bbc7dcdba4
git-svn-id: https://bucket.mit.edu/svn/nilm/zoom@7008 ddd99763-3ecb-0310-9145-efcb8ce7c51f
29 lines
1.0 KiB
Plaintext
29 lines
1.0 KiB
Plaintext
Given out scaling and that n=300 on the secondary for the CT 0.1-P,
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and a 16-bit DAC value, each LSB cancels out 900 µA of current on
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the primary, for a maximum range of
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DAC 0000h ≈ -29.5 A (-900 µA * 2^15)
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DAC 8000h ≈ 0.0 A
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DAC ffffh ≈ 29.5 A (900 µA * 2^15)
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Let's use 14 bits from the DAC plus 4 bits from the CT to get 18 bits
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total. Analysis is over the positive range only for simplicity:
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The range covered by a LSB on the DAC would be
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29.5A / 2^14 = 1.8 mA.
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CT range should overlap slightly, so intend on measuring 2.5mA.
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CT output is 5V at 100mA, so output is 125mV at 2.5mA.
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To get 4 bits from that, we need to measure 7.8mV
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PIC is measuring 12 bits over 2.5V which is 0.61mV.
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So we only need to shift the CT output and limit it:
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(PIC input) = clamp(0, 1.25V - (CT output), 2.5V)
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Clamp by putting a 1K in series with diodes to VSS/VDD.
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-----
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Results are not promising. The CT-0.1P does not want to behave
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reasonably when the secondary is connected to the current source.
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Earlier tests indicated it would, but now it's not...
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