Air flow and vacuum/pressure sensors in a dust collection system

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Hello Everybody,

In an industrial application I need to monitor air flow and pressure/vacuum
in a dust collection system (it is just like a huge vacuum cleaner) to
understand if the filters are working okay or not.

Would any one have any experience in such an application to share or any
suggestion for this type of application?

Thank you.

Roberto Hawkowski
nospam snipped-for-privacy@hotmail.com





Re: Air flow and vacuum/pressure sensors in a dust collection system

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pressure/vacuum
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You can use a differential pressure gauge across the filters. This should
give you an indication if they are getting clogged - the higher the pressure
differntial, the greater the blockage in the filter. This can be inaccurate
if the filter material can tear as it reduces the pressure differential and
gives a false reading. Air flow can also be measured using differential
pressure, or by using an axial turbine generator.It is also possible to use
a hot wire velocity sensor where the cooling is proportional to the air
flow.


Mark



Re: Air flow and vacuum/pressure sensors in a dust collection system
Dear Mark,
Thank you for reply. I think the biggest problem on measuring the pressure
is the dust in the environment. Would you have any suggestion for which type
of sensor I can use as differential pressure gauge in dusty environment ?

Thx.


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pressure
inaccurate
and
use



Re: Air flow and vacuum/pressure sensors in a dust collection system
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It really depends on the pressure and vacuum levels you expect to see.

Pull down an automotive sensor catalog.  There are probably several hundred
different types of pressure and vacuum switches and sensors used in automobile
engines.  See if you can find something that matches up.



Re: Air flow and vacuum/pressure sensors in a dust collection system
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Should it really make much difference? There will be practically no
air flow through the hoses leading to this sensor, unless the filter
fails. If you have a hood with the open end facing downstream, to
create a "dust shadow" around the test point tap, and the operator who
replaces the filter is trained to blow out dust from the test point as
part of the process, it should surely be OK for a long time?

What is the nature of the dust? (Is it sticky, corrosive, abrasive,
highly reactive, etc?)

Another approach to this problem is to cut two portholes in the pipe,
one before the filter and one after, and use a tough rubber diaphragm
with a strain gauge to measure approximate absolute pressure.

You can also infer the state of the filter by looking at the *output*
flow rate from the fan that's creating this partial vacuum. The
apparatus to do this can be nothing more complex than a swinging lid
over the output pipe, and a light gate...

Re: Air flow and vacuum/pressure sensors in a dust collection system
On Sun, 23 Nov 2003 02:03:11 +1100 "Roberto Hawkowski"

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The standard differential pressure gauge used to monitor overspray
filters in paint booths is just an oil-filled manometer. I don't
remember the differential pressure range they work in, but they can't
be too expensive.

Gauges like this usually aren't bothered by dusty air because there is
virtually no airflow in thru either of the sensor openings.

-
-----------------------------------------------
    Jim Adney             snipped-for-privacy@vwtype3.org
           Madison, WI 53711 USA
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Re: Air flow and vacuum/pressure sensors in a dust collection system

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pressure/vacuum
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Does it have to be electronic? I cant remember the name of them, but they
are a bit of clear plastic tube filled with green water in a U shape, and a
scale behind, maybe 2 of them can be used to measure the pressure
differential, low tech solution but they aren't going to clog up with dust
to quickly.




Re: Air flow and vacuum/pressure sensors in a dust collection system
vacuum/pressure sensors in a dust collection system', on Sun, 23 Nov
2003:
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Manometers. I suppose they are called personometers now.
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Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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Re: Air flow and vacuum/pressure sensors in a dust collection system

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The word is manometer. You make them differential by hooking one end
of the U-tube to the passage on each side of the filter.

The differential pressure is then proportional to the difference in
height of the working fluid on the 2 sides of the U-tube.

-
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    Jim Adney             snipped-for-privacy@vwtype3.org
           Madison, WI 53711 USA
-----------------------------------------------

Re: Air flow and vacuum/pressure sensors in a dust collection system
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Here's a vague pointer...

My central heating system (gas), uses a simple vacuum switch to sense
pressure differential from the exhaust fan's input vs. output (to decide
if the exhaust fan is actually functioning).

In effect, it's a switch that changes state when there's a pressure
differential.  Very simple and effective if you're only looking for
good/bad state (not pressure readings).  I'd expect the differential
could be tuned in some models to determine the threshold for a "clogged
filter".

Regards,
Richard

Re: Air flow and vacuum/pressure sensors in a dust collection system
One machine I worked on had a flow sensor made from a piece of tin plate
about one inch square attached to a microswitch arm that sat in the air flow
near the fan. when the fan was on and air flowing it made the plate move and
operate the switch.

Changing the size of the plate would change the ari flow required to operate
the switch. Gravity balanced this unit but a spring might be just as
effective. Have a look at the dust indicator that is fitted to several
models of vacuum cleaners and maybe add a magnet and a reed (relay) switch
to operate an idiot light.

Hope this helps,
Peter



Re: Air flow and vacuum/pressure sensors in a dust collection system

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pressure/vacuum
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Are you talking about a dust collector for a woodworking shop or similar
application?

How many CFM's does the fan move?

What's the nature of the dust (hard, soft, wet, dry, dangerous, harmless,
etc.)?

What degree of accuracy do you need?

What's the ultimate purpose of the pressure measurement?  For example, do
you just want to trigger an alarm to have an operator change the filter?

There are problably over a dozen ways you can measure airflow.  From
shed-vortex sensors to simple linear plungers in the airstream.  To narrow
this down to a small set suitable for your application you have to specify
the constraints/application with a bit more detail.

Example 1: A typical home/industrial air conditioner filter will bend as it
clogs.  You could place a plunger touching the back of the filter to measure
this deflection.  The firmware could auto-calibrate and "learn" about what a
good filter looks like and trigger an alarm when the filter is clogged.

Example 2: Use a radial impeller in the airflow.  All air must pass through
it, and, in order to do this, the impeller will/must rotate.  Debris will
not affect it if designed properly.  Generating some sort of a proportional
airflow number is pretty simple.

Example 3: A piece of piezoelectric film sandwiched between two metal
plates.  Arrange this perpendicularly to the airflow and mounted with
brackets such that the plate is in the center of the air stream.  This is
located prior to any air filtration.  Larger debris will impact the plate
and generate voltage pulses.  Flow/no-flow determination is very simple.
With more knowledge of the material being vacuumed it might be possible to
generate coarse velocity/volume data as well.

Example 4: Bond a heating element and a thermistor to a common piece of
metal (maybe inside a sealed tube).  Insert this into the duct.  With no
airflow the heater will stabilize at a certain temperature.  As air flows,
it will be cooled.  Measure with the thermistor.

Like I said, there are so many ways to do it...


--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Martin Euredjian

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Re: Electromagnetic actuator to shake the filter
Thank you all for your inputs.
As I mentioned in the original posting, I'll try to control a dust
collection system.
One of the major problem was detecting the air flow and/or
vacuum/pressure/depresion in the system. Now assumed that we solved this
detectin problem. The next step is shakeing the blocked filter. I think an
electromagnet would do the job. What I need to have is an electomagnetic
actuator that can shake (translate 25kg filter over 20cm with 2-5Hz.) the
filter.

My questions are related to design/calculations of electromagnetic actuator.
Assume that I will  use 240v AC line voltage.
(1) How to calculate number of turns to have 25kg pulling or pushing force?
(2) Diameter of the wire to be used in the actuator coild?
(3) Diameter of the coil ?

Thx.



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pressure/vacuum
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Re: Electromagnetic actuator to shake the filter
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Save yourself a lot of time and money and use a
motor with an offset flywheel instead.


Re: Electromagnetic actuator to shake the filter

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Don't even try to do the electromagnetic thing.

Use a geared-down motor and a crank drive.

An electromagnet will give you a rectangle-shaped shake waveform, and probably
tear your filter to pieces.  A motor will give you a sinusoidal shake.



Re: Electromagnetic actuator to shake the filter
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I cant see this achieving much. Youve still got all the dust on it, it
will probably reblock, often quickly.

Regards, NT

Re: Electromagnetic actuator to shake the filter
Rather than trying to shake a huge thing like that, how about
just raising it a few inches and dropping it? Kinda like when
you whap the coffee filter basket against your hand to dump
out the grounds.

CHeers!
Rich

Roberto Hawkowski wrote:
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