Measure resistance with ADC

[funghome]

adc measure resistance

I want to measure an unknown resistor resistance with ADC, and calculate the unknown value using below circuit.
But I don't know how to calcualate the value.
LTC2410 is a 24 bits adc.
If 820000 was read, what is the resistance?

 

[laktronics]

how to measure resistance adc

Hi,

You can calculate the resistance R in K ohms as follows:

REFadc = VREF+ - VREF-
= Vcc - Vcc (10 + R )/ (20 + R)
= Vcc [ 1- (10+R)/(20+R)]
= Vcc [ (20+R-10-R)/(20+R)]
= Vcc [ 10/(20+R)]
Analog Input = Vcc * R/(20+R) = REFadc* (ADC Reading / ADC Full Scale)
So,
Vcc*R/(20+R) = Vcc[10/(20+R)] * 8,20,000 / 2^24

R = 10 * 8,20,000 / 2^24
= 0.48876 K ohms
= 488.76 ohms


Regards,
Laktronics