Attenuation of ±100V

Discussion in 'The Projects Forum' started by raj1391982, Oct 10, 2007.

  1. raj1391982

    Thread Starter New Member

    Dec 20, 2006
    4
    0
    Hello sir,
    I am working on a project, making Data Acquisition System in which the signal from sensor is having strength of ±100V with current in mA. Along with this I have to provide isolation of 1.1KV, filter and drive up to 10 meter through cable….
    Options that I have thought of are:
    1. Attenuation: attenuate using ultra precession resistors network.
    • Will this work? :confused:
    • But what should be criteria in selecting resistors? And specifications?

    Please suggest me something to kick-start my project on to the first step….
    Thanx….. :)
     
  2. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    I can give you a more detailed answer later (I am at work). You could very well use precision resistors. Off the top of my head I would suggest 0.01% tolerance or better. This alone will not provide isolation. You could use a difference amplifier that can withstand high common-mode voltages with an isolation amplifier downstream.
     
  3. raj1391982

    Thread Starter New Member

    Dec 20, 2006
    4
    0
    ok sir.....
    please be back to me for suggestions.....
    i m going to use isolation amplifier of 1.5KVrms from Bur Brown or Maxim.....
    and for attenuation i m going to use L-network or T-network of resistors with resistors in range of few 100s of ohms so as to avoid frequency factor in circuit... (bandwidth of signal is 50KHz).... is it ok.... ?
    Thanx....
     
  4. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    I say to use a monolithic difference amplifier from Texas Instruments or Analog Devices. The INA117, INA118, or the AD629 are examples, and they can withstand common-mode voltages beyond +/-100V.
    These will provide high common-mode rejection, and the internal resistors will not only be matched for that purpose, but will also track over temperature since they are on the die.
    You then could take the output from the difference amplifier into a second stage that utilizes an isolation amplifier like the ISO124 or something similar. Your next problem will be providing an isolated power solution. I am not that familar with power solutions, but I would look for a DC/DC isolated converter from Texas Instruments or National Semiconductor.
     
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