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I am building a setup to measure various parameters across a temperature range from -55°C to +125°C. The devices under test will be placed in a climate chamber. There are around 10 signals from each DUT to be measured by equipment outside the chamber. The sampling rate is fairly relaxed (many seconds). Measurements are DC (so no high speed signal issues). Switched voltages are below 12V.

I plan to have around 50 DUTs in the chamber. Only one DUT has to be connected to the measurement equipment at a time.

I wonder what is an efficient and reliable way to mux ~500 signal to and from a climate chamber?

Some solutions that I considered:

  1. Switching signals outside the chamber - physically impossible, 500 wires will not fit through the conduit (and it would be a mess of wires...).

  2. Switching inside the chamber using ordinary relays - may not be reliable

  3. Switching inside the chamber using relays rated for such environment - horribly expensive

  4. Switching inside the chamber using solid state devices - may have unpredictable effect on the measured signals

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    \$\begingroup\$ What about reed relays? \$\endgroup\$ – DKNguyen Oct 19 at 19:42
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    \$\begingroup\$ 50 DUTs is a lot for climate chamber testing (part of DVT -- design verification testing). Why so many? \$\endgroup\$ – Dave Tweed Oct 19 at 20:48
  • \$\begingroup\$ Reed relays are perfectly fine if they can operate in such temperatures. \$\endgroup\$ – filo Oct 20 at 8:16
  • \$\begingroup\$ I'd consider building up five rotary switches, probably. Something that has 11 positions like this. But I'd lengthen the shaft to add a full 10 poles. The knob on the outside, wafer stack inside. The 11th position would be unconnected and only one of the five such switch stacks I built would be allowed to select a DUT. Simple wiring. I'm not suggesting you do this, as it takes time and that's money. But perhaps it suggests other ideas to pursue. \$\endgroup\$ – jonk Oct 20 at 10:45
  • \$\begingroup\$ You might find this interesting: m.littelfuse.com/~/media/electronics/application_notes/… \$\endgroup\$ – DKNguyen Oct 21 at 20:19
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I would try to use an analog mux with low on resistance such as the adg1606. https://www.analog.com/en/products/adg1606.html

It has less than 8ohms resistance over most of your temperature range and likely won't have a problem in cold where the mux performance isn't specified.

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You have many options:

  1. Relay is the best option for instrumentation.

  2. Sometimes you can Solder the wire to another, some temperature sensor has this feature, then you have the whole room temperature instead of one instrument. (many resistance sensors have this feature, for example in Wheatstone bridge)

  3. Selecting a digital output sensor may help to multiplex (for example PWM output sensor)

  4. In some cases, you can switch the power of sensors on or off instead of signal.

  5. If your signal amplitude is not very low and the analog multiplexer noise is neglected you can use analog multiplexer IC. (In a startup, consider the maximum current that a long wire needs.)

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