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Do accelerometers drift?

Discussion in 'Electronic Design' started by Jim Thompson, Jul 24, 2003.

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  1. Jim Thompson

    Jim Thompson Guest

    Even government grade accelerometers drift... it's the nature of the
    beast. Most control systems augment the accelerometer with GPS or
    other locating devices. The accelerometer is only of short term,
    fill-in-the-data-points, value.

    ...Jim Thompson
     
  2. H.J.

    H.J. Guest

    I'd like to build a 3 axis tilt sensor.

    I would like to know if low-cost, hobby-caliber, solid-state accelerometers
    drift. If you set one on a table do they register +1g all day long
    consistently?

    Does temperature affect them?
     
  3. Rob

    Rob Guest


    Hello HJ, I can't offer a reply to your question, but I am interested in
    finding a source of low cost accelerometers - if you don't mind, I would be
    interested in finding out what you are using and who manufactures them.
    Others are most welcome to reply / comment as well. Thanks

    Regards
    Rob
     
  4. Glen Walpert

    Glen Walpert Guest

    True enough, but he was asking about tilt sensing which is a bit less
    demanding than inertial navigation. While low cost MEMs
    accelerometers of the sort used in every airbag recentlly manufactured
    do have high thermal drift, high unit to unit variation, and not the
    best shock resistance, they are suitable for use in low to moderate
    accuracy tilt sensors, and once calibrated they will "register" +1g
    all day long. Perhaps not +1.000g all day long, unless you are using
    one of the better MEMS accelerometers like the ADXL105 with good
    filtering, individual calibration and temperature compensation, and a
    fairly stable environment.

    Unless the OP wants high accuracy (in which case he should look at
    electrolytic tilt sensors) he should give it a try. The mfgrs app
    notes on tilt sensing are honest about the accuracies which can be
    achieved, suggest you read them.

    BTW I once dissasembled an inertial navigation accelerometer made in
    the days before GPS, which used force balance inside a constant
    temperature oven, very clever mechanism but obviously very expensive
    too.

    Glen
     
  5. Leon Heller

    Leon Heller Guest

    I've used the ADXL202 (Analog Devices). They work OK, and you can get free
    samples.

    Leon
     

  6. ADXL105 is a piece of junk in terms of accuracy and stability, as well
    as other accelerometers of AD. It is really sensitive to mechanical or
    thermal shock also.
    The best you can get from it is about 0.05g accuracy.

    VTI Hamlin does better MEMS accelerometers, though you will not get any
    better "true" accuracy then 0.01g.
    Electrolytic sensors are very gentle. They can't take heat, cold, or
    vibration.


    Vladimir Vassilevsky, Ph.D.

    DSP and Mixed Signal Design Consultant

    http://www.abvolt.com
     
  7. H.J.

    H.J. Guest

    So if Accelerometers do drift, what do they drift to?

    If one at rest initially registers +1g, does it drift to +4g after an hour?
    and then go to -6g four hours later? i.e. it drifts in some random range

    or

    does it start at +1.000 g and then slowly tick up to it's max g limit after
    some long period of time?

    or ... what else?
     
  8. onestone

    onestone Guest

    Crap. It isn't exactly rocket science to insulate them from both sudden
    thermal changes or sudden shock, and long term monitoring shows that
    handled correctly their stability is fine.
     
  9. MEMS accelerometers exibit large zero drift. The gain remains pretty
    stable though.
    Zero drift is quite random and very different from unit to unit.
    The other problem with MEMS is the mechanical hysteresis.

    Vladimir Vassilevsky, Ph.D.

    DSP and Mixed Signal Design Consultant

    http://www.abvolt.com
     
  10. Why didn't you tell me any numbers? Nothing to say?
    Have you ever tried MEMS other then AD?
    FYI, ADXLs are the sloppiest sensors ever.


    Vladimir Vassilevsky, Ph.D.

    DSP and Mixed Signal Design Consultant

    http://www.abvolt.com
     
  11. onestone

    onestone Guest

    What, numbers to match those you supplied? Jeez, what a prune. And yes,
    I've been using ADXL's since 1990/1 before they were commercially
    available. I've also used several other types of accelerometer, and a
    variety of other MEMs devices. I've been involved with micromachined
    products since the mid 80's, both in development and as a user.

    FYI your opinion only, don't blame the tools.

    Al
     
  12. netsurfr

    netsurfr Guest

    If you're looking for a good 3-axis accelerometer packaged as a
    standalone IC, try the Measurement Specialists ACH-04-08-05. It
    measures in all 3 axis of movement. The 3 circuits operate
    independently and look like JFETs. A typical circuit is shown on the
    data sheet.

    I've been working on circuits that interface to MEMS accelerometers
    (and other sensors) for a while, and this one has good specs. I don't
    know about price though. This one might be expensive. I recommend you
    call them at 610-650-1500 and get a quote. I attached the drawing in
    case you want to look it over first. Their web site is at
    http://www.msiusa.com

    netsurfr
     
  13. netsurfr

    netsurfr Guest

    If you're looking for a good 3-axis accelerometer packaged as a
    standalone IC, try the Measurement Specialists ACH-04-08-05. It
    measures in all 3 axis of movement. The 3 circuits operate
    independently and look like JFETs. A typical circuit is shown on the
    data sheet.

    I've been working on circuits that interface to MEMS accelerometers
    (and other sensors) for a while, and this one has good specs. I don't
    know about price though. This one might be expensive. I recommend you
    call them at 610-650-1500 and get a quote. I would attached the
    drawing but this newsgroup does not allow binaries. The web site is
    at http://www.msiusa.com

    netsurfr
     
  14. onestone

    onestone Guest

    They were around the same price as ADXL202's, but are much higher ranged.

    Al
     
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