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Noise Floor - 5000 series - 4227

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Noise Floor - 5000 series - 4227

Postby BSI » Thu Oct 30, 2014 5:57 pm

Hi

As per the 5000 series specs, noise figures are presented as :
Noise (on 50 mV range) :

8-bit mode 120 μV RMS
12-bit mode 110 μV RMS
14-bit mode 100 μV RMS
15-bit mode 85 μV RMS
16-bit mode 70 μV RMS

Does this noise represent the AC RMS noise or True RMS noise (--> including the DC component) ?

For comparison, a 4227 on 50mV range with no cable connected to the input produces on a bench test:
average RMS noise: 85 uV
True RMS noise: 250 uV
as measured in Picoscope, with: 50ms time windows, and 1MS settings.
What is the 4227 specs noise please?

Thx
L.
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Re: Noise Floor - 5000 series - 4227

Postby Hitesh » Tue Nov 18, 2014 12:05 pm

Hi L.,

Apologies for the delay in someone responding to your post.

The measurement given is AC RMS.

With regards to noise specs for the PicoScope 4227, this is being investigated and I will provide an update.

Update: After speaking to a Hardware Engineer, the 85uV AC RMS should be in the typical range. It may vary depending on the device.

Regards,
Last edited by Hitesh on Tue Nov 18, 2014 12:30 pm, edited 1 time in total.
Reason: Added update
Hitesh

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Re: Noise Floor - 5000 series - 4227

Postby BSI » Tue Nov 18, 2014 4:17 pm

Thx Hitesh,

So what would be the DC RMS for the 5000 please?

So does this mean a 12-bit 4227 has:
- similar noise level than a 5000 in 15-bit mode (!)?
- better noise level than a 5000 in 8, 12, 14 -bit modes?

Thx
L.
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Re: Noise Floor - 5000 series - 4227

Postby Hitesh » Wed Nov 19, 2014 1:16 pm

Hi L,

The DC offset is considered to be part of the accuracy specifications, which noise measured in AC RMS.

I ran some further tests and found that the AC RMS for the PicoScope 4227 is around 70uV (there is a bug in PicoScope 6.10.6.1 in relation to this measurement in block mode captures which has been reported).

I've spoken to one of our Hardware Engineeers and the PicoScope 4227 and 5000 Series are completely different designs. The PicoScope 5000 Series can have a bandwidth of up to 200MHz, which leads to more noise in comparison to the PicoScope 4227 which has a 100MHz bandwidth.

The PicoScope 5000 Series oscilloscopes has a 20MHz filter which increases the signal to noise ratio of the scope.

The noise that you see on a PicoScope is mostly thermal and thus can be averaged using a maths channel in the PicoScope 6 software allowing for more accurate DC measurements.

I hope this helps.
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Re: Noise Floor - 5000 series - 4227

Postby BSI » Wed Nov 19, 2014 4:53 pm

Hi Hitesh.

Thanks for the further info. Yes I understand 4227 and 5000 series are different, nevertheless the performance does not seem drastically improved. Noise floor is really important to pick up small signals, independently of the bit resolutions.

The specs on the 5000 state a RMS noise as copied in the first post in this thread, but it does not specify which of the bandwidth these figures refers to: is it for 60 MHz, 100MHz, or 200 MHz ? And whether or not the filter was applied to produce these figures ? Based on the available figures, it still seems to me, that the 4227 with 70uV like you state, performs better than the 5000 in most cases in terms of noise. I would like to be wrong, as the 4227 is no longer available.
Cheers,
L.
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Re: Noise Floor - 5000 series - 4227

Postby Hitesh » Thu Nov 20, 2014 12:41 pm

Hi L.,

The tests on the PicoScope 5000 Series were carried out at full bandwidth (otherwise it would have been stated). The use of the 20MHz filter would also have been stated if it formed part of the test.

The PicoScope 5000 Series has a slightly higher noise due to the extra bandwidth. Noise in terms of nV/√hz is better on the 5000 series. PS4227 is 7nV/√hz vs 6nV√hz for the PS5000 (15bit mode).

I hope this helps.

Regards,
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Re: Noise Floor - 5000 series - 4227

Postby BSI » Thu Nov 20, 2014 6:00 pm

Thx Hitesh.
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