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ad7124; In trying to connect and measure voltgae with an precicize Voltgage source I come across a puzzle. I enabled the internal voltage reference and selected this reference in congig0. Measured differential inputs are AIN0 and AIN1. Vbias selected on A

Question asked by jcgeluk on Oct 13, 2017
Latest reply on Nov 6, 2017 by JellenieR

ADC7124 voltage measurement. In applying a precise voltage source on AIN0 and AIN1, I come across a puzzle.

 

ADC settings: AIN0/AIN1 in bipolair mode; VBias set for AIN2 ; Internal reference enabled, Internal reference chosen in CONFIG0.

Wiring: All AIN's have 220 Ohm protection resistor. AIN0/AIN1 connected to floating voltage source. AIN2 (VBias) connected to AIN1. At that point I measure 1.985V.

 

Measurements of -2.5V in steps of 0.5V to +2.5V:

From 0 to +1V and 0 to -1V I see differences between my source of <0.002 V. But at  2 and 2.5 V I see measured voltages of 1.708V and 2.038V. At -2 and -2.5V there are similar large differences?

 

Why is this and what do I have to do to measure over the full range -2.5 to +2.5V?

 

Your answer is appreciated,

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