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I've attached a diagram of what I'm talking about.

I have a large (600x300x10 mm) aluminum block in which I place thermistors to monitor the temperature distribution in the plate (in a standard voltage divider circuit.)

When I have done this before, I have simply wired two leads to each thermistor (one ground, one voltage line) and passed them out of the plate to my PCB. I am now looking at a lot more sesnors (maybe up to 100) and that makes for a lot of wire management, not to mention expensive components like 200-way ribbon cable.

I thought I could half the soldering and number of wires if I ground the aluminum (connect it to GRD of my Arduino) and solder the thermistor ground lead to the aluminum body.

However, this plate will change temperature quite a bit (say, in the range of 60 to -10 C) and I don't know if this makes for a good GND. I'm worried that a plate this large, that changes temperature over an extensive range, would somehow change the GND and make for unreliable and innacurate sensor readings. I certainly don't want the sensors accuracy or reliability to be dependent on plate temperature because the level of my ground is changing.

Am I overthinking this or, to get good and accurate sensor readings, will this plan not work?

diagram of what I'm wanting to try

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    \$\begingroup\$ Have you ever tried soldering to an aluminum block? \$\endgroup\$
    – John D
    May 19, 2022 at 22:39
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    \$\begingroup\$ You can design SMD signal diodes on FPC strips with 3M thermal tape instead of thermistors then use analog Mux to an INA differential amp to reduce EMI with a 1mA and use the diode thermometer approach with gain to measure temp. \$\endgroup\$ May 19, 2022 at 23:28
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    \$\begingroup\$ Maybe a thermal camera is a viable solution? \$\endgroup\$
    – Kartman
    May 20, 2022 at 1:49
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    \$\begingroup\$ Trust me, soldering to aluminum is far more difficult than soldering two copper joints, even if the aluminum isn't a large heatsink. You need really aggressive flux and specially formulated (read: expensive) solders and even then it's a pain. (Incidentally, it's GND for ground, not GRD--that would be for a signal guard.) \$\endgroup\$
    – Hearth
    May 20, 2022 at 4:04
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    \$\begingroup\$ Building on Tony's suggestion, have you considered making a PCB with a bunch of board mount sensors on one side, the microcontroller on the other and then mounting it with thermal adhesive or paste to the block? Much easier to read out 100+ channels if you keep everything on board and just have a USB port out the back. Could even use digital sensors and avoid analog entirely. \$\endgroup\$ May 20, 2022 at 13:58

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You can design SMD signal diodes on FPC strips with 3M thermal tape instead of thermistors then use analog Mux to an INA differential amp to reduce EMI with a 0.1 mA and use the diode thermometer approach with gain to measure temp.

The 1mA current source would be common on the Mux output side , which makes this a simple stick on and interface with 1kHz sample rate and get 10 samples/s for 100 sensors.

There are also the TI linear temp sensors that are fixed mV/'C but you need a negative supply for temperatures below 0'C.

Make it look as easy as sticking on an LED STRIPLED but with all the IO diodes shared thru a 100:1 analog mux common ADC port. Your noise needs to be below 2mV for 1'C accuracy and can be LP filtered with a Nyquist filter , oversampled and decimated for averaging if needed.

You can solder to aluminum if you have the right torch and flux, but that would/could be a mess. I've seen researchers gold plate Alum blocks for Spectrum Analyzers so that it was easy to solder coax to it. But that seems likeoverkill https://superiorflux.com/papers/TWJ.May.2018.Tech.Solder.Al.pdf

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