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Ted Edwards
 
Posts: n/a
Default SCFM vs. CFM, also air flow/pressure across a regulator

Also e-mailed due an ISP suffering Altsheimer's:

Loren Coe wrote:

does anyone have a suggestion as to how i measure this with
just "normal" equipment, including an O'scope? running back
and forth to the utility co.power meter doesn't seem like a
very good approach.


If your scope is dual trace, you can do what you want with a current
transformer. You need a 120V to 12V transformer rated for a dozen or so
amps. Connect a 10 Ohm, 10 Watt resistor across the 120V winding.
Connect the 12V winding in series with a motor lead. The "backwards"
transformer will have 11A flowing in the "12V" winding which will become
1.1A in the "120V" winding. 1.1A in a 10 ohm resistor is 11 volts so
the other winding (the "12V" winding) will drop only 1.1V. This will
have negligable effect on the motor operation. If you now pick up the
hot motor lead in one channel of the scope and the secondary of the
current transformer in the other channel, you can measure the time
difference between the waveforms and calculate the phase shift.

Ted