just learned about saturation the hard way:
i play with current measurement, CT N ( turns) and burden resistor and i run into that problem.
Background: for a given current transformer if the burden resistor is to high and the primary current to high
the CT goes into saturation. ( can find lots of references here too, but interesting to read www.idc-online.com/technical_references/pdfs/electrical_engineering/current_transformer_concepts.pdf )
Symtoms for CT in saturation:
- for calibrating EMON by a low current get a ICAL factor.
but when you test it with a high current need a ICAL factor twice or more
- when calibrating PhaseCAL to get p=1.0 with a OHM LOAD need high values ( 4..) instead the default 1.7
and that is how my arduino inputs looked like ( Ain range 0 .. 1023 for 0 .. 5V with 2V5 AC offset)
here i exceeded the prim. AC current (1.7A)
for the CT ( N = 1000 ) and used burden resistor (470ohm) measuring range is only about 1A.
Not read this then? http://openenergymonitor.org/emon/buildingblocks/report-yhdc-sct-013-000...
thanks, very good link.
only using arduino and no scope available it was very interesting for me to see that current plot.
as the CT is less 1$ i still think its worth the extra work.
a combination of range adjustment by burdenresistors
- one big soldered to CT ( low ampere range )
- one small parallel to it by jumper ( high ampere range )
+ using the trick to loop the primary current 2..3 times through the CT for increase sensitivity for low currents
gives many possible configurations.
but just lookout for that saturation trap.
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