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Struggling to select the correct Analog Switch

BigG

I wish to create this circuit (not a fully complete design), where I am hijacking a Pt100 sensor for my own readings while still allowing an existing system to read the values correctly. I'm thinking that if I switch fast enough, with the help of smoothing capacitors, I could just about get away with it as there will be a fair bit of sampling and averaging to get a temperature value.

To do this, I decided to use an analog switch as these typically have low on resistance values. What I cannot figure out is whether I need a device like a Vishay DG419LEDY-T1-GE4 which has a signal range of -15V to 15V or I could use a SPDT analog switch with a lower voltage. I think I am correct in thinking that the max voltage of Vin is the max voltage allowed through the COM-NC pin etc.

I just wanted confirmation.

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Of course, if there is an easier way to do this, I love to hear your views as I have a habit of over complication.

Thanks

Colin

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  • 0

    Hi Colin,

    If there was absolutely no other way (i.e. depends on your use-case/end requirement/connected equipment as Michael says), and you definitely had to read that same PT100, directly at the sensor, then if it were me, I'd probably experiment with a single SPDT reed relay (only needs one, if you've not got any common connections between your system and the existing system), but some systems might check for broken sensor connections, or have other issues with the connection being removed by your microcontroller periodically. Reed relay has current consumption, but still very low overall if (say) the temperature is only being measured (say) once a minute.

  • 0 in reply to shabaz

    Yes needs to be the same Pt100 as cannot insert another sensor in same location. Yes, you are right a single SPDT is probably all I need. Thanks Shabaz for the suggestion to use a reed relay. I will do some research.

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