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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.

image

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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    I was reflecting on the comments made to my half-baked solution. Very enlightening and very helpful. Thanks.

    I do recall seeing a digital voltmeter solution using an Arduino and thought, why no incorporate that. So this is what I came up with (hopefully this a 3/4 baked solution). Haven't shown in diagram but assuming MCU GND can be attached to VSS (system ground) in Control Panel.

    Still not sure if it helps me determine the pt100 resistance value and thus the temperature and whether this new circuit will impact the control panels existing readings. Maybe I need different resistor values etc.

    I'm also assuming Analog Read probably needs opamp as per  comment. Also assuming Analog switch can be swapped out for a different SPDT like a reed or solid state relay as on resistance is no longer a factor.

    image

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  • 0

    I was reflecting on the comments made to my half-baked solution. Very enlightening and very helpful. Thanks.

    I do recall seeing a digital voltmeter solution using an Arduino and thought, why no incorporate that. So this is what I came up with (hopefully this a 3/4 baked solution). Haven't shown in diagram but assuming MCU GND can be attached to VSS (system ground) in Control Panel.

    Still not sure if it helps me determine the pt100 resistance value and thus the temperature and whether this new circuit will impact the control panels existing readings. Maybe I need different resistor values etc.

    I'm also assuming Analog Read probably needs opamp as per  comment. Also assuming Analog switch can be swapped out for a different SPDT like a reed or solid state relay as on resistance is no longer a factor.

    image

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