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low current measurement

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low current measurement

Postby beka » Thu Jun 25, 2015 2:40 pm

I have to measure small currents (Voltage over a shunt) : 50mV. I want to know the accuracy of picoscope 5000? In the data sheet I read +-2% (+-5% of full scale in 12 bit mode and 10mV/div).
So my data can vary between 48,5mV and 51,5mV. Is my calculation wright?

Regards
Bernd
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Re: low current measurement

Postby AndrewA » Fri Jun 26, 2015 11:34 am

I have listed the specs below for the 5000 series.-
±50 mV to ±20 V ranges, 12-bit mode or greater ±0.25% typical @ 25°C (±1% of full scale max @ 20 to 30°C)
±50 mV to ±20 V ranges, 8-bit mode ±1% typical @ 25°C (±3% of full scale max @ 20 to 30°C)
±10 mV and ±20 mV ranges ±2% typical @ 25°C (±5% of full scale max @ 20 to 30°C)

If you are measuring around 50mV dc the best settings would be use the +-100mV range. And the resolution to 12-bits or greater.
So +-100mV - 200mV x 2.5% = +-0.5mV (typical at 25C)
And at 1%- 200mV x 1% = +-2mV (20C-30C)

If you are measuring less than 50mV, then use the +-50mV range-
+-50mV - 100mV x 2.5% = +-0.25mV (typical at 25C)
1%- 100mV x 1% = +-1mV (20C-30C)

So if you measured 50mV on the +-100mV range the you would quote the measurement as 50mV +-0.5mV
The actual value could be from 49.5mV to 50.5mV

Other tips to help
  • I would also increase the resolution to 16-bits or the highness allowable, depending on the number of channels enabled.
  • Also leave the scope running for 20 minutes for the internal temperature to become stable, for best results. And try to use the scope in a room temperature of 25 degrees Celsius.
  • Then zero the channel(s) before start your measurements, to remove any DC offset, from the channel.
Regards Andrew
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