sampling with BS2SX
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Hi all,
I am using a 115 VAC induction motor. I need to digitize the motor's
voltage and current waveforms and then serially send them to a PC for
analysis. The data will be collected over a 3-4 second interval as the
motor accelerates from locked rotor to no-load. I plan to use a
step-down transformer (for the voltage) and a hall-effect sensor (for the
current) to obtain representions of the waveforms that can be sent to
separate channels on a 12 bit A/D converter. I would like to sample both
waveforms as many times per second as possible (synchonized by a
comparator at the zero crossings of the voltage waveform) to hopefully
obtain a Nyquist rate high enough to accurately portray at least the 5th
harmonic of a 60Hz waveform. The digitized results will be stored in an
EEPROM until some later time a VB program on a PC will poll the stamp
for the data so it can stuff it into a database suitable for graphing in
Excel. Does this rate of sampling,writing to EEPROM, etc. seem doable
for a BS2SX? Any comments, concerns, suggestions, questions, etc.
appreciated...
Also, does anyone know of where I can get a manual for a BK Precision,
model 1590, 100 MHz scope? If it is not in violation of any copyrights,
etc, I would even consider purchasing a manual that has been photocopied.
As this portion of the post is OT, please respond to this off-list.
Thanks,
Aaron
I am using a 115 VAC induction motor. I need to digitize the motor's
voltage and current waveforms and then serially send them to a PC for
analysis. The data will be collected over a 3-4 second interval as the
motor accelerates from locked rotor to no-load. I plan to use a
step-down transformer (for the voltage) and a hall-effect sensor (for the
current) to obtain representions of the waveforms that can be sent to
separate channels on a 12 bit A/D converter. I would like to sample both
waveforms as many times per second as possible (synchonized by a
comparator at the zero crossings of the voltage waveform) to hopefully
obtain a Nyquist rate high enough to accurately portray at least the 5th
harmonic of a 60Hz waveform. The digitized results will be stored in an
EEPROM until some later time a VB program on a PC will poll the stamp
for the data so it can stuff it into a database suitable for graphing in
Excel. Does this rate of sampling,writing to EEPROM, etc. seem doable
for a BS2SX? Any comments, concerns, suggestions, questions, etc.
appreciated...
Also, does anyone know of where I can get a manual for a BK Precision,
model 1590, 100 MHz scope? If it is not in violation of any copyrights,
etc, I would even consider purchasing a manual that has been photocopied.
As this portion of the post is OT, please respond to this off-list.
Thanks,
Aaron
Comments
The eeprom is the limiting step in your scheme to capture the voltage and
current waveforms from a motor. At 5 to 10 milliseconds for a write, the
sampling frequency is already limited to less than 200 hertz.
You said you want to, "obtain a Nyquist rate high enough to accurately
portray at least the 5th
harmonic of a 60Hz waveform". That means the sampling frequency should be,
say, 1000 hz. That is a tall order for even a BS2SX. One millisecond to
capture both samples and put them somewhere, plus overhead. But the BS2SX
can only execute about 10 instructions in that time interval. Not to say
that it couldn't be done. But the code and the hardware would have to be
very tight.
On the analog side, I think there would not be much energy in the fifth
harmonic anyway. (Someone who knows more about motors might correct me on
that one.) I think most of the story for an induction motor will be in the
phase relation between voltage and current at 60 hz. The step-down
transformer you propose to monitor the voltage across the motor is not a
good idea; it will introduce phase shifts of its own.
You also asked about a source for manuals for your B&K scope. I recently
and happily purchased a user/service manual for a Leader 'scope from:
http://www.manualsplus.com
Manuals Plus
130 North Cutler Drive
North Salt Lake, UT 84054
1-801-936-7000 Voice
1-801-936-7004 Fax
Mon-Fri 8:00AM-5:00PM Mountain Time
regards,
Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com