# Large ADC sampling error on rt\_box2 – ~8 deviation from true constant value

**URL:** <https://forum.plexim.com/t/large-adc-sampling-error-on-rt-box2-8-deviation-from-true-constant-value/3116>\
**Category:** RT Box\
**Tags:** c2000\
**Created:** [May 28, 2026, 1:47pm UTC](https://forum.plexim.com/t/large-adc-sampling-error-on-rt-box2-8-deviation-from-true-constant-value/3116 "2026-05-28T13:47:21Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![yanyinyan](https://avatars.discourse-cdn.com/v4/letter/y/779978/32.png) [@yanyinyan](https://forum.plexim.com/u/yanyinyan)\
**Post date:** [May 28, 2026, 1:47pm UTC](https://forum.plexim.com/t/large-adc-sampling-error-on-rt-box2-8-deviation-from-true-constant-value/3116/1 "2026-05-28T13:47:21Z")

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I’m currently using the rt\_box2 and facing an accuracy issue with ADC sampling.

In my model:

The **plant** block uses constant parameters, all set to **90**.

In the **controller** block, I use an ADC sampling module to read these values.

The problem is that the actual sampled values deviate from the true value by about **8** (i.e., the error is roughly 8). The true value is 90, but the sampled result is around 82.

Has anyone encountered similar ADC inaccuracy on rt\_box2? Could this be a configuration issue, driver problem, or hardware limitation? Any suggestions to improve sampling accuracy would be greatly appreciated.

Thank you.

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**Author:** ![Munadir\_Ahmed](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/munadir_ahmed/32/1540_2.png) [@Munadir\_Ahmed](https://forum.plexim.com/u/Munadir_Ahmed)\
**Post date:** [May 28, 2026, 2:09pm UTC](https://forum.plexim.com/t/large-adc-sampling-error-on-rt-box2-8-deviation-from-true-constant-value/3116/2 "2026-05-28T14:09:07Z")

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Hi yanyinyan,

It is difficult to debug the issue without a model. A couple of questions that would help narrow this down:

- What scale factor are you using to output the constant value of `90` through the Analog Output block and what is the Analog Output Voltage Range you are using?

- With the selected scale factor, when you measure the Analog Output voltage using a multimeter, do you observe the expected voltage?

- Is the analog output voltage being processed in any way before being fed back into the analog input?  
For example:

- Are you seeing this offset of `8` consistently across the entire operating range?  
For example, if you set the constant value to `10`, does the ADC reading become `2`?