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I am designing a circuit that needs to have 18 thermistors to measure the temperature at various points. The thermistors are 2metres+ away from the ADC

Usually when I power a thermistors I use a Vref IC and an opamp buffer. I also take the op-amp buffer into the ADC ref for ratiometric measurement. With 18 Thermistors and 2-3mA per thermistor, that's getting up to 50mA+ and beyond the current output of op-amp buffers.

How should I do this many thermistors in parallel? Should I split them up into say 3 blocks of 6, with 3 six channel ADCs and have 3 op-amp buffers from the Vref?

Or should I do all 18 at once with 1 op-amp buffer

Should I even be using an opamp buffer?

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  • \$\begingroup\$ You don't like DS18B20? \$\endgroup\$
    – bobflux
    Mar 18, 2021 at 23:23
  • \$\begingroup\$ The question only makes sense if you talk about the resistance of the thermistor over the temp range of interest, and what sort of precision you need. \$\endgroup\$
    – Scott Seidman
    Mar 18, 2021 at 23:23
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    \$\begingroup\$ Are you trying to get average temperature over some area? \$\endgroup\$
    – user263983
    Mar 19, 2021 at 0:43
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    \$\begingroup\$ Ah if you are connecting 18 devices in parallel, then the host is crowded with wires. Lazy guys usually do it in serial, or daisy chain. The DS18B20 suggest by @bobflux is a 1WIRE interface/protocol, which uses only one wire in daisy chain. I once linked 15 DS18B20 and did not find any problem. DS18B20 Temperature Sensor - Rpi 3/4 Driver, Wiring, Detection, and Python Programming Asked 1 year, 8 months ago Active 2 months ago Viewed 1k times raspberrypi.stackexchange.com/questions/100203/… \$\endgroup\$
    – tlfong01
    Mar 19, 2021 at 1:20
  • \$\begingroup\$ Why not add more buffers in parallel link? \$\endgroup\$
    – Ernesto
    Mar 19, 2021 at 4:20

1 Answer 1

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Is the ADC time-multiplexed?

If so then time multiplex the feed excitation to the thermistors as well.

In sequence apply excitation to the specific thermistor, wait a bit, measure the thermistor with the ADC then move to the next one.

This would also have the advantage of reducing the power dissipation in the thermistor to minimize the error due to self-heating.

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