AD7791 random values

Hi, 

Can you confirm what's the equivalent code for that? Is that a full scale code?  Is the issue happening at specific interval or just randomly? 

Can you also monitor the input and reference voltage? Is there a chance you can capture the issue while measuring the inputs mentioned?

Thanks,

Jellenie

Hi

At this time the values do not represent full scale of AD.
It's a random problem, I'll try to capture the voltage values on the inputs.
We have already assembled other devices and the effect is the same.

Thanks

Hi, 

May I know what is the code value? For example the 661.52 weight what is the equivalent input voltage for that? May I know also your sensor spec and sentivity? And is it also possible that you can schematic or is it really similar with the CFTL mentioned above? 

I think it is weird if it really appeared randomly. So we have to understand if the issue is causing by the hardware or a software. For example if you can isolate the sensor or front end for example and just short the inputs of the ADC are you also seeing the same peak measurement? 

Thanks,

Jellenie

Hi,

I removed R43 and R44 and shorted C49.

Random values return even when we perform ADC queries at intervals greater than 500ms

In other words, slow queries

Thanks,

Ivan

PCI_SD_022021.rar

Hi, 

Apologies. I cannot open the attached file, can you send atleast a pdf version of the schematic?

Thanks,

Jellenie

Hi,

No problem

PDF

Hi 

Thanks for sharing I will have a look at this again. May I know if you managed to monitor the physical input voltage and see if you find similar issues? 

Thanks,

Jellenie

In addition, you have mentioned above that when you disconnected the load cell, the issue is still there? May I know exactly what is the equivalent voltage of that random value? Is that the same voltage level when load cells are connected? I'm not sure if you already provided this info above. Can you explain this further please?

Thanks,

Jellenie

Hi

Sorry for the delay, there are other projects! We found no problems or fluctuations in the input voltage. We are currently performing two sequential readings and comparing the results. So we can discard what we judge to be wrong values.

But we keep investigating!

Hi

Thanks for the update, the temporary solution might be working for you but I agree we should still investigate and understand the root cause of the issue. 

I also noticed that you are using a switching regulator? Is that correct? What's the switching frequency and is it located near the device in your layout? Since it happened randomly, it is quite difficult to understand right ahead where the issue came from. But if you can narrow down each block of the system then that would be a good starting point. Like try to isolate the ADC or other part of the system. 

Thanks,

Jellenie