Discussion in 'The Projects Forum' started by witssq, Mar 10, 2011.

  1. witssq

    Thread Starter Active Member

    Mar 29, 2009
    I'm designing high precision pressure sensor signal conditioner.
    And I would like to reduce noise.

    Although many issue about the attached schematic exist, initially noise at between TP7/TP8 and 24PC sensor.

    <Test 1>

    When 3Pin(GND), 1Pin(+10V) is established, then meaure at TP7, TP8 position with 1.5M Shield Cable connected with J3

    Peak to Peak Value

    TP11(+10V) : 50mV
    TP13 : 100mV FIG. 3_13
    TP15, 16 : 100mV FIG. 3_15_1
    TP15, 16 (Opened/Not Connected) :
    65mV Signal Shape is same as FIG. 3_15_1
    TP7,TP8 Peak to Peak : 80mV FIG_3_7, F_3_8
    TP9,TP10 (Opened/Not Connected) : 300mV Signal Shape is same as FIG. 3_7

    <Test 2>

    When 3Pin(GND), 1Pin(+10V) is established, then meaure at 4Pin, 2Pin(Signal) without connection to J3(DIN Connector)

    1Pin(+10V) Peak to Peak : 40mV
    4Pin , 2Pin Peak to Peak : 30mV(Signal Noise size is reduced)

    I found initial power supply ripple 50mV to signal 80mV ripple.
    But Not connected signal ripple is smaller than power ripple.

    Please give me help about how do I reduce this noise.
  2. witssq

    Thread Starter Active Member

    Mar 29, 2009
    I found that FIG_3_15_1 hum ocurrs power on Fluorescent light plugged on common AC multi-outlet receptacle with system. When this lamp is off,
    hum is disapeared.

    Please advise me how I can make not susceptable to this lamp-on

  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    Without spending a fortune for RF interference filters, and experimenting with various forms of copper shielding over the circuit?

    Try putting the project in a metal project box which is attached to earth ground. If the interference is coming in on the AC power lines, you could use an AC power filter module. Neither is a 100% guaranteed cure. Switch to a different light source? or at least put it on a different AC circuit.
  4. Commander#1

    New Member

    Jan 22, 2011
    Yes - shielding, bypassing/decoupling and filtering are going to be your three biggest areas of concern. You might
    even consider fabricating your own Faraday shield using some copper mesh screening material. Those fluorescent
    lights throw hash on the AC lines and into the air. Keep us posted how things are going, please.
    :D Phil Potter :D
  5. t06afre

    AAC Fanatic!

    May 11, 2009
    Your schematic is hard to read. Can you post it as a PDF file? I suspect is other things than the lightning system. Are you able to post a picture of your test setup. It would help. What kind of DAQ eqipment do you use?
  6. witssq

    Thread Starter Active Member

    Mar 29, 2009
    Thanks you.

    Sorry for the late response because of trip.

    One more things I found is that when the lamp is on, on power line of dc output spike noise coninuously not also appears.

    And when air compressor is on, spike noise also appears on DC power line.

    With schematics PDF version and Test Setup Picture is attached.
    Then details for numbering on picture is as follows,
    1) Commercial Power Supply(SMPS +/-15V, 5V triple output)
    2) Multiple outlet receptacle
    1> AC Noise Filter(10) for thos system
    2> Microscopt
    3> Small Air Compressor for making 1.5Kg/Cm2 Air pressure sensor
    4> Flourescent lamp(11)
    5> Soldering Device
    3) AVR 2560 STK purchased.
    4) Power Regulation Board using linear LDO regulator
    5) ADC Board(AD7734)
    6) ADC Board revision circuit
    7) Air pressure sensor signal conditioner
    8) Air pressure sensor enclosure with sensor
    9) Microscope
    10) Commercial AC noise filter
    11) flourescent lamp

    It's (5) ADC Board.

    A commercial AC filter module is already applied, but Frame ground still not applied.

    Of course I would post all proceedings. But what is first thing to do?

    Please let me know procedure to solve this problem.

    Best regards,