air flow sensor on PCB...

[John Larkin]

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

 

[Jan Panteltje]

On a sunny day (Wed, 05 Apr 2023 21:35:47 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<3cis2i157dnuocerhi87c4ddi8l8g58nsp@4ax.com>:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

Any silly-con diode is a few mV per degree C.
One sticking in the air from some through-holes in the peeseebee.
___
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= |
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======|===|====

 

[Jan Panteltje]

On a sunny day (Wed, 05 Apr 2023 21:35:47 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<3cis2i157dnuocerhi87c4ddi8l8g58nsp@4ax.com>:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

Any silly-con diode is a few mV per degree C.
One sticking in the air from some through-holes in the peeseebee.
___
| |
= |
|.| |
| | |
= |
| |
======|===|====

PS
a LM35 mounted the same way can be read by your efpeegeeaa
and gives you almost exact temperature.

 

[Anthony William Sloman]

On Thursday, April 6, 2023 at 2:36:04 PM UTC+10, John Larkin wrote:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

Negative temperature coefficient thermistors are about an order of magnitude more sensitive to temperature change than metal film resistance thermometer elements and tend to have specified self-heating constants in still air. A leaded glass-bead thermistor should work.

--
Bill Sloman, Sydney

 

[John Larkin]

On Thu, 06 Apr 2023 04:59:42 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Wed, 05 Apr 2023 21:35:47 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
3cis2i157dnuocerhi87c4ddi8l8g58nsp@4ax.com>:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

Any silly-con diode is a few mV per degree C.
One sticking in the air from some through-holes in the peeseebee.
___
| |
= |
|.| |
| | |
= |
| |
======|===|====

PS
a LM35 mounted the same way can be read by your efpeegeeaa
and gives you almost exact temperature.

Temperature is easy. I want to measure air flow.

I was thinking about something physically like your sketch. A leaded
diode, a leaded carbon resistor, a TO92 device, something like that.

But instead of measuring some dissipation coefficient, we could
measure its thermal time constant. Measure some surrogate of
temperature. Apply a lot of heat for a while, shut it off, and measure
the temperature thing vs time as it cools.

A dpak transistor with winged heat sink would be interesting.
Dissipate a bunch of power for a while then use the b-e junction as a
thermometer and watch it cool down.

Or I guess one could just measure heat sink theta based on a sequence
of measurements. Same idea, almost.

https://www.dropbox.com/s/gafatsddcprrxuc/7106DG%20-%20Board%20level%20heatsinks.pdf?dl=0

 

[John Larkin]

On Wed, 05 Apr 2023 21:35:47 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

This might work. Tad expensive, sole source.

https://www.mouser.com/ProductDetail/Renesas-Electronics/FS3000-1015?qs=DPoM0jnrROUTWmVgwVMpEQ%3D%3D

 

[Lasse Langwadt Christensen]

torsdag den 6. april 2023 kl. 06.36.04 UTC+2 skrev John Larkin:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

a bridge with two RTDs/NTCs, one of them in the air flow the other shielded from the airflow?

 

[Jan Panteltje]

On a sunny day (Thu, 06 Apr 2023 02:52:52 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<i44t2i5k59rbd7va6m5eefbom222stf341@4ax.com>:

On Thu, 06 Apr 2023 04:59:42 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Wed, 05 Apr 2023 21:35:47 -0700) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
3cis2i157dnuocerhi87c4ddi8l8g58nsp@4ax.com>:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

Any silly-con diode is a few mV per degree C.
One sticking in the air from some through-holes in the peeseebee.
___
| |
= |
|.| |
| | |
= |
| |
======|===|====

PS
a LM35 mounted the same way can be read by your efpeegeeaa
and gives you almost exact temperature.

Temperature is easy. I want to measure air flow.

I was thinking about something physically like your sketch. A leaded
diode, a leaded carbon resistor, a TO92 device, something like that.

But instead of measuring some dissipation coefficient, we could
measure its thermal time constant. Measure some surrogate of
temperature. Apply a lot of heat for a while, shut it off, and measure
the temperature thing vs time as it cools.

A dpak transistor with winged heat sink would be interesting.
Dissipate a bunch of power for a while then use the b-e junction as a
thermometer and watch it cool down.

Or I guess one could just measure heat sink theta based on a sequence
of measurements. Same idea, almost.

https://www.dropbox.com/s/gafatsddcprrxuc/7106DG%20-%20Board%20level%20heatsinks.pdf?dl=0

There is also the ultrasonic wind speed meter:
https://panteltje.nl/pub/wind_speed_by_differential_2_ebay_distance_meters_IMG_4891.JPG

And I did this to measure wind direction and speed:
https://panteltje.nl/panteltje/pic/wind_pic_thermal_udp/
4 diodes basically.
Works sort of..

Ultrasonic is very exact:
https://panteltje.nl/pub/44kHz_radar_time_of_flight_test_in_wind_tunnel_IMG_4105.JPG
The ebay ultrasonic distance measurement modules are ony 2 or 3 USD IIRC.

I also have one with a propeller in it ... for on a sailboat.

Did quite a few experiments with air flow.
Look at phase shift between ultrasonic sensors

Use wget perhaps to download this video that shows the phase shift for various speed:
http://panteltje.nl/pub/44kHz_Doppler_phase_change_in_wind_tunnel_with_vane_MVI_4113.AVI

 

[Phil Hobbs]

On 2023-04-06 00:35, John Larkin wrote:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

Hot wires are quick and simple. As an extra bonus, if you pick the
right excitation frequency you can get rid of the poorly-controlled
sensor-to-board thermal conduction effect.

What\'s such a nuisance about it?

-- Cutting the bulb?
-- Soldering the leads?
-- Calibration?

Or something else?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Rich S]

On Thursday, April 6, 2023 at 1:19:04 PM UTC, Phil Hobbs wrote:

On 2023-04-06 00:35, John Larkin wrote:
Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

this is cute idea, and cheap
https://www.edn.com/linearized-portable-anemometer-with-thermostated-darlington-pair/
regards, RS

 

[Rich S]

On Thursday, April 6, 2023 at 1:27:48 PM UTC, Rich S wrote:

On Thursday, April 6, 2023 at 1:19:04 PM UTC, Phil Hobbs wrote:
On 2023-04-06 00:35, John Larkin wrote:
Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

this is cute idea, and cheap
https://www.edn.com/linearized-portable-anemometer-with-thermostated-darlington-pair/
regards, RS

and Mr Woodward\'s simpler circuit, if you just need a binary output (instead of linear analog)
https://www.edn.com/self-heated-darlington-transistor-pair-comprises-new-air-flow-sensor
=RS

 

[Anthony William Sloman]

On Thursday, April 6, 2023 at 7:53:08 PM UTC+10, John Larkin wrote:

On Thu, 06 Apr 2023 04:59:42 GMT, Jan Panteltje <al...@comet.invalid
wrote:
On a sunny day (Wed, 05 Apr 2023 21:35:47 -0700) it happened John Larkin
jla...@highlandSNIPMEtechnology.com> wrote in
3cis2i157dnuocerh...@4ax.com>:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

<snip>

> Temperature is easy. I want to measure air flow.

Self-heating depends on air-flow.

The dissipating device dissipitates some of it\'s heat by warming up the air in contact with its surface.

It that air is moving it dissipates more heat.

Stuff that is flat on the board dissipates into the bottom of the boundary layer, which doesn\'t move all that fast.

If the devices stick up about the board, it\'s in faster moving air. It the air is moving fast enough it becomes turbulent, and shifts more heat.

I was thinking about something physically like your sketch. A leaded diode, a leaded carbon resistor, a TO92 device, something like that.

But instead of measuring some dissipation coefficient, we could measure its thermal time constant.

It\'s the same thing. The thermal time constatnt is just the product of the thermal mass of the device and the thermal resistance to anbient, which is to say the dissipation coefficient.

> Measure some surrogate of temperature.

Resistance thermometers and thermistors use resistance as a surrogate for temperature.

> Apply a lot of heat for a while, shut it off, and measure the temperature thing vs time as it cools.

What does it win you?

> A dpak transistor with winged heat sink would be interesting.

But bulky. Again, what doe sit win you.

Dissipate a bunch of power for a while then use the b-e junction as a thermometer and watch it cool down.

Or I guess one could just measure heat sink theta based on a sequence of measurements. Same idea, almost.

Exactly the same idea.

<snipped an image of a heatr sink>

--
Bill Sloman, Sydney

 

[John Larkin]

On Thu, 6 Apr 2023 09:18:47 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-04-06 00:35, John Larkin wrote:
Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?


Hot wires are quick and simple. As an extra bonus, if you pick the
right excitation frequency you can get rid of the poorly-controlled
sensor-to-board thermal conduction effect.

What\'s such a nuisance about it?

-- Cutting the bulb?
-- Soldering the leads?
-- Calibration?

Or something else?

Cheers

Phil Hobbs

Breaking a light bulb tends to be erratic; we\'ve done that. And a
nasty production process. It looks ugly too.

We sure don\'t want to calibrate an air flow sensor. The flow sense
would be a selling feature, a fan+filter check, so we\'d want decent
accuracy as-built.

 

[Anthony William Sloman]

On Friday, April 7, 2023 at 12:24:08 AM UTC+10, John Larkin wrote:

On Thu, 6 Apr 2023 09:18:47 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

On 2023-04-06 00:35, John Larkin wrote:
Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

Hot wires are quick and simple. As an extra bonus, if you pick the
right excitation frequency you can get rid of the poorly-controlled
sensor-to-board thermal conduction effect.

What\'s such a nuisance about it?

-- Cutting the bulb?
-- Soldering the leads?
-- Calibration?

Or something else?

Breaking a light bulb tends to be erratic; we\'ve done that. And a
nasty production process. It looks ugly too.

A thermistor would do the same job - rather better - and looks neater.

> We sure don\'t want to calibrate an air flow sensor.

You haven\'t got a lot of choice.

> The flow sense would be a selling feature, a fan+filter check, so we\'d want decent accuracy as-built.

Then you probably need a turbine meter, or an ultrasonic flow meter that will actually measure just the air speed.

I once worked on a vortex shedding flow meter - it only works for turbulent flows and you don\'t seem to be looking at that kind of airflow, but it was linear and remarkably precise, if hideousy expensive and somewhat bulky.

--
Bill Sloman, Sydney

 

[Jan Panteltje]

On a sunny day (Thu, 06 Apr 2023 02:52:52 -0700) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<i44t2i5k59rbd7va6m5eefbom222stf341@4ax.com>:

PS
So one like this:
https://www.ebay.com/itm/322948018241
the output is a pulse representing the delay time.
In this form it uses the reflected pulse by some object
so wind back and wind against cancels.

I removed the receive sensor and put it at some distance facing the transmit module
now it no longer looks for the reflected pulse, but the tranmited one
so airspeed due to wind no longer cancels.
The output pulse should be easy to monitor with your efpeegeeaa

Not bad for 1 dollar 38 cents!
Bit of soldering...
Math is easy: speed of sound, distance..

 

[John Larkin]

On Thu, 6 Apr 2023 06:27:44 -0700 (PDT), Rich S
<richsulinengineer@gmail.com> wrote:

On Thursday, April 6, 2023 at 1:19:04?PM UTC, Phil Hobbs wrote:
On 2023-04-06 00:35, John Larkin wrote:
Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?


this is cute idea, and cheap
https://www.edn.com/linearized-portable-anemometer-with-thermostated-darlington-pair/
regards, RS

That\'s a nice curve, thanks. I was going to measure that myself. Both
your cited curves align with the data sheet value of 200 K/W for a
TO92 in still air, and I figure we\'ll have about 200 fpm air flow.

I did this last night, before (cross-my-heart hope-to-die) I saw your
posts.

https://www.dropbox.com/s/9jfhy9d74v1njjd/Air_Flow_TO92.jpg?raw=1

We could turn on the SSR and heat up the transistor, and then turn it
off and measure Vbe as it cools down. The flow measurement is
essentially independent of ambient temperature and the parts cost is
under a dollar. \"SSR\" could be a couple of discretes and make it even
cheaper.

I guess I\'d note to manufacturing to use some long, specified lead
length on the PNP.

I\'ll have a 1 GHz quad-core ARM not working hard, so we can apply lots
of software. And the product will have a multiplexed 12-bit ADC
already.

But other ideas might be fun too.

 

[Clive Arthur]

On 06/04/2023 05:35, John Larkin wrote:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?

Another way is to measure the temperature of air rising from some
normally warm part. If the wind blows, the convected airstream goes
away and the measured temperature drops.

Bit of a silly idea, but hey.

--
Cheers
Clive

 

[Phil Hobbs]

On 2023-04-06 10:23, John Larkin wrote:

On Thu, 6 Apr 2023 09:18:47 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-04-06 00:35, John Larkin wrote:
Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?


Hot wires are quick and simple. As an extra bonus, if you pick the
right excitation frequency you can get rid of the poorly-controlled
sensor-to-board thermal conduction effect.

What\'s such a nuisance about it?

-- Cutting the bulb?
-- Soldering the leads?
-- Calibration?

Or something else?


Breaking a light bulb tends to be erratic; we\'ve done that. And a
nasty production process. It looks ugly too.

We sure don\'t want to calibrate an air flow sensor. The flow sense
would be a selling feature, a fan+filter check, so we\'d want decent
accuracy as-built.

The issue is always that the sensor measures its own temperature, which
is only obliquely connected to what you care about. Copper lead wires
tend to make that track the board temperature much more closely than air
temperature.

One approach would be to use a couple of SMT barometric pressure
sensors, (MS560702BA03-50 is a fave of ours) to measure the pressure
drop across the filter. How easy that is to do will depend fairly
sensitively on the physical layout, of course.

For a go/no go measurement, fan current is another possibility.

But an AC measurement with a broken tungsten bulb is surprisingly good.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Joe Gwinn]

On Wed, 05 Apr 2023 21:35:47 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

One can get 1000-ohm platinum RTDs for small dollars:

..<https://www.newark.com/te-connectivity-sensors/nb-ptco-012/rtd-sensor-thin-film-platinum/dp/03AC1640>

If the issue is just to tell if there is a lot of airflow, the
temperature delta does not need to be large, so a simple bridge with
AC source and synchronous detector should work.

Cheaper still are RTDs made of nickel, versus platinum. Nickel is OK
if the temperature in still air isn\'t too high.

Joe Gwinn

 

[John Larkin]

On Thu, 6 Apr 2023 16:53:46 +0100, Clive Arthur
<clive@nowaytoday.co.uk> wrote:

On 06/04/2023 05:35, John Larkin wrote:
Given a PC board in a crate, like PCIe or PXI or VME or something,
what would be a good way to check air flow across the board, to verify
that the box fans and filters are OK? Assume this board can\'t access
the fan tachs or anything like that.

I was thinking that I might stick a small thinfilm RTD in the air
stream and measure its temperature at two different voltages, to
estimate its self-heating, which would vary with air flow.

The classic broken light bulb hot-wire anemometer is a nuisance.

Carbon comp resistor?

This can\'t be a new problem. Any other suggestions?


Another way is to measure the temperature of air rising from some
normally warm part. If the wind blows, the convected airstream goes
away and the measured temperature drops.

Bit of a silly idea, but hey.

Not silly, but the hassle is implementation. We once made a flow
sensor based on one part heating another part downstream in the air
flow, and it wasn\'t reliable.

My current thinking is to measure the theta of a part sticking up off
the board, where theta is temp rise in degrees C per watt. That will
drop as air flow increases.

The game is to make that as cheap and simple and as manufacturable as
possible.

I was just looking at the EDN article cited above, and noticed the
schematic in fig 2.

https://www.edn.com/linearized-portable-anemometer-with-thermostated-darlington-pair/

One could list the several horrors.