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I am designing a system to measure for load cells with the following characteristics:
- Sensitivity of 2mV/V
- Accuracy class of 3000
- Input Voltage of 10V
- Max load 20kg
- Min load 10gr
- Only Force in one direction is measured
The system is power with 24V. I am using two LMR14203: One for the Analog circuit (10V) and other for the Digital Circuit (5V).
So far I am using INA826 in my simulations to amplify the load cell voltage and everything works nice.
My concern is about the ADC conversion. I was thinking in an ADC with 20bit with ratiometric measurement, but I don't find any ADC with
an Analog Input Ref Voltage of 10V. What do you think about everything? Is there and ADC with 10V analog ref?
Can I use ratiometric measurement in some way with an ADC with 5V analog ref?
Thank you so much for your help!
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In reply to Daniel Casale Linde:
What ADC have you been using thus far?
If you are looking for a sample and hold ADC, commonly known as SAR ADCs, it is not common to use a 20 bit SAR ADC in a ratio metric reference design. This is considered high precision devices, and need the reference input to be clean and stable.
It is not necessary for the device to have a reference of 10V to obtain an input range up to 10V, thus I doubt you will find any ADC with such a high reference input; devices are designed to be able to use a 2.5V or sometimes 5V reference to be able to extend their input range to 10V. You will need to focus on the driving input circuit design of the ADC, as the reference for your application will not be able to be used for a ratiometric design.
There are ADC input designs in the ADC Cookbook that I think will prove helpful.
In reply to Cynthia:
In reply to Bob Benjamin:
There are some great advantages using a ratiometric measurement as the noise and drift of the excitation source cancels for load cell measurement. Also, when using the internal PGA of an ADC the input referred noise lowers with applied gain. Using an external amplifier will not do this.
When you add an external amplifier with a a non-ratiometric measurement, you add external noise, drift (both offset and gain) of the amplifier the excitation source and the ADC reference. It is unfortunate that the 10V excitation is a requirement as this complicates things considerably.
Your request for components to use is difficult to answer without some more specific information. It is like asking for a good soup without knowing what you like for flavors or ingredients. You mentioned the load cell sensitivity and the requirement for 10V excitation, but how often do you want to receive new conversion data (or the data rate output of the ADC) and what scale resolution are you trying to achieve (or minimum stable scale resolution)?
After a few days of studying the problem we concluded that is going to be easier and cheaper to change the 10V requirement.
I have been comparing several ADS and the ADS1231 is a good recommendation.
Thanks for your help.
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