# optimal Voltage dividers for measuring ec/thermistor

I'm trying to find the optimal, or at least a good resistor to put into a voltage divider to measure a thermistor, and an electro-conductivity K10 probe. The range is 10 uS/cm to 1 S/cm, and an operating temperature of 0-70 Celsius.

So equations gave me a working resistance of ~80 ohms to 19M ohms. I'm thinking that given the range of resistance it might be difficult to have a single resistor to compensate.

Also I'm using a 1k thermistor, and was wondering if in that case a 1k would be the optimal resistor to pair with that as well?

____/\/\/\_____thermistor____ |||gnd
|     ?     |    probe
(5v dc)   mcu


I've played around; seems a 10k is more accurate in getting the value of the thermistor.

So if I have known solutions, and a known probe the resistance should be in theory known. A K 10 probe and a .15 S solution should come out w/ 1.5 ohm?, or would it be ohm/cm?

• Can you please add a schematic to show which resistor you mean? – auoa Jan 31 '17 at 19:50
• For that conductivity range, no single-scale metering is likely to prove satisfactory. You'll need to break it up into multiple ranges, or use a logarithmic converter. – Whit3rd Jan 31 '17 at 22:28