5568dec4ad
git-svn-id: https://bucket.mit.edu/svn/nilm/zoom@7010 ddd99763-3ecb-0310-9145-efcb8ce7c51f
56 lines
1.1 KiB
Plaintext
56 lines
1.1 KiB
Plaintext
Setup
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-----
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Total input current Ic (amps)
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LA-55 with ~200 turns, 1k burden.
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Voltage output is Vc = (Ic / 1000 * 1k) = Ic
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LA-55 output goes to trimmable offset opamp,
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trimmed to 0 when DAC command is 32768.
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-> NOTE: DC offset changes a ton (200mV!) when the LA-55 is
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saturated one way versus the other, then returned to zero.
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Will try implementing a degauss feature, to see if the DC offset
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always settles to the same amount. Result: seems to work.
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R36 = 1k (shouldn't matter)
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IC3A:
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R37 = 1k, R38 = 3.3k -> scales up by 4.3
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IC3B:
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R39 = 100k
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R40 = 100k
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R41 = 100k
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R42 = 100k
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Reference:
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R43 and R44 are a pot, trimmed so R43 == R44 -> VREF1.25 = 1.25V.
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So
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ADC12V+ = 1.25 - (4.3 * Vc)
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= 1.25 - 4.3 Ic
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PIC input value (PICV) is:
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0 = 0V
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2048 = 2.5V
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PICV = (ADC12V+ * 2048 / 2.5)
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PICV = (1.25 - 4.3 Ic) * 2048 / 2.5
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PICV = 1024 - 3522.6 Ic
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Ic = (1024 - PICV) / 3522.6
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Computed by adc12_to_current()
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Scaling
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-------
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DAC can do about ±20A. DAC command (DACC) is:
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0 = -20A
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65536 = +20A
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DACC = 32768 * (1 + Ic / 20)
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Computed by current_to_dac()
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Code
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----
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