Re: Help interfacing Current Transformers to ADC


Joerg wrote:
beananimal wrote:

John Popelish wrote:

Yuriy K. wrote:

John Popelish wrote:


$6.50 @ qty.20 vs. CSE187L @ $2.34 @ 20 pcs.


Fair enough. What is the turns ratio and burden limit for these?


Google does wonders. :)

http://www.alliedelec.com/Images/Products/Datasheets/967-1100.pdf

Jameco P/N 627591
Mfg TRIAD MAGNETICS
Mfg # CSE187L
RoHS? No
In Stock Yes

10+ 1.81 it will be $36.20 per 20 pcs. Who can beat that?



%00to 1 ratio is quite practical for up to 30 amps (60 mA out). With
a 60 ohm half watt burden, that gives 3.6 volts RMS. I would want to
either use a Schottky bridge with something like a 50 ohm burden or a
silicon bridge with about a 39 ohm burden. Even though the output
does not take up the full 5 volt A/D range, it allows for a bit of
surge current without producing a ridiculous voltage.

Very nice, if 30 amps load current is large enough.


The largest loads will be

1) dual 150W magnetic MH ballast, so figure 450W draw during operation
and somewhat more than that due to the inrush when It powers on.
2) All of the pumps are less than 200W motors, and no more than 2 will
be on any given monitored outlet.
3) 500 watt heaters, 1 per monitored outlet.

So most of the stuff will be well less than 10A during operation,
inrush is a different story.


Inrush is usually handled by having a resistor of, say, several kohm
between the rectified and filtered output of your CT circuit and the AD
converter (or the uC if it has built-in ADC). Then a diode to the VCC
rail and another to GND (BAV99 is a nice dual diode for that). The
white-knuckle approach would be to let the internal substrate diodes
take care of things after that resistor, something that's done all the
time. Just don't exceed abs max values.

Now if the CT circuit output voltage spikes when a lamp or motor turns
on the spike is capped.

I would MUCH rather stick with through hole stuff. Those tiny SOT
packages are not something I enjoy working with.

So here is where we seem to be at:
Choosing between:

500:1 CT TRIAD CSE187L (cheaper)
-=OR=-
1000:1 AMVECO AC-1020 (better choice)

Then using the scematic provided by Jim (If this is what you guys are
still talking about)
http://analog-innovations.com/SED/CurrentTransformer.pdf

What are the specs I need to be looking for in the bridge?

Again using the provided schematic, the output of the OP-AMP (standard
LM-324) will go to through a single 2k resistor that is tied to the
input pin of my PIC micro. To be even safer, the net between the
output resistor and the PIC should be tied to VCC and GND via reverse
biased 1N4148 or similar general purpose diodes?

This leaves me with choosing component values for (from the provided
schematic) R1, R2 and C1. Something for which I may need help. But at
this point I need to ensure that I am on the same page as those who are
helping me. If this is the case, then I can begin to look at the
circuit and how the values are derived (so that I fully understand what
is going on).

Question: Assuming that I (we) get this all worked out. Will the
input pins of the PIC need any caps or other filters to keep them from
behaving in a strange manner when not being sampled? I have read that
this can be a problem with some uC A/D topologies, as well as Analog
multiplexors (a currnet spike on all of the inputs each time the active
input is switched to the next pin).

.

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