up with the part number for you. Art
Read my 1962 MIT thesis... except I was measuring blood flow ;-) ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
snipped-for-privacy@fonz.dk:
The problem is that, if some connection breaks (or the NTCs get damaged) the current circulating would cause a spark, and you don't want that in an ATEX environment.
Better, much better.
Only problem is the fact that, wit an obstructed duct, the pressure is going to rise a lot, unless the obstruction is such that the fan stalls and the pressure drops again.
It should still work because it's differential. Think pitot tube. A swinging vane and a microswitch is a low tech solution that almost anyone could diagnose and fix a problem with. Art
Artemus:
Except for the spark that they always do when opening.
The fundamental problem is that anything with an Ex marking must go through a very expensive approval and is generally used in very expensive (high energy = lotsa money) and rare places. So the high approval costs must be divided among few units, which therefore cost a lot even when trivial and/or "intrinsically cheap".
snipped-for-privacy@fonz.dk:
The more I think about it, the more it seems a good idea. Tomorrow I will see where the "Ex area" ends. Hopefully not outside the borders of the paint factory.
Jim Thompson:
If it was Johnny Storm's blood it could be relevant. ;-)
Artemus:
And an ATEX microswitch costs less than $100!!!!!! It's more than incredible! Thanks.
a variable reluctance sensor (essentially a permanent magnet with a coil wound round it) detecting the movement of the fan blades or of an impellor driven by the wind. Shunt the sensor with a capacitor large enough to keep the output voltage low enough to not cause a spark (1.2V?) and run a twisted pair back to the detection and display circuit. (alternatively, I guess you could mount the sensor and circuitry indide an explosion-proof box, and run armoured cable to it)
looks fragile and liable to electrostatic generation.
a large fan probably has an induction motor, so no, a current sensor would give an indication of the torque on the motor, a power meter would give even better indication..
-- ?? 100% natural
Who is "Johnny Storm"?
Peter Bent Brigham Hospital (teaching) of Harvard Med School.
Only problem I ever had was when I was confronted by King Saud's bodyguards as I sauntered into the hospital labs in the middle of the night (winter of '61-'62 ;-) ...Jim Thompson
-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et |
Jim Thompson:
The Human Torch of the Fantastic Four.
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