magnaparva Posted March 3, 2016 at 05:47 PM Share Posted March 3, 2016 at 05:47 PM I seem to be getting confused by the resolution/accuracy quoted. The Industrial Dual Analog In Bricklet quotes a resolution of 24bit, which on the 70VDC full scale would give (70/2^24) roughly 4 micro volts resolution. The accuracy is quoted as 4mV. Is the resolution really 1000 times better than the accuracy? Quote Link to comment Share on other sites More sharing options...
borg Posted March 3, 2016 at 09:36 PM Share Posted March 3, 2016 at 09:36 PM Basically, yes. To achieve real 24bit accuracy you would need a crazy expensive analog frontend in front of the adc. This is out of the reach of a Bricklet. The performance of the Bricklet is comparable to a modern highish end 30000 count multimeter (e.g. http://www.amazon.com/Agilent-U1272A-Handheld-Counts-True/dp/B004URG9EU). The big difference is of course that the multimeter not only has a +-30V range but also a +-30mV range. Edit: Do you need a really high resolution in the full +-35V range? Or would a +35mV version of the Bricklet help in your application? Quote Link to comment Share on other sites More sharing options...
magnaparva Posted March 4, 2016 at 08:53 AM Author Share Posted March 4, 2016 at 08:53 AM Thanks for the speedy reply! I am measuring a 0-5V signal, where ideally I would like to achieve an accuracy of +-1mV. If I could get the range down to a 6th of current, that would give +-5.83V range which assuming the accuracy would be also be 6 times improved would work for our application. Would it be as simple as exchanging R8 and R10 to 4k7/6 resistor? Going for something readily available, like a 787 ohm (e.g. http://uk.farnell.com/1752470)? Edit: Resistor labels changed to read R8 and R10 Quote Link to comment Share on other sites More sharing options...
batti Posted March 7, 2016 at 07:10 AM Share Posted March 7, 2016 at 07:10 AM The circuit uses a differential amplifier as "frontend" (link to schematic). This amplifier multiplies the input voltage by R8=R10/R13=R14. Please note the formula in the lower right corner of the schematic. By changing the resistors R8,R10,R13,R14 you can adapt the measurement range according to your needs. Quote Link to comment Share on other sites More sharing options...
magnaparva Posted March 7, 2016 at 04:51 PM Author Share Posted March 7, 2016 at 04:51 PM Ah yes, sorry, I meant to say R8 and R10 in my last post and should have multiplied the resistor by 6 rather than divide. If I change both R8 and R10 to be 33k (e.g. http://uk.farnell.com/1717610) and leave R13 and R14 at 280k, I should be able to get a range of +-5.09V (at the input to the U1B) to provide the required 0.6V the ADC0 net. Will I then need to recalibrate U4? to convert the reading would it be as simple as dividing the result from the API by 7.021 (based on 35.745/5.091)? Quote Link to comment Share on other sites More sharing options...
Schnaki Posted March 9, 2016 at 10:25 AM Share Posted March 9, 2016 at 10:25 AM @magnaparva Have you try the modification? Quote Link to comment Share on other sites More sharing options...
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