I schould design a load cell signal chain. My configuration is:
- load cell: 0.55mV/V at 5000kg
- load cell supply: not define yet: 5V give a poor sensibility. I think 8V is good because my system schould work between 9V - 16V.
I can not go higher than 8V regulated. (or solution are welcome)
- I have several load cell connected: (3 to 8) and I want to read each load cell signal separatly.
- I need to have 1 kg resolution.
- In the best case I need to read 1 convertion / channel per 10ms. in bad case in 100 ms.
For low input signal (as in my application) I schould use a gain of 128 + reduce the ADC reference voltage to ~1.2V.
This way I got a ADC range of +- 10mV. But I schould divide the sensor supply by 8.
- 1 - How can I estimate the noise of the ADC for other reference? (like 1.2V ^^)
- 2 - I need an advice concerning a quick noise estimation.
Using only the ADC part, I have a noise of 121nV. It means I schould add this voltage to the signal I give at the output.
=> 0.55mV/V under 8V for 5T => I got ~0.9 kg / free noise count. @ 960 Hz
Using an amplifier befor the ADC (AD8226 for example) It adds 22nV / sqrt(Hz) at it input.
=> I anderstand as: if I considere 1kHzbandwidth (with a passive anti aliasing RC filter befor the AD8226 inputs) It means I add 0.6µV noise before amplification. That give lower performance than without the amplifier.
Where is my error?
- 2.1 - How does the setling time works? Schould I wait this time before each convertion?
Regarding the previous points, I also consider an architecture using 2 AD7797 (single channel 24bt ADC with fied gain (128)) and multiplexer (ADG1409).
The output frequency is 123 Hz, but by using 2 parts, I can have the data from all my channel in a good time.
- 3 - Do you have advices for an architecture that match my objectives?
A lot of solution semms to be possible, but may be they are not all pertinent.