[MAGEEC] Accuracy of the power measurement shield

[Jeremy Bennett]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi Mark,

You'll see I have updated the Wiki in line with my email. Looks like
the ADCs are actually 12-bit.

Best wishes,


Jeremy

On 06/03/18 16:48, Jeremy Bennett wrote:
> On 06/03/18 16:26, Mark Kettner wrote:
>> Hello everyone,
> 
>> could someone please tell me the accuracy of the measurement 
>> shield. How can I assume really low power (milli or micro) are 
>> still valid measurements and not just noise? Or is this purely 
>> affected by the selected resistor?
> 
> Hi Mark,
> 
> Good to hear from you. James Pallister and Simon Hollis reckoned
> the measurement is accurate to 1%.
> 
> I'm out of the office at the moment, so don't have a board to look
> at. - From memory it uses a 10 bit ADC. To measure the current, the
> inserted resistor aims to create a maximum 50mV drop. The largest
> resistor on the board is 5R, which would therefore be for a peak
> current of 10mA. There is an option to insert a larger resistor if
> you wish. Voltage range is fixed I think at 0-6V.
> 
> The circuit was designed to sample at up to 2MHz on each sample
> point, although at that frequency I would expect inductive and
> capacitive affects to impact on the accuracy. The standard tool is
> written in Python and in my experience struggles to sample at much
> more than 10kHz. However the design is fully open, so there is no
> problem with modifying the tool and/or the firmware to sample at
> these higher rates. You can find the software on GitHub.
> 
>> Unfortunately I couldn't find anything about that in the wiki.
> 
> Since the MAGEEC work finished some time ago, I've been less
> proactive in updating the wiki. However I'm happy to add some notes
> about this. I'll check the facts against the board when I get
> back.
> 
> Best wishes,
> 
> 
> Jeremy
> 
>> -- Mit freundlichen Gruessen / Best Regards
> 
>> Mark Kettner _______________________________________________
>> mageec mailing list mageec at mageec.org 
>> http://mageec.org/cgi-bin/mailman/listinfo/mageec
> 
> 
> 

- -- 
Tel:     +44 (1590) 610184
Cell:    +44 (7970) 676050
SkypeID: jeremybennett
Twitter: @jeremypbennett
Email:   jeremy.bennett at embecosm.com
Web:     www.embecosm.com
PGP key: 1024D/BEF58172FB4754E1 2009-03-20
-----BEGIN PGP SIGNATURE-----

iGMEARECACMFAlqimQMcHGplcmVteS5iZW5uZXR0QGVtYmVjb3NtLmNvbQAKCRC+
9YFy+0dU4QmEAJ9YG8ywhGGXH/US6vvW0q4uoZIKPACeIcZaCr4bxf6eC/0lnjQP
o8lTC/E=
=FCnR
-----END PGP SIGNATURE-----