I'm getting quiet a large discrepancy between my measured error and predicted errors, with my measured being significantly lower then predicted. The error values in the table should be RTI, described from application note AN539. I am using the AD8422ARZ IN-amp
My gain is set to ~100x, with a 200Ω 1% 100ppm resistor (I'm going change this to a better one), and I'm measuring a load cell excited with 5V and has a full scale output of 15mV
I've measured the output of the AD8422 with a Keithley 6.5digit multimeter, and was getting ~20.83uV of drift (output), Assuming I'm getting the x100 gain I expect, that would be ~208.3nV with respect to the input. I'm also measuring the temperature on the board and it not increasing much beyond ~0.3C, I'm getting this values from the temperature output of the VREF IC REF5025
If I'm doing my calculation correctly I have ~69.6ppm of drift error which I believe that mean I can expect ~70ppm of my full scale input voltage in drift, which is (70/1E6)*0.015 = 1.05E-6V , this is significantly higher that what I'm measuring, what am I missing?
I'm less worried about my accuracy as I can calibrate that out, the drift and noise are my main concerns. The data plots were taken over the course of 5 min at a sample rate of 1SPS.
Amplifier output (After 200Hz Low lass)
Circuit
Error Table
| -- | AD8422ARZ | AD8422BRZ | -- | AD8422ARZ | AD8422BRZ | |
| Absolute Accuracy | -- | -- | ||||
| Input Offset Voltage | -- | 60 | 25uV | -- | 4000.0 | 1666.7ppm |
| Output Offset Voltage | -- | 300 | 150uV | -- | 20000.0 | 10000.0 |
| Input Offset Current | -- | 0.3 | 0.15nA | -- | 6.6 | 3.3 |
| Common Mode Rejection | -- | 126 | 134dB | -- | 83.5 | 33.3ppm |
| Gain | -- | 0.2 | 0.04% | -- | 2000.0 | 400.0ppm |
| Resistor | -- | 1 | 1% | -- | 10000.0 | 10000.0ppm |
| -- | Total | -- | 36190.1 | 22203.2ppm | ||
| -- | -- | -- | -- | -- | -- | -- |
| Drift from 30 to 30.3 | -- | -- | ||||
| Gain Drift | -- | -80 | -80ppm | -- | 24 | 24ppm |
| Resistor Drift | -- | 100 | 100ppm | -- | 30 | 30ppm |
| Input Offset Voltage | -- | 0.4 | 0.3uV/C | -- | 8 | 6ppm |
| Input Offset Current | -- | 1 | 1nA/C | -- | 6.6 | 6.6ppm |
| Output Offset Voltage | -- | 5 | 2uV/C | -- | 1 | 0.4ppm |
| -- | Total | -- | 69.6 | 67.0 | ||
| -- | -- | -- | -- | -- | -- | -- |
| Resolution | -- | -- | ||||
| Gain Non Linearity | -- | 10 | 10ppm/FS | -- | 10 | 10 |
| Typ 0.1 Hz–10 Hz Voltage Noise, uV p-p | -- | 0.15 | 0.15uVpp | -- | 20 | 20 |
| -- | Total | -- | 20.0 | 20.0 |
--VRef
Formatted the table
[edited by: SCLP at 9:20 PM (GMT -4) on 25 Jul 2024]
