Browse Source

notes

git-svn-id: https://bucket.mit.edu/svn/nilm/zoom@7010 ddd99763-3ecb-0310-9145-efcb8ce7c51f
tags/zoom-1.0
jim 12 years ago
parent
commit
5568dec4ad
1 changed files with 55 additions and 0 deletions
  1. +55
    -0
      notes/20081104.txt

+ 55
- 0
notes/20081104.txt View File

@@ -0,0 +1,55 @@
Setup
-----

Total input current Ic (amps)

LA-55 with ~200 turns, 1k burden.
Voltage output is Vc = (Ic / 1000 * 1k) = Ic
LA-55 output goes to trimmable offset opamp,
trimmed to 0 when DAC command is 32768.

-> NOTE: DC offset changes a ton (200mV!) when the LA-55 is
saturated one way versus the other, then returned to zero.

Will try implementing a degauss feature, to see if the DC offset
always settles to the same amount. Result: seems to work.

R36 = 1k (shouldn't matter)
IC3A:
R37 = 1k, R38 = 3.3k -> scales up by 4.3
IC3B:
R39 = 100k
R40 = 100k
R41 = 100k
R42 = 100k
Reference:
R43 and R44 are a pot, trimmed so R43 == R44 -> VREF1.25 = 1.25V.
So
ADC12V+ = 1.25 - (4.3 * Vc)
= 1.25 - 4.3 Ic

PIC input value (PICV) is:
0 = 0V
2048 = 2.5V

PICV = (ADC12V+ * 2048 / 2.5)
PICV = (1.25 - 4.3 Ic) * 2048 / 2.5
PICV = 1024 - 3522.6 Ic
Ic = (1024 - PICV) / 3522.6

Computed by adc12_to_current()

Scaling
-------
DAC can do about ±20A. DAC command (DACC) is:
0 = -20A
65536 = +20A

DACC = 32768 * (1 + Ic / 20)

Computed by current_to_dac()

Code
----


Loading…
Cancel
Save