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

Discussion in 'Embedded' started by Roberto Hawkowski, Nov 22, 2003.

  1. 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
     
    Roberto Hawkowski, Nov 22, 2003
    #1
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  2. Roberto Hawkowski

    Mark Little Guest

    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
     
    Mark Little, Nov 22, 2003
    #2
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  3. 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.
     
    Roberto Hawkowski, Nov 22, 2003
    #3
  4. 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.
     
    John R. Strohm, Nov 22, 2003
    #4
  5. Roberto Hawkowski

    ZForce Guest

    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.
     
    ZForce, Nov 22, 2003
    #5
  6. <3fbfaf0c$0$1721$>) about 'Air flow and
    vacuum/pressure sensors in a dust collection system', on Sun, 23 Nov
    2003:
    Manometers. I suppose they are called personometers now.
     
    John Woodgate, Nov 22, 2003
    #6
  7. Thank you for reply. I think the biggest problem on measuring the pressure
    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...
     
    Lewin A.R.W. Edwards, Nov 23, 2003
    #7
  8. Roberto Hawkowski

    Richard Guest

    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
     
    Richard, Nov 23, 2003
    #8
  9. Roberto Hawkowski

    Jim Adney Guest

    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, Nov 23, 2003
    #9
  10. Roberto Hawkowski

    Jim Adney Guest

    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.

    -
     
    Jim Adney, Nov 23, 2003
    #10
  11. Roberto Hawkowski

    Bushy Guest

    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
     
    Bushy, Nov 25, 2003
    #11
  12. 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

    To send private email:

    where
    "0_0_0_0_" = "martineu"
     
    Martin Euredjian, Nov 25, 2003
    #12
  13. 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.
     
    Roberto Hawkowski, Nov 27, 2003
    #13
  14. Roberto Hawkowski

    Jim Stewart Guest

    Save yourself a lot of time and money and use a
    motor with an offset flywheel instead.
     
    Jim Stewart, Nov 27, 2003
    #14
  15. 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.
     
    John R. Strohm, Nov 27, 2003
    #15
  16. Roberto Hawkowski

    N. Thornton Guest

    I cant see this achieving much. Youve still got all the dust on it, it
    will probably reblock, often quickly.

    Regards, NT
     
    N. Thornton, Nov 27, 2003
    #16
  17. Roberto Hawkowski

    Rich Grise Guest

    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
     
    Rich Grise, Nov 27, 2003
    #17
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