Hi, we have been using the Otii for a while and it has been working fine.
But, these current spikes and transients that occur every time there is a big change in current, are these real or some side effect of the hardware design?
See attached screenshot, in my opinion the real max current value is around 25 mA and minimum value 0 uA and not 65 mA and -406 uA. How can the current be negative ?!
Will there be any software update to filter these away?
Have you calibrated the Otii Arc before the measurement? (Device - Calibrate)
If not, that could explain some error measurement.
Also, what FW are you using?
You can see this in the History window when Otii Arc is connected.
Yes its calibrated. Hardware version is 1.1 and firmware version is 1.0.5.
Below is a screenshot from our measurement that shows better what i’m trying to explain. Every time there is a big change in current (positive or negative) there seems to be a glitch in current mesaurement. We also observed that the Arc main voltage is not stable at these glitches.
I tried to use an external 9V power supply and actually the glithes disappear. But instead there seems to be ripple on the current as well as voltage.
Any recommendations for the power supply? Some USB hub you can recommend or any brand recommendations for the external power supply?
The transients is due to that you have input capacitance on your device.
When your device increase the current consumption drastically, then the energy is firstly taken from your input capacitors (and cables etc), then Otii Arc needs to fill up that energy and that will create a current spike.
The opposite happens when the load decreases quickly.
We have seen bad behaviors for high current 9V DC adapters. Our experience is that a 9V DC adapter at max 2A is much better than higher current ones.
I am using a XP Power 9V 2.0A adapter but I have tried many that are good.
Thanks, we will do some more experiment and try to find a configuration that works for us.
These are the spikes I was also seeing - I wondered if it was localised inrush currents to our supply capacitors.
I’ll post-process the raw data to filter these out.
This thread saved me from having to re-setup the previous jig!
I have seen similar behavior after upgrading the Latest Arc SW and Latest OTII Software .
Regarding my test, I am using 3.7 Volts to power my device using USB and my Max peak is around 111mA a,d min is -369 µA (Sometimes teh -ve is around mAmps also). I have callibrated before starting tests also.
Can you check this behavior as this error makes the measurements go way wrong when we are dealing with µA
Note - Using the same kit, the minimum current was always presented correct in previous OTII versions.
So, the reason for these spikes are artifacts of the voltage regulation.
When the DUT (Device Under Test) change the load drastically, for example during a TX burst, the voltage drops. Otii Arc will then regulate the voltage to the set voltage, so it will step up the voltage internally. This creates a voltage difference between the regulator and the consumer, and current will flow to the DUT. This will be seen as a positive spike.
When the DUT then changes the load back, the opposite happens, and the current will flow back to the Otii Arc. This is why you can se negative measurements when the DUT goes back to sleep current, if the change is quick.
These two spikes will be equal in energy and will thus not affect the average.
Many thanks for your inputs.
Is there a workaround to mitigate this values to inch closer to real figures(By either having capacitance etc - Sorry I am not a HW guy)
Also is there a way where we can decide what to show in the screen (Purpose is to hide min Current unless this behavior is reolved). Any ideas.
You could downsample the recording.
This will eliminate the negative samples depending on your sleep current and how deep the negative spike was. If you have a really low sleep current and a big negative spike, then you need to downsample a lot, unfortunately.