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mike
Guest
Sat Jan 07, 2012 11:43 pm
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
John Larkin
Guest
Sat Jan 07, 2012 11:53 pm
On Sat, 07 Jan 2012 14:43:03 -0800, mike <spamme9_at_gmail.com> wrote:
Quote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
There are cheap differential pressure sensors around that work in this
range.
John
Joerg
Guest
Sat Jan 07, 2012 11:58 pm
mike wrote:
Quote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
A vane? Essentially a small plate that sits in a square profile, with a
position sensor that signals when it's in the middle (meaning no flow in
either direction). Can be centered by gravity and then balanced around
the pivot, but not completely. How much you balance it determines its
sensitivity, to some extent.
Of course it'll react to pressure from the wind but so will just about
anything else.
--
Regards, Joerg
http://www.analogconsultants.com/
Artemus
Guest
Sun Jan 08, 2012 12:20 am
"mike" <spamme9_at_gmail.com> wrote in message news:jeahro$ar4$1_at_dont-email.me...
Quote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
A diaphragm is simple, doesn't require a flow to maintain it's position
and is easy to dampen mechanically. Position sensing can be as simple
as a pair of point contacts or as complex as you want to make it.
Art
Bill Sloman
Guest
Sun Jan 08, 2012 1:17 am
On Jan 7, 11:43 pm, mike <spam...@gmail.com> wrote:
Quote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
I don't think that there is anything simple that would work. When I
was a graduate student the best way of doing it seemed to be with a
stretched conductive (and grounded) diaphragm between two closely
spaced flat electrodes.
You set up a capacitance bridge, with the capacitance from the
electrodes to ground as one side of the bridge, and a centre tapped
transformer as the other. The net excursion at the centre-tap was
proportional to bridge imbalance - zero at balance, in-phase on one
side and anti-phase on the other.
For added extra capacity you could apply high DC voltages to each of
the electrodes and adjust them up and down to apply a compensating
electrostatic force to the diaphragm. If you over-did it, the
diaphragm distorted itself into hills and valleys.
Baratron was the industry leader back then, and still seems to be in
business. I don't recall them doing electrostatic pressure
compensation - it only works for very low differential pressures.
http://www.mksinst.com/product/category.aspx?categoryid=72
--
Bill Sloman, Nijmegen
George Herold
Guest
Sun Jan 08, 2012 2:15 am
On Jan 7, 5:53 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote:
On Sat, 07 Jan 2012 14:43:03 -0800, mike <spam...@gmail.com> wrote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
There are cheap differential pressure sensors around that work in this
range.
John- Hide quoted text -
- Show quoted text -
We use a honeywell differential pressure gizmo. I think it sells for ~
$15.
(Newark carries them.)
George H.
who where
Guest
Sun Jan 08, 2012 2:21 am
On Sat, 07 Jan 2012 14:43:03 -0800, mike <spamme9_at_gmail.com> wrote:
Quote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
How much closer than 0.01" WG do you want? And do you realise the
impact of opening or closing a door on any hypersensitive
gauge/transducer?
John Larkin
Guest
Sun Jan 08, 2012 2:31 am
On Sat, 7 Jan 2012 16:15:59 -0800 (PST), George Herold
<gherold_at_teachspin.com> wrote:
Quote:
On Jan 7, 5:53 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Sat, 07 Jan 2012 14:43:03 -0800, mike <spam...@gmail.com> wrote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
There are cheap differential pressure sensors around that work in this
range.
John- Hide quoted text -
- Show quoted text -
We use a honeywell differential pressure gizmo. I think it sells for ~
$15.
(Newark carries them.)
George H.
Right, like that. Motorola used to make similar things once, but they
spun that off to somebody.
I've seen both linear sensor and switch types. The switches are even
cheaper.
John
mike
Guest
Sun Jan 08, 2012 1:24 pm
George Herold wrote:
Quote:
On Jan 7, 5:53 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Sat, 07 Jan 2012 14:43:03 -0800, mike <spam...@gmail.com> wrote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
There are cheap differential pressure sensors around that work in this
range.
John- Hide quoted text -
- Show quoted text -
We use a honeywell differential pressure gizmo. I think it sells for ~
$15.
(Newark carries them.)
George H.
Thanks, but the low pressure versions are $72 and digital, so I need a
microprocessor
and a circuit board and power supply and box to put it in and code to run it
and some kind of display....And I've already got that: Omega PCL-200.
I was hoping for a creative option similar in complexity to what I
described.
I've got a UEI EM150. Gonna see what happens when I try to increase
the gain X10.
John Devereux
Guest
Sun Jan 08, 2012 3:20 pm
John Larkin <jjlarkin_at_highNOTlandTHIStechnologyPART.com> writes:
Quote:
On Sat, 7 Jan 2012 16:15:59 -0800 (PST), George Herold
gherold_at_teachspin.com> wrote:
On Jan 7, 5:53Â pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Sat, 07 Jan 2012 14:43:03 -0800, mike <spam...@gmail.com> wrote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Â Stuffed it all into the side of a plastic
tube. Â Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. Â The thermistors
are tiny, but they're encapsulated in kapton tape. Â Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
There are cheap differential pressure sensors around that work in this
range.
John- Hide quoted text -
- Show quoted text -
We use a honeywell differential pressure gizmo. I think it sells for ~
$15.
(Newark carries them.)
George H.
Right, like that. Motorola used to make similar things once, but they
spun that off to somebody.
Freescale AFAIK
Quote:
I've seen both linear sensor and switch types. The switches are even
cheaper.
John
--
John Devereux
Don Lancaster
Guest
Mon Jan 09, 2012 5:12 am
On 1/8/2012 7:20 AM, John Devereux wrote:
Quote:
John Larkin<jjlarkin_at_highNOTlandTHIStechnologyPART.com> writes:
On Sat, 7 Jan 2012 16:15:59 -0800 (PST), George Herold
gherold_at_teachspin.com> wrote:
On Jan 7, 5:53 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Sat, 07 Jan 2012 14:43:03 -0800, mike<spam...@gmail.com> wrote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
There are cheap differential pressure sensors around that work in this
range.
John- Hide quoted text -
- Show quoted text -
We use a honeywell differential pressure gizmo. I think it sells for ~
$15.
(Newark carries them.)
George H.
Right, like that. Motorola used to make similar things once, but they
spun that off to somebody.
Freescale AFAIK
I've seen both linear sensor and switch types. The switches are even
cheaper.
John
Dwyer has all sorts of stuff for this.
<
http://www.dwyer-inst.com/ >
--
Many thanks,
Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss:
http://www.tinaja.com/whtnu.xml email: don_at_tinaja.com
Please visit my GURU's LAIR web site at
http://www.tinaja.com
whit3rd
Guest
Mon Jan 09, 2012 8:14 am
On Saturday, January 7, 2012 2:43:03 PM UTC-8, mike wrote:
Quote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
So, you want a manometer that indicates 'positive', 'negative' , and 'near
zero'?
Make a manometer of the diaphragm type, and have the center of the
diaphragm operate a pair of (over-under) switches. To protect
from gusts and surges, just use a narrow tube to 'outdoors' and
let air viscosity work for you.
With a light-colored diaphragm, the switches could operate
on light reflection.
George Herold
Guest
Mon Jan 09, 2012 4:28 pm
On Jan 8, 7:24 am, mike <spam...@gmail.com> wrote:
Quote:
George Herold wrote:
On Jan 7, 5:53 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Sat, 07 Jan 2012 14:43:03 -0800, mike <spam...@gmail.com> wrote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
There are cheap differential pressure sensors around that work in this
range.
John- Hide quoted text -
- Show quoted text -
We use a honeywell differential pressure gizmo. I think it sells for ~
$15.
(Newark carries them.)
George H.
Thanks, but the low pressure versions are $72 and digital, so I need a
microprocessor
and a circuit board and power supply and box to put it in and code to run it
and some kind of display....And I've already got that: Omega PCL-200.
I was hoping for a creative option similar in complexity to what I
described.
I've got a UEI EM150. Gonna see what happens when I try to increase
the gain X10.- Hide quoted text -
- Show quoted text -
Hi Mike, Looks like the last time we bought these they came from
digikey. part number 480-2516-ND. (The price has gone up a bit since
the first purchase.) They make different sensitivities. I stuck an
instrument amp across it. I’m not sure how much gain... I could look
up the circuit.
I would guess maybe something like 10V full scale.
George H.
George Herold
Guest
Mon Jan 09, 2012 6:03 pm
On Jan 9, 9:28 am, George Herold <gher...@teachspin.com> wrote:
Quote:
On Jan 8, 7:24 am, mike <spam...@gmail.com> wrote:
George Herold wrote:
On Jan 7, 5:53 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Sat, 07 Jan 2012 14:43:03 -0800, mike <spam...@gmail.com> wrote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
Best pressure gauge I have has a resolution of 0.01" of water.
I'd like something simpler I could leave hooked up and running.
I started with a heated resistor flanked on both sides by a thermistor
in a bridge configuration. Stuffed it all into the side of a plastic
tube. Air flow differentially heats one thermocouple depending on
direction.
It sorta works, but uses a lot of power (for a battery operated device)
and has a rather long thermal time constant. The thermistors
are tiny, but they're encapsulated in kapton tape. Don't think I can
get 'em out without breaking 'em.
Is there another simple technique I could exploit to infer zero
net pressure differential?
There are cheap differential pressure sensors around that work in this
range.
John- Hide quoted text -
- Show quoted text -
We use a honeywell differential pressure gizmo. I think it sells for ~
$15.
(Newark carries them.)
George H.
Thanks, but the low pressure versions are $72 and digital, so I need a
microprocessor
and a circuit board and power supply and box to put it in and code to run it
and some kind of display....And I've already got that: Omega PCL-200.
I was hoping for a creative option similar in complexity to what I
described.
I've got a UEI EM150. Gonna see what happens when I try to increase
the gain X10.- Hide quoted text -
- Show quoted text -
Hi Mike, Looks like the last time we bought these they came from
digikey. part number 480-2516-ND. (The price has gone up a bit since
the first purchase.) They make different sensitivities. I stuck an
instrument amp across it. I’m not sure how much gain... I could look
up the circuit.
I would guess maybe something like 10V full scale.
George H.- Hide quoted text -
- Show quoted text -
Just plugged one off the self and into a 'scope. 10V = 1 atm.
about 10mV of DC offset, (No attempt made to zero this.) and 2 mV of
crud. The crud is mostly 100MHz stuff that seems to be all over my
lab space. So that could be easily filtered.
George H.
David Eather
Guest
Mon Jan 09, 2012 8:06 pm
On Mon, 09 Jan 2012 16:14:08 +1000, whit3rd <whit3rd_at_gmail.com> wrote:
Quote:
On Saturday, January 7, 2012 2:43:03 PM UTC-8, mike wrote:
I'm building some heat recovery ventilation devices.
Need a way to equalize the internal and external pressure of the house.
Don't need a lot of accuracy, but would like to be able to get close to
zero.
So, you want a manometer that indicates 'positive', 'negative' , and
'near
zero'?
Make a manometer of the diaphragm type, and have the center of the
diaphragm operate a pair of (over-under) switches. To protect
from gusts and surges, just use a narrow tube to 'outdoors' and
let air viscosity work for you.
With a light-colored diaphragm, the switches could operate
on light reflection.
metalized mylar perhaps (a space blanket)?
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