Re: Solid State Relays and EMI

From: NeoRenegade (napsterneorenegade_at_hotmail.com)
Date: 07/26/04

  • Next message: Dan Fraser: "Re: Source of SMPS transformers (standard types no custom designs))" 
    Date: Mon, 26 Jul 2004 17:52:37 -0400

    David Harper wrote:

    > I'm using some solid state relays, and having some problems with (I
    > believe) EMI.
    >
    > http://www.cel.com/pdf/datasheets/ps7141a.pdf
    >
    > I'm using this part in the B and C configurations.
    >
    > These items are located near some RF sources operating at about
    > 148MHz. During transmit (.5W power), I'm getting some false "on"
    > states. I'm pretty sure this isn't due to the equipment on the load
    > side, as removal of the SSR's eliminates the effect.
    >
    > 1. Anyone know if these type of SSRs are subject to EMI that can
    > cause false on-states?
    > 2. Would induced AC voltages (from the RF source) in the load lines
    > (around 148MHZ) decrease the R-off resistance?
    > 3. If the problem is in the SSR's, anyone have any suggestions
    > regarding how to lessen/prevent this? (EMI shielding, other PN's that
    > are immune to this, inductors/caps that could be placed in the load
    > lines, etc).
    >
    > Thanks for your time!
    > Dave Harper

    1. It's very likely. In my classes, I've been taught that EMI can bugger
    up the proper working of just about any circuit, so it should always be
    taken into consideration.
    2. Er, I think it's a simple matter of induced current in the line
    giving false hi signals.
    3. First thing I'd do is make absolutely sure your relay coil is
    grounded rather than floating when in the "off" state. Being assured of
    that, if the problem persists, you might want to try a simple RC
    band-elimination filter. If you do not have it handy, I can give you the
    formula to determine the R and C values.

    I apologize in advance if your electronics knowledge is more advanced
    than mine and I've just wasted your time.

    - NR

  • Next message: Dan Fraser: "Re: Source of SMPS transformers (standard types no custom designs))"