Q: I would like to use the ADuCM350 to do potentiostat type measurements ?
A: Please refer to AN-1281 and the Amperometric example code in the Software Development Kit. Details in Featured Content on ADuCM350 Engineerzone homepage.
Q: Can I put a +200mV step on sensor ? See AN-1281+ details n Featured Content on ADuCM350 Engineerzone homepage.
A: Yes. At time=0, the system is calibrated so that no voltage across sensor (both sides precisely calibrated to 1.1V).
At time=1, the DAC can output 1.3V to give a DC step across sensor of 200mV.
Q: I have changed RCAL/RTIA on my board, how do I reflect this change in the Amperometric Measurement example from the SDK?
A: Please refer to the following: http://ez.analog.com/docs/DOC-11063
In this case we did use the Eval-ADUCM350 motherboard, but there was some noise in the measurement. When we built an optimised board, we were able to achieve a higher resolution with the noise significantly reduced.
When you did this measurement where you could get the "ADuCM350" to see the 50 pA steps .... were you using the Eval-ADuCM350EBZ? Or some other board or some other setup?
What I mean is that we have set up an experiment using an appropriate TIA feedback resistor which would allow us to measure a current range from 0A - 1uA. In this case, we were supplying a current (from an accurate current source) into the receive channel of the ADuCM350, starting from 0A and increasing in 50pA steps to 1uA. We were able to measure the discrete 50pA steps. Doing this on the Eval-ADUCM350EBZ hardware is not optimal though, as the layout of the board is not optimised for these tiny currents and is therefore susceptible to noise. It is hard to say if the board could reliably measure the difference between 1 and 1.2nA as it would depend on noise. With an optimised board, the ADuCM350 should be able to measure with that resolution though.
Could you clarify what "1uA current range in 50pA steps" means in practical terms? I'm not an engineer so I tend to get a bit lost when it comes to this stuff. Could the board reliably measure the difference between say 1 and 1.2 nA or is anything under 1 µA difficult?
At the moment, any updates are being concentrated on the firmware/SDK, so in the short term DC measurement capabilities will not be added to the EKSP software. Implementing DC measurements using the SDK is facilitated by a large suite of AFE APIs and example projects.
There are ongoing experiments with large loads (and therefore very small currents) and the ADuCM350 receive channel has successfully measured a 1uA current range in 50pA steps. Optimising PCB layout to reduce noise is critical at this level of current. A white paper / application note will be published with the findings of these experiments once they are completed.