Eight 24-Bit Analog Inputs DAQ 8-Layer Measurement offset errors

jdrexler
8/9/25, 4:43 PM

Hello,
We are experiencing an issue with the measurement accuracy of the RPi expansion board Eight 24-Bit Analog Inputs DAQ 8-Layer (SM-I-022), which is brand new, recently purchased. The board is powered by 12 V, and for testing we are measuring a voltage of 5 V.

Power Supply 12V:

Voltage 5V applied to inputs 7 and 8:

1.) Testing input 7
Before connecting input 7, we read a value of -0.000066. After connecting a 5 V input (+ and GND), we read a value of 3.686978 (difference 1.3130 V relative to 5 V).

2.) Testing input 8
Before connecting input 8, we read a value of 0.000006. After connecting a 5 V input, we read a value of 3.690599 (difference 1.609407 V relative to 5 V).

Here is a snippet from the console:

The gain for both channels is set to 0. After running the calibration of input 7 at 5 V, the reading remains the same. I have updated the board’s firmware, but the results are still the same. This issue occurs on all inputs.

Could you advise what might be causing this issue?
Thank you,
Jan

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alexburcea Staff member
8/9/25, 5:58 PM

Hi Jan,

We recently discovered that we have a bug in the firmware, and we took care of it. Please update the card firmware, instructions here.
Anyway, for good results, you need to calibrate the card.

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A

Alex Admin
8/10/25, 3:04 PM

Hi,

The latest firmware version is 1.4.

Calibration must be done at two points to be complete. The two points must be as close as possible to the two ends of the measurement scale for good results.

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jdrexler
8/10/25, 3:43 PM

Hello Alex,
Thank you for the information. I tried the firmware update, but it looks the same as before.

Board firmware version is 1.4.

Without input:

With 5V input:

After calibration for 5V:

Do I have the correct firmware version, please? Am I using the commands correctly?

Thank you,
Jan

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alexburcea Staff member
8/10/25, 5:28 PM

We are migrating our forum, you can find this post here: https://sequentmicrosystems.com/community/forum/topic/195735/eight-24-bit-analog-inputs-daq-8-layer-measurement-offset-errors

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jdrexler
8/10/25, 5:43 PM

Thank you, Alex.
Just for clarification — does "Calibrate input channel, the calibration must be done in 2 points" mean that I should connect a known voltage (for example, 5 V) to differential input 1 (+ and –) and run the command: 24b8vin 0 cal 1 5
Then, reconnect the same voltage to input 2 (+ and –) and run the command: 24b8vin 0 cal 2 5
And that’s all?
Or could you please explain what exactly is meant by “calibration must be done in 2 points”?
Thank you,
Jan

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