| Products > Test Equipment |
| Oscilloscope input noise comparison |
| << < (5/27) > >> |
| Keysight DanielBogdanoff:
Thanks for doing this! I'm also interested in how you measured noise. We generally use the smallest hardware V/div setting and measure V RMS (NOT Peak-Peak). This makes sure you don't have any issues with the quantity of acquisitions/update rate. |
| rsjsouza:
--- Quote from: Keysight DanielBogdanoff on October 19, 2018, 09:53:32 pm ---Thanks for doing this! I'm also interested in how you measured noise. We generally use the smallest hardware V/div setting and measure V RMS (NOT Peak-Peak). This makes sure you don't have any issues with the quantity of acquisitions/update rate. --- End quote --- Interesting, Daniel. Have you ever seen any manufacturers skew or butcher RMS measurements that could lead to incorrect results? |
| nctnico:
--- Quote from: Keysight DanielBogdanoff on October 19, 2018, 09:53:32 pm ---Thanks for doing this! I'm also interested in how you measured noise. We generally use the smallest hardware V/div setting and measure V RMS (NOT Peak-Peak). This makes sure you don't have any issues with the quantity of acquisitions/update rate. --- End quote --- I'm wondering if that is the best way of doing it on an oscilloscope which uses decimated data for on-screen measurements. Also the RMS peak measurement may be affected by any DC offset in the signal. Using the actually sampled data and doing a noise spectrum analysis seems like a much better way to me. |
| Rich@RohdeScopesUSA:
--- Quote from: nctnico on October 19, 2018, 10:34:20 pm --- --- Quote from: Keysight DanielBogdanoff on October 19, 2018, 09:53:32 pm ---Thanks for doing this! I'm also interested in how you measured noise. We generally use the smallest hardware V/div setting and measure V RMS (NOT Peak-Peak). This makes sure you don't have any issues with the quantity of acquisitions/update rate. --- End quote --- I'm wondering if that is the best way of doing it on an oscilloscope which uses decimated data for on-screen measurements. Also the RMS peak measurement may be affected by any DC offset in the signal. Using the actually sampled data and doing a noise spectrum analysis seems like a much better way to me. --- End quote --- We typically recommend the same method Daniel suggested (smallest volt/div setting, AC RMS or std deviation or a vertical histogram) with one addition (which I think Daniel would agree with) - you should really figure it as a percent of full scale as some oscilloscopes have 10 vertical divisions and some only have 8. Of course the other key thing to keep in mind when measuring noise using this method is that noise is a function of BW. So you may need to use filters to get an apples to apples compare. -Rich |
| David Hess:
--- Quote from: Rich@RohdeScopesUSA on October 20, 2018, 03:07:22 am ---you should really figure it as a percent of full scale as some oscilloscopes have 10 vertical divisions and some only have 8. --- End quote --- It is even more complicated than that. The number of ADC counts per division varies between DSO designs and has little to do with the number of displayed divisions. For instance 25 counts per division is (or was) common producing a 10.2 division "virtual" display of which either 10 or 8 vertical divisions might be visible. My DSOs all use 5:4 displays so 8 vertical divisions with an extra division and then some at the top and bottom so clipping it usually outside the range of the display. It should always be possible to convert to microvolts RMS within a given bandwidth and nV/SqrtHz versus frequency based on the noise measurement and vertical sensitivity. |
| Navigation |
| Message Index |
| Next page |
| Previous page |