current waveforms

[Deleted]

Gary can you help me understand how to view current waveforms on the oscilliscope ?

[Gary Lecomte]

Your Question is to Vague.

But there is a bit of some oscilloscope waveforms on my projects page, that may help a bit.

[Deleted]

By definition, V=IR. The Oscilloscope , The most valuable machine for education of engineers.
Voltage looks like Current with a phase difference if inductance or capacitance is within
the circuit. Resonance is when Voltage looks just like current with no phase shift.
Resonance is when the phase of an inductor cancels the phase shift of a capacitor.
Pure resistance has no effect on phase shift nor a contribution to current looking different
than voltage. Pure resistance does not exist. However, one can purchase resistors
with minimized phase shift. To view current waveforms one takes the series flow and shows
it on an oscilloscope,without overload. That is one breaks the wire--"option below"-- and inserts the oscilloscope
in line. Once the oscilloscope is in line, the current is shown. The interesting part is to have
two channel input and to connect channel B across a resistor . One can now see the
phase and amplitude diff. between voltage and current. One can change the freq. of operation
and find resonant frequencies and watch the current amplitude and phase change.
The result to learn from this experiment is to define ones amplitude and phase response
or using the broad term " bandwidth" of a circuit or even the true performance of a filter.
Basically an engineer will find out if the circuit is going to work for the need intended.
Also one can find the output and input impedance of a circuit by watching the
3db loss points of voltage and current along with phase shift.
If you cannot do an inline insertion of the scope, hook one channel of the scope
to an inductor or a small capacitor. You can now subtract or add the 90 degree phase
shift of the inductor or capacitor and with good scopes one can display the current
with the phase shift subtracted. In critical circuits for power loss in resistors , inductors and capacitors
one can find the exact phase shift taking place in all components and determine if the loss
is acceptable. Any phase difference between voltage and current means a loss in power
transfer. Most circuits we deal with , this is really not going to be of concern as for as power
loss is related compared to the more important big question. Does the circuit work good enough to do what was needed? Perfection can be your enemy or somtimes not.

[Deleted]

I've found very little information how to use the resistor method in terms of being careful with my oscilliscope.The current for one paticular project will be near 20 amps.
The information you posted is more than anything Ive been able to read, Thank You very much.

[Gary Lecomte]

kevins said:

I've found very little information how to use the resistor method in terms of being careful with my oscilliscope.The current for one paticular project will be near 20 amps.
The information you posted is more than anything Ive been able to read, Thank You very much.

A Very Small Resistor is All that is Needed. Less than 1 Ohm.
For your Situation, You can even use a 25 Amp Fuse instead of a Resistor.
Than connect your scope leads across it.

If your dealing with Live 110 or 220 AC Voltages, Be aware that your Oscilloscope is usually Grounded, so you need to put the fuse (Resistor) in the Neutral wire for testing this.

[Deleted]

Thank you again.
The purpose in my situation for viewing the current waveforms is for an electrolyser that operates from triangle current waveform.I need to see the current for that reason to build the appropiate input waveform generator.

[Gary Lecomte]

Unless your using an Inductor, I doubt your waveform we will change much.