A
Anthony William Sloman
Guest
On Friday, April 7, 2023 at 2:00:33â¯AM UTC+10, Joe Gwinn wrote:
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John Larkin
Guest
On Thu, 6 Apr 2023 11:56:40 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
This would go on a new ethernet VME crate controller board. Bullet
features would include power supply BIST, ambient temp measurement,
and air flow measurement; selling point goodies. Maybe some SMB timing
test connectors on the front panel too. And LEDs. Glitz.
It wouldn\'t have access to the fans, and I\'d like the features to be
small and cheap and low-hassle in production.
It looks like a TO92 transistor, sticking up a ways off the board,
will have a nice theta vs air flow curve. Of course lead thermal
conduction to the PCB pads reduces that. With software switched power
dissipation, we can measure low-power ambient temp and compensate for
that, measure true theta.
The EDN article cited above gives me the theta curve. I need to
measure the thermal time constant. Any guesses?
Yes, some people still use VME.
I guess one could put a differential pressure sensor on the module,
one side inside and one getting air through a hole in the front panel.
Measure crate differential pressure?
<pcdhSpamMeSenseless@electrooptical.net> wrote:
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
This would go on a new ethernet VME crate controller board. Bullet
features would include power supply BIST, ambient temp measurement,
and air flow measurement; selling point goodies. Maybe some SMB timing
test connectors on the front panel too. And LEDs. Glitz.
It wouldn\'t have access to the fans, and I\'d like the features to be
small and cheap and low-hassle in production.
It looks like a TO92 transistor, sticking up a ways off the board,
will have a nice theta vs air flow curve. Of course lead thermal
conduction to the PCB pads reduces that. With software switched power
dissipation, we can measure low-power ambient temp and compensate for
that, measure true theta.
The EDN article cited above gives me the theta curve. I need to
measure the thermal time constant. Any guesses?
Yes, some people still use VME.
I guess one could put a differential pressure sensor on the module,
one side inside and one getting air through a hole in the front panel.
Measure crate differential pressure?
A
Anthony William Sloman
Guest
On Friday, April 7, 2023 at 2:00:33â¯AM UTC+10, Joe Gwinn wrote:
Thermistors are ten times more sensitive than metal film resistance thermometers. You don\'t need to get them all that hot to get a decent sensitivity, and they tend to have specified self-heating coefficients in still air. Interchangeable thermistors are pretty stable, if not all that cheap.
Semiconductor temperature sensors can also work. They tend to be noisier.
--
Bill Sloman, Sydney
On Wed, 05 Apr 2023 21:35:47 -0700, John Larkin
jla...@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.
Thermistors are ten times more sensitive than metal film resistance thermometers. You don\'t need to get them all that hot to get a decent sensitivity, and they tend to have specified self-heating coefficients in still air. Interchangeable thermistors are pretty stable, if not all that cheap.
Semiconductor temperature sensors can also work. They tend to be noisier.
--
Bill Sloman, Sydney
J
John Larkin
Guest
On Thu, 06 Apr 2023 12:00:15 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:
We use leaded ceramic slab and 1206 platinum RTDs, and a cute SOT23
nickel RTD, but they would be down flat on the PC board. I think it
would be better to get the sensor up in the air stream, so the
preferred gadget might be a TO92 transistor.
A 2N4402 costs us 7 cents. An RTD wouldn\'t break the bank, but simple
and cheap are games we play.
wrote:
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
We use leaded ceramic slab and 1206 platinum RTDs, and a cute SOT23
nickel RTD, but they would be down flat on the PC board. I think it
would be better to get the sensor up in the air stream, so the
preferred gadget might be a TO92 transistor.
A 2N4402 costs us 7 cents. An RTD wouldn\'t break the bank, but simple
and cheap are games we play.
L
legg
Guest
On Wed, 05 Apr 2023 21:35:47 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:
Just monitoring temperature in critical locations is usually
sufficient instrumentation for most applications.
Fan tach is ~free, but is misapplied if its absence alone inhibits
function. It\'s a warning only, not a detection of imminent system
failure.
Two point temperature sensing (or single point plus ambient) can
be calibrated to monitor flow, if it\'s really required.
RL
<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?
Just monitoring temperature in critical locations is usually
sufficient instrumentation for most applications.
Fan tach is ~free, but is misapplied if its absence alone inhibits
function. It\'s a warning only, not a detection of imminent system
failure.
Two point temperature sensing (or single point plus ambient) can
be calibrated to monitor flow, if it\'s really required.
RL
L
legg
Guest
On Wed, 05 Apr 2023 21:35:47 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:
Too bad fan mfrs don\'t offer them without magnets or motors, just
tach.
A simple sub into a fan slot would give indications of system air
movement/pressure.
RL
<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?
Too bad fan mfrs don\'t offer them without magnets or motors, just
tach.
A simple sub into a fan slot would give indications of system air
movement/pressure.
RL
B
bitrex
Guest
On 4/6/2023 12:11 PM, John Larkin wrote:
Wow, that schematic is terrible
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.
Wow, that schematic is terrible
J
John Larkin
Guest
On Thu, 06 Apr 2023 12:56:56 -0400, legg <legg@nospam.magma.ca> wrote:
An unpowered fan with tach, run at PWM=0, is an air flow turbine
meter. But my board can\'t access the crate fans and is too small to
have its own fan used as a flow sensor. But it is an interesting idea.
Once long ago, before fan tachs were popular, on some AC powered fans,
I did an electrostatic blade tip sensor to perform essentially the
tach function. Turns out that a spinning plastic blade generates a
nice e field.
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?
Too bad fan mfrs don\'t offer them without magnets or motors, just
tach.
An unpowered fan with tach, run at PWM=0, is an air flow turbine
meter. But my board can\'t access the crate fans and is too small to
have its own fan used as a flow sensor. But it is an interesting idea.
A simple sub into a fan slot would give indications of system air
movement/pressure.
RL
Once long ago, before fan tachs were popular, on some AC powered fans,
I did an electrostatic blade tip sensor to perform essentially the
tach function. Turns out that a spinning plastic blade generates a
nice e field.
J
John Larkin
Guest
On Thu, 6 Apr 2023 12:58:10 -0400, bitrex <user@example.net> wrote:
So bad it\'s fun. A classic.
My equivalent circuit has 4 parts.
On 4/6/2023 12:11 PM, John Larkin wrote:
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.
Wow, that schematic is terrible
So bad it\'s fun. A classic.
My equivalent circuit has 4 parts.
J
Joe Gwinn
Guest
On Thu, 06 Apr 2023 09:39:19 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:
Metallic RTDs are quite stable, and the PTFD form (in the datasheet
above) can stick up 10 mm, which is about the same as a TO-92. One
can compare a SMD version with a nearby PTFD version, canceling local
ambient temp variation.
But the RTDs are ~10 times more expensive than 7 cents. Don\'t know
how much difference that makes in this application.
Joe Gwinn
<jlarkin@highlandSNIPMEtechnology.com> wrote:
On Thu, 06 Apr 2023 12:00:15 -0400, Joe Gwinn <joegwinn@comcast.net
wrote:
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
We use leaded ceramic slab and 1206 platinum RTDs, and a cute SOT23
nickel RTD, but they would be down flat on the PC board. I think it
would be better to get the sensor up in the air stream, so the
preferred gadget might be a TO92 transistor.
A 2N4402 costs us 7 cents. An RTD wouldn\'t break the bank, but simple
and cheap are games we play.
Metallic RTDs are quite stable, and the PTFD form (in the datasheet
above) can stick up 10 mm, which is about the same as a TO-92. One
can compare a SMD version with a nearby PTFD version, canceling local
ambient temp variation.
But the RTDs are ~10 times more expensive than 7 cents. Don\'t know
how much difference that makes in this application.
Joe Gwinn
P
Phil Hobbs
Guest
On 2023-04-06 12:11, John Larkin wrote:
Another possibly interesting approach would be to use a loop of flex
circuit with a SMT thermistor in the middle. A bit of copper pour on the
ends of the thermistor, with little skinny serpentine traces going to
the board, could make the sensor temperature actually track the air
quite well, I\'d expect.
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
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.
Another possibly interesting approach would be to use a loop of flex
circuit with a SMT thermistor in the middle. A bit of copper pour on the
ends of the thermistor, with little skinny serpentine traces going to
the board, could make the sensor temperature actually track the air
quite well, I\'d expect.
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
F
Fred Bloggs
Guest
On Thursday, April 6, 2023 at 12:36:04â¯AM UTC-4, John Larkin wrote:
A piezoelectric air flow sensor is more in line with detecting the presence/ absence of air flow. The signal conditioning then becomes simplified. TI has this crazily named thing:
https://www.ti.com/lit/ug/tidu372/tidu372.pdf
Dunno if that leaf shaped sensor is supposed to flutter or the flexure changes its resonance. Seems I\'ve seen those for sale separately for ~ $10.
System Description
This Piezoelectric Airflow Sensor is intended for
use in systems that require fan airflow detection.
This can include server intake/exhaust airflow
detection, as well as desktop computer airflow.
The Piezoelectric Airflow Sensor design is a
simple, low cost solution which would help
designers who are looking for a means to detect
the presence or absence of fan airflow in existing
systems.
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 piezoelectric air flow sensor is more in line with detecting the presence/ absence of air flow. The signal conditioning then becomes simplified. TI has this crazily named thing:
https://www.ti.com/lit/ug/tidu372/tidu372.pdf
Dunno if that leaf shaped sensor is supposed to flutter or the flexure changes its resonance. Seems I\'ve seen those for sale separately for ~ $10.
System Description
This Piezoelectric Airflow Sensor is intended for
use in systems that require fan airflow detection.
This can include server intake/exhaust airflow
detection, as well as desktop computer airflow.
The Piezoelectric Airflow Sensor design is a
simple, low cost solution which would help
designers who are looking for a means to detect
the presence or absence of fan airflow in existing
systems.
A
a a
Guest
On Thursday, 6 April 2023 at 06:36:04 UTC+2, John Larkin wrote:
and when I power it on, it starts with fans at higher speed to remove debris collected from the air
(really smart solution)
than fans slow down to standard speed (fan in power supply is coming with filter)
So my sugestion is to either control and measure temperature of the air
or control sound of fans, since sound matches constraints in air flow .
I am living on an old Dell PCGiven 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?
and when I power it on, it starts with fans at higher speed to remove debris collected from the air
(really smart solution)
than fans slow down to standard speed (fan in power supply is coming with filter)
So my sugestion is to either control and measure temperature of the air
or control sound of fans, since sound matches constraints in air flow .
J
John Larkin
Guest
On Thu, 6 Apr 2023 16:11:51 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
In a given crate, the air flow might go in any direction, which could
affect the loop. The classic below-the-boards fan tray can create
bizarre flow patterns. I\'d expect the flow speed and direction to vary
in different places on the board, too, so I guess I\'d go for the
middle. A TO92 is a reasonable approximation to a cylinder.
The weather has been really weird here lately. Yesterday we had three
distinct cloud layers, moving in different directions. Air is evil.
<pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2023-04-06 12:11, John Larkin wrote:
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.
Another possibly interesting approach would be to use a loop of flex
circuit with a SMT thermistor in the middle. A bit of copper pour on the
ends of the thermistor, with little skinny serpentine traces going to
the board, could make the sensor temperature actually track the air
quite well, I\'d expect.
Cheers
Phil Hobbs
In a given crate, the air flow might go in any direction, which could
affect the loop. The classic below-the-boards fan tray can create
bizarre flow patterns. I\'d expect the flow speed and direction to vary
in different places on the board, too, so I guess I\'d go for the
middle. A TO92 is a reasonable approximation to a cylinder.
The weather has been really weird here lately. Yesterday we had three
distinct cloud layers, moving in different directions. Air is evil.
J
John Larkin
Guest
On Thu, 06 Apr 2023 13:51:54 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:
That\'s a good price. We have an essentially identical Minco part in
stock that costs $4. But it would be flimsy to mount on a board,
sticking up into the air flow. And it needs to self-heat to measure
flow.
I guess I could do my sequenced heat and cool time constant
measurement on it.
Not a big deal, but may as well save money if it doesn\'t take a huge
hassle.
wrote:
On Thu, 06 Apr 2023 09:39:19 -0700, John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote:
On Thu, 06 Apr 2023 12:00:15 -0400, Joe Gwinn <joegwinn@comcast.net
wrote:
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
We use leaded ceramic slab and 1206 platinum RTDs, and a cute SOT23
nickel RTD, but they would be down flat on the PC board. I think it
would be better to get the sensor up in the air stream, so the
preferred gadget might be a TO92 transistor.
A 2N4402 costs us 7 cents. An RTD wouldn\'t break the bank, but simple
and cheap are games we play.
Metallic RTDs are quite stable, and the PTFD form (in the datasheet
above) can stick up 10 mm, which is about the same as a TO-92. One
can compare a SMD version with a nearby PTFD version, canceling local
ambient temp variation.
That\'s a good price. We have an essentially identical Minco part in
stock that costs $4. But it would be flimsy to mount on a board,
sticking up into the air flow. And it needs to self-heat to measure
flow.
I guess I could do my sequenced heat and cool time constant
measurement on it.
But the RTDs are ~10 times more expensive than 7 cents. Don\'t know
how much difference that makes in this application.
Not a big deal, but may as well save money if it doesn\'t take a huge
hassle.
Joe Gwinn
J
John Larkin
Guest
On Thu, 6 Apr 2023 14:41:35 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:
That\'s insanely complex. Not hardly \"simple, low cost.\"
Do you have any idea how the piezo sensors measure air flow?
<bloggs.fredbloggs.fred@gmail.com> wrote:
On Thursday, April 6, 2023 at 12:36:04?AM UTC-4, 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?
A piezoelectric air flow sensor is more in line with detecting the presence/ absence of air flow. The signal conditioning then becomes simplified. TI has this crazily named thing:
https://www.ti.com/lit/ug/tidu372/tidu372.pdf
Dunno if that leaf shaped sensor is supposed to flutter or the flexure changes its resonance. Seems I\'ve seen those for sale separately for ~ $10.
System Description
This Piezoelectric Airflow Sensor is intended for
use in systems that require fan airflow detection.
This can include server intake/exhaust airflow
detection, as well as desktop computer airflow.
The Piezoelectric Airflow Sensor design is a
simple, low cost solution which would help
designers who are looking for a means to detect
the presence or absence of fan airflow in existing
systems.
That\'s insanely complex. Not hardly \"simple, low cost.\"
Do you have any idea how the piezo sensors measure air flow?
P
Phil Hobbs
Guest
On 2023-04-06 19:06, John Larkin wrote:
It\'s your gizmo, of course, but to me, a sensor that has a 90:10 air vs
board temperature seems likely to be less bothered by mild to moderate
airflow pattern disturbances than one that\'s 10:90.
The old National Semi temperature sensing handbook has a lot of good
info about using plastic packaged ICs (mostly TO-92) for air temperature
sending.
<https://electrooptical.net/www/appnotes/NationalSemiTemperatureMeasurementHandbook2007.pdf>.
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
On Thu, 6 Apr 2023 16:11:51 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2023-04-06 12:11, John Larkin wrote:
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.
Another possibly interesting approach would be to use a loop of flex
circuit with a SMT thermistor in the middle. A bit of copper pour on the
ends of the thermistor, with little skinny serpentine traces going to
the board, could make the sensor temperature actually track the air
quite well, I\'d expect.
Cheers
Phil Hobbs
In a given crate, the air flow might go in any direction, which could
affect the loop. The classic below-the-boards fan tray can create
bizarre flow patterns. I\'d expect the flow speed and direction to vary
in different places on the board, too, so I guess I\'d go for the
middle. A TO92 is a reasonable approximation to a cylinder.
The weather has been really weird here lately. Yesterday we had three
distinct cloud layers, moving in different directions. Air is evil.
It\'s your gizmo, of course, but to me, a sensor that has a 90:10 air vs
board temperature seems likely to be less bothered by mild to moderate
airflow pattern disturbances than one that\'s 10:90.
The old National Semi temperature sensing handbook has a lot of good
info about using plastic packaged ICs (mostly TO-92) for air temperature
sending.
<https://electrooptical.net/www/appnotes/NationalSemiTemperatureMeasurementHandbook2007.pdf>.
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
J
Jasen Betts
Guest
On 2023-04-06, legg <legg@nospam.magma.ca> wrote:
You still need a magnet to operate the Hall sensor, but yeah you
could loose the stator and have an anemometer. BTDT
--
Jasen.
ðºð¦ Слава УкÑаÑнÑ
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?
Too bad fan mfrs don\'t offer them without magnets or motors, just
tach.
You still need a magnet to operate the Hall sensor, but yeah you
could loose the stator and have an anemometer. BTDT
A simple sub into a fan slot would give indications of system air
movement/pressure.
RL
--
Jasen.
ðºð¦ Слава УкÑаÑнÑ
J
John Larkin
Guest
On Thu, 6 Apr 2023 19:47:00 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
An LM35 could be persuaded to self-heat I guess, load it pretty hard
and vary Vcc. But I don\'t like to run them above 5 volts.
<pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2023-04-06 19:06, John Larkin wrote:
On Thu, 6 Apr 2023 16:11:51 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:
On 2023-04-06 12:11, John Larkin wrote:
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.
Another possibly interesting approach would be to use a loop of flex
circuit with a SMT thermistor in the middle. A bit of copper pour on the
ends of the thermistor, with little skinny serpentine traces going to
the board, could make the sensor temperature actually track the air
quite well, I\'d expect.
Cheers
Phil Hobbs
In a given crate, the air flow might go in any direction, which could
affect the loop. The classic below-the-boards fan tray can create
bizarre flow patterns. I\'d expect the flow speed and direction to vary
in different places on the board, too, so I guess I\'d go for the
middle. A TO92 is a reasonable approximation to a cylinder.
The weather has been really weird here lately. Yesterday we had three
distinct cloud layers, moving in different directions. Air is evil.
It\'s your gizmo, of course, but to me, a sensor that has a 90:10 air vs
board temperature seems likely to be less bothered by mild to moderate
airflow pattern disturbances than one that\'s 10:90.
The old National Semi temperature sensing handbook has a lot of good
info about using plastic packaged ICs (mostly TO-92) for air temperature
sending.
https://electrooptical.net/www/appnotes/NationalSemiTemperatureMeasurementHandbook2007.pdf>.
Cheers
Phil Hobbs
An LM35 could be persuaded to self-heat I guess, load it pretty hard
and vary Vcc. But I don\'t like to run them above 5 volts.
W
whit3rd
Guest
On Thursday, April 6, 2023 at 2:53:08â¯AM UTC-7, John Larkin wrote:
Yeah, that can work; it also measures air density, though; do you
control for altitude differences?
> >>Carbon comp resistor?
Worst tempco possible (very low, compared to most materials)
any thermistor would be better. Best would be two thermistors, one
with a windshield and the other in free air, so ambient temperature
can vary without changing the sensitivity. That\'s half a bridge,
and any low-offset op amp can give you a useful indication.
Yeah, but... what kind of current would you need to bias it for significant self-heating?
I\'d think of a small weathervane with a propellor-optosensor, or an array of directional vanes
with spring bias; if there\'s airflow enough to align the array against the bias, you have airflow!
Stretching the imagination, put some bright colored streamers on the vent port, and aim a
webcam at that. Only takes one electrical appliance to monitor a whole rack.
An instrumented fan, too, could warn of a clogged filter by the alteration of its power usage.
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.
Yeah, that can work; it also measures air density, though; do you
control for altitude differences?
> >>Carbon comp resistor?
Worst tempco possible (very low, compared to most materials)
any thermistor would be better. Best would be two thermistors, one
with a windshield and the other in free air, so ambient temperature
can vary without changing the sensitivity. That\'s half a bridge,
and any low-offset op amp can give you a useful indication.
This can\'t be a new problem. Any other suggestions?
Any silly-con diode is a few mV per degree C.
Yeah, but... what kind of current would you need to bias it for significant self-heating?
I\'d think of a small weathervane with a propellor-optosensor, or an array of directional vanes
with spring bias; if there\'s airflow enough to align the array against the bias, you have airflow!
Stretching the imagination, put some bright colored streamers on the vent port, and aim a
webcam at that. Only takes one electrical appliance to monitor a whole rack.
An instrumented fan, too, could warn of a clogged filter by the alteration of its power usage.