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ISO 124

Sajeendran B S
Prodigy 20 points
Other Parts Discussed in Thread: ISO124

HI

    I am using an ISO 124 based isolation amplifier in my signal conditioning chain. Just before iso amp there is a differential amplifier whose output is single ended. so effectively one input of iso 124 will be the signal and other( GND 1) will be chassis ground of previous amplifier. The output is connected to PXI based data acquisition system. My doubt is which is the best possible way to connect the shield of the output wire to DAQ...differential or single ended.

The length is 3metres. Two core shielded. What is the min possible peak t0 peak noise obtainable with the iso 124. I am using a sampling rate of 1000.

  • 0
    Guru 21975 points

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    Regarding your ISO124 application, it's difficult to know with certainty but I imagine that a single-ended connection to your data acquisition system should be okay.

    The noise could depend on the nature of your data acq system. It will probably help to limit the bandwidth with a simple R/C filter to 1kHz. The effective noise bandwidth of a simple 1kHz R/C filter is approximately 1.6kHz. Based on the ISO124 spec of 4uV/rt-Hz typical noise:  4uV/rt-Hz  x (1600)^1/2 = 160uVrms.  Peak to peak noise may be about 7-times greater or about 1.1mVp-p. Your input circuitry connected to the ISO124 may contribute more noise.

    These are only approximate calculations and based on typical performance of the ISO124. There can be many possible sources of noise in a complete application setup. Check with an oscilloscope to view the general appearance of any large excess noise as it may be a clue as to its source.

    Regards, Bruce.

     

  • 0 in reply to Bruce Trump
    Prodigy 20 points

    i wanted to know whether there is any problem in connecting the input wire shield to the output wire shield

  • 0 in reply to Sajeendran B S
    Guru 21975 points

    Perhaps I don't understand. It sounds as if you would be connecting the ground on the input side (call it Gnd-1) to the ground on the output side (Gnd-2). If these ground are connected, you have defeated the purpose of the isolation amplifier. Its sole purpose is to allow these grounds to be galvanically isolated.

    The input shield should connect to Gnd-1. The output shield should connect to Gnd-2. The two grounds must not be connected.

    If I have misunderstood your question, please provide a schematic drawing to clarify.

    Regards, Bruce.