Post History
Your question is answered in the very next sentence in the datasheet after the one you quoted: This split-burden resistor configuration ensures that the waveforms fed to the positive and negative...
#4: Post edited
by
Olin Lathrop
·
2025-04-03T11:55:42Z (about 6 hours ago)
- Your question is answered in the very next sentence in the datasheet after the one you quoted:
- <blockquote>This split-burden resistor configuration ensures that the
- waveforms fed to the positive and negative terminals of the ADC are 180 degrees out-of-phase with each other, which provides the best THD results with this ADC.</blockquote>
- Any measurement system will have some non-linearities. Such non-linearities create frequencies in the result that were not in the input. We call those fictitious frequency components "distortion".
- The non-linear effects are probably not symmetrical about the analog input midpoint. By driving both inputs with an equal but opposite signal, the result does become symmetric, cancelling out some of the non-linear effects.
- <h2>Added</h2>
- I see Andy's answer mentions another effect. His answer isn't technically about THD (total harmonic distortion), but is nonetheless another issue you should consider. You want to ignore common mode signals caused the the capacitance between the primary and secondary in the current transformer, while measuring only the differential mode signal.
- The suggested circuit addresses both issues simultaneously (THD and common mode noise rejection).
- <blockquote>The part I don't "see" is how split-burden configuration ensures that the waveforms fed are 180 degrees out-of-phase with each other</blockquote>
- The transformer secondary puts out a voltage that the A/D is supposed to measure. It doesn't care how you interpret this voltage.
- If you ground the bottom end, then you can consider the top end to be the output voltage. If you ground the top end, then the bottom end is the output voltage, although flipped in sign compared to the previous. You could say that grounding the bottom gives you the full positive voltage at top, and grounding the top gives you the full negative voltage at bottom.
If this secondary had a center tap and you grounded it, then you'd get half the positive voltage at top and half the negative of that at bottom. Splitting the burden resistor and grounding its center point achieves the same thing in this case. Half the secondary output will be across the top Rb, and the other half across the bottom Rb. If you consider the center 0 V, then the top will be positive and the bottom negative. They will have that same magnitude, but negative of each other. That's the same as 180° out of phase.
- Your question is answered in the very next sentence in the datasheet after the one you quoted:
- <blockquote>This split-burden resistor configuration ensures that the
- waveforms fed to the positive and negative terminals of the ADC are 180 degrees out-of-phase with each other, which provides the best THD results with this ADC.</blockquote>
- Any measurement system will have some non-linearities. Such non-linearities create frequencies in the result that were not in the input. We call those fictitious frequency components "distortion".
- The non-linear effects are probably not symmetrical about the analog input midpoint. By driving both inputs with an equal but opposite signal, the result does become symmetric, cancelling out some of the non-linear effects.
- <h2>Added</h2>
- I see Andy's answer mentions another effect. His answer isn't technically about THD (total harmonic distortion), but is nonetheless another issue you should consider. You want to ignore common mode signals caused the the capacitance between the primary and secondary in the current transformer, while measuring only the differential mode signal.
- The suggested circuit addresses both issues simultaneously (THD and common mode noise rejection).
- <blockquote>The part I don't "see" is how split-burden configuration ensures that the waveforms fed are 180 degrees out-of-phase with each other</blockquote>
- The transformer secondary puts out a voltage that the A/D is supposed to measure. It doesn't care how you interpret this voltage.
- If you ground the bottom end, then you can consider the top end to be the output voltage. If you ground the top end, then the bottom end is the output voltage, although flipped in sign compared to the previous. You could say that grounding the bottom gives you the full positive voltage at top, and grounding the top gives you the full negative voltage at bottom.
- If this secondary had a center tap and you grounded it, then you'd get half the positive voltage at top and half the negative of that at bottom. Splitting the burden resistor and grounding its center point achieves the same thing in this case. Half the secondary output will be across the top Rb, and the other half across the bottom Rb. If you consider the center 0 V, then the top will be positive and the bottom negative. They will have the same magnitude, but negative of each other. That's the same as 180° out of phase.
#3: Post edited
by
Olin Lathrop
·
2025-04-03T11:54:34Z (about 6 hours ago)
- Your question is answered in the very next sentence in the datasheet after the one you quoted:
- <blockquote>This split-burden resistor configuration ensures that the
- waveforms fed to the positive and negative terminals of the ADC are 180 degrees out-of-phase with each other, which provides the best THD results with this ADC.</blockquote>
- Any measurement system will have some non-linearities. Such non-linearities create frequencies in the result that were not in the input. We call those fictitious frequency components "distortion".
- The non-linear effects are probably not symmetrical about the analog input midpoint. By driving both inputs with an equal but opposite signal, the result does become symmetric, cancelling out some of the non-linear effects.
- <h2>Added</h2>
- I see Andy's answer mentions another effect. His answer isn't technically about THD (total harmonic distortion), but is nonetheless another issue you should consider. You want to ignore common mode signals caused the the capacitance between the primary and secondary in the current transformer, while measuring only the differential mode signal.
The suggested circuit addresses both issues simultaneously (THD and common mode noise rejection).
- Your question is answered in the very next sentence in the datasheet after the one you quoted:
- <blockquote>This split-burden resistor configuration ensures that the
- waveforms fed to the positive and negative terminals of the ADC are 180 degrees out-of-phase with each other, which provides the best THD results with this ADC.</blockquote>
- Any measurement system will have some non-linearities. Such non-linearities create frequencies in the result that were not in the input. We call those fictitious frequency components "distortion".
- The non-linear effects are probably not symmetrical about the analog input midpoint. By driving both inputs with an equal but opposite signal, the result does become symmetric, cancelling out some of the non-linear effects.
- <h2>Added</h2>
- I see Andy's answer mentions another effect. His answer isn't technically about THD (total harmonic distortion), but is nonetheless another issue you should consider. You want to ignore common mode signals caused the the capacitance between the primary and secondary in the current transformer, while measuring only the differential mode signal.
- The suggested circuit addresses both issues simultaneously (THD and common mode noise rejection).
- <blockquote>The part I don't "see" is how split-burden configuration ensures that the waveforms fed are 180 degrees out-of-phase with each other</blockquote>
- The transformer secondary puts out a voltage that the A/D is supposed to measure. It doesn't care how you interpret this voltage.
- If you ground the bottom end, then you can consider the top end to be the output voltage. If you ground the top end, then the bottom end is the output voltage, although flipped in sign compared to the previous. You could say that grounding the bottom gives you the full positive voltage at top, and grounding the top gives you the full negative voltage at bottom.
- If this secondary had a center tap and you grounded it, then you'd get half the positive voltage at top and half the negative of that at bottom. Splitting the burden resistor and grounding its center point achieves the same thing in this case. Half the secondary output will be across the top Rb, and the other half across the bottom Rb. If you consider the center 0 V, then the top will be positive and the bottom negative. They will have that same magnitude, but negative of each other. That's the same as 180° out of phase.
#2: Post edited
by
Olin Lathrop
·
2025-04-02T15:39:45Z (1 day ago)
- Your question is answered in the very next sentence in the datasheet after the one you quoted:
- <blockquote>This split-burden resistor configuration ensures that the
- waveforms fed to the positive and negative terminals of the ADC are 180 degrees out-of-phase with each other, which provides the best THD results with this ADC.</blockquote>
- Any measurement system will have some non-linearities. Such non-linearities create frequencies in the result that were not in the input. We call those fictitious frequency components "distortion".
The non-linear effects are probably not symmetrical about the analog input midpoint. By driving both inputs with an equal but opposite signal, the result does become symmetric, cancelling out some of the non-linear effects.
- Your question is answered in the very next sentence in the datasheet after the one you quoted:
- <blockquote>This split-burden resistor configuration ensures that the
- waveforms fed to the positive and negative terminals of the ADC are 180 degrees out-of-phase with each other, which provides the best THD results with this ADC.</blockquote>
- Any measurement system will have some non-linearities. Such non-linearities create frequencies in the result that were not in the input. We call those fictitious frequency components "distortion".
- The non-linear effects are probably not symmetrical about the analog input midpoint. By driving both inputs with an equal but opposite signal, the result does become symmetric, cancelling out some of the non-linear effects.
- <h2>Added</h2>
- I see Andy's answer mentions another effect. His answer isn't technically about THD (total harmonic distortion), but is nonetheless another issue you should consider. You want to ignore common mode signals caused the the capacitance between the primary and secondary in the current transformer, while measuring only the differential mode signal.
- The suggested circuit addresses both issues simultaneously (THD and common mode noise rejection).
#1: Initial revision
by
Olin Lathrop
·
2025-04-02T15:35:37Z (1 day ago)
Your question is answered in the very next sentence in the datasheet after the one you quoted: <blockquote>This split-burden resistor configuration ensures that the waveforms fed to the positive and negative terminals of the ADC are 180 degrees out-of-phase with each other, which provides the best THD results with this ADC.</blockquote> Any measurement system will have some non-linearities. Such non-linearities create frequencies in the result that were not in the input. We call those fictitious frequency components "distortion". The non-linear effects are probably not symmetrical about the analog input midpoint. By driving both inputs with an equal but opposite signal, the result does become symmetric, cancelling out some of the non-linear effects.