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ATEX air flow sensor

F

F. Bertolazzi

Jan 1, 1970
0
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.
 
J

JB

Jan 1, 1970
0
F. Bertolazzi said:
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
 
F

F. Bertolazzi

Jan 1, 1970
0
JB:
*Anything* which is ATEX approved is going to be expensive.
You may be unlucky in your search.

Clearly I meant "APEX inexpensive". $500 would be great, $100 incredible.
 
F

F. Bertolazzi

Jan 1, 1970
0
Jim Thompson:
What _type_ of fan?

About 2 feet diameter, used, with other two, to ventilate a 100 ft.
underground passage in case of gas leakage.
 
F

F. Bertolazzi

Jan 1, 1970
0
Jim Thompson:
Maybe something as simple as a Hall sensor to detect the fan blade
going by?

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:
http://www.instructables.com/id/Windbelt-Redux--21st-Century-Micro-Power-Generatio/

I was also thinking about looking in the power supply and see if the moving
motor distorts the sine wave when moving.
But detecting air flow itself can get tricky.

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.
 
A

Artemus

Jan 1, 1970
0
Jon Elson said:
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
 
F

F. Bertolazzi

Jan 1, 1970
0
[email protected]:
two self heated NTCs in a bridge, on shielded from the airflow, one in
the airflow.

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.
a differential air pressure sensor, freescale has some with hose
connections so
the electronics doesn't have to be in or near the duct

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.
 
A

Artemus

Jan 1, 1970
0
F. Bertolazzi said:
[email protected]:


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
 
F

F. Bertolazzi

Jan 1, 1970
0
Artemus:
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.

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".
 
F

F. Bertolazzi

Jan 1, 1970
0
[email protected]:
a differential air pressure sensor, freescale has some with hose
connections so
the electronics doesn't have to be in or near the duct

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.
 
F

F. Bertolazzi

Jan 1, 1970
0
Jim Thompson:
Read my 1962 MIT thesis... except I was measuring blood flow ;-)

If it was Johnny Storm's blood it could be relevant. ;-)
 
F

F. Bertolazzi

Jan 1, 1970
0
Artemus:
A swinging vane and a microswitch is a low tech solution that
almost anyone could diagnose and fix a problem with.

And an ATEX microswitch costs less than $100!!!!!!
It's more than incredible! Thanks.
 
J

Jasen Betts

Jan 1, 1970
0
Jim Thompson:


The problem is that ATEX thing, otherwise even a simple piece of plastic
with two strain gauges tacked on could work.

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.
I was also thinking about looking in the power supply and see if the moving
motor distorts the sine wave when moving.

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..
 
S

Sjouke Burry

Jan 1, 1970
0
F. Bertolazzi said:
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.
I have used a small flap with a glued on small magnet,
to close a reed relay, when air stops moving.
 
F

F. Bertolazzi

Jan 1, 1970
0
Sjouke Burry:
I have used a small flap with a glued on small magnet,
to close a reed relay, when air stops moving.

I will use, instead of the magnet+reed, an ATEX compliant microswitch, so I
can "inherit" theswitch's Ex marking, hoping I don't run into a
hair-splitting inspector.
 
L

legg

Jan 1, 1970
0
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.

In a duct, with fair air flow, you can build one with a microswitch
and a 'sail'.

RL
 
J

Jamie

Jan 1, 1970
0
BobS said:
Commercial sensors for HVAC maybe suitable. Take a look at what Dwyer
has.
Two resistor wires in the path, one open to the path of air flow, one
blocked but in the same vicinity. These become part of a balanced bridge
circuit into a high gain comparator or, a low gain one depending on the
type of wire you are using..

Jamie
 
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