9V Voltage and Micro Amperes

Hello,
how can I measure micro Amperes while measuring the current
of an 9V power supply? I made an try with an shunt resistor (50mOhms),
but the signal I got was very noisy.

Best regards

Hi and welcome to the forum.

Maximum voltage on all pins of Otii Arc is 5V (except DC plug) and if you exceed this then your Arc might get damaged. So it is not possible to measure a 9V device by using ADC input.

The only way to get to 9V is by connecting like this:


The external power supply must be isolated and 5V or lower not to damage your Otii Arc (do not exceed 5V).
The current consumption measurement will be correct (but might be noisy due to the added power supply) but the voltage and energy measurement will be wrong.
Otii Arc Main - connector is GND, that’s why you MUST have an isolated power supply, otherwise you will get a short circuit and you might damage your Otii Arc and other equipment.

Best regards,
Björn

OK, thanks. Is there any documentation which descripes the inputs of the OTII? What makes the Sense pin for example? In the documentation I can’t find any description of the inputs.

Hi,

You can find information here:


The Tech Spec is also found in the end of this page.

Sense is used as two separate voltage measurements or, if you enable 4-wire, used to compensate for voltage drop in your power cables.

Best regards,
Björn

And that is the whole documentation/manual for an 500$ device? An table with technical information and an webpage with the headline features?

Hi,

I am not sure what information you are looking for but I am happy to help you.
Could you be more specific?

Best regards,
Björn

What is for example the 5V pin on the front? Can I use it for measurement?What is the idea behind it? What is the maximum/minimum current of it? And where can I get these information besides asking in this forum?

Hi,

Thank you for your feedback it is very valuable.

The +5V pin is a constant 5V supply, maximum 500mA, that is enabled either in the GUI (see picture) or via scripting.
image
To use this, you might also want to use an external DC adapter, not only power through USB, otherwise the voltage will be below 5V (if a voltage below 5V is acceptable then you do not need the power supply).

The idea behind this is in automation, where you can power a switchboard that Otii Arc controls via the GPIOs and/or UART, for example in a continuous integration setup.
An example of a setup with Jenkins can be found here:

Best regards,
Björn

Ok, thanks. I have another question. Where can I lock the high current range so that output voltage is 5V ?

Hi,

In Otii application, you open Project Settings and go to tab Current, there you can disable Auto range.
By disabling auto range you set you Otii Arc in high current range.

Best regards,
Björn

OK, thanks. This works! But I think things like that should stand in an manual. But asking here is also fine.

The only problem is, that when I use 5 Volt the measurement results are wrong (negativ current). I made two screenshots of the same signal of an microcontroller with an buck converter. The noisy one is (5V), the clear and correct one 4.5V. Is there any possibility to get correct results for the 5V? :

Hi,

In the clear recording, the measurement is done in highest accuracy (auto range turned on) and the noisy one is done in high range (auto range turned off).
There is a huge difference in resolution between low range and high range. The step size in low range is 5nA and in high range a little bit below 100uA, and you measure a signal of 2uA.

To get correct result for this recording you must have auto range turned on and that limits you to 4.55V.

Best regards,
Björn