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Registered Member #2731
Joined: Thu Mar 11 2010, 05:48AM
Location:
Posts: 4
Hi,
Some people use a shunt measurement device. However, can one use a clamp current meter with an oscilloscope? The only reason one might not is because of the induction caused by a fast raising current.
I'd like to see the current curve when firing my coilgun. Is that possible? Should I use a shunt or a clamp?
Registered Member #2731
Joined: Thu Mar 11 2010, 05:48AM
Location:
Posts: 4
I intended to use a shunt, but it is written on wikipedia that it is not good for high voltages.
If the current being measured is also at a high voltage potential this voltage will be present in the connecting leads to and in the reading instrument itself. Sometimes, the shunt is inserted in the return leg (grounded side) to avoid this problem. Some alternatives to shunts can provide isolation from the high voltage by not directly connecting the meter to the high voltage circuit. Examples of devices that can provide this isolation are Hall effect current sensors and current transformers (see clamp meters).
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
1. Wikipedia is not a generally dependable reference for technical topics, but appears to be doing OK on this one today.
2. If your current shunt is on the low side of the circuit, no high voltages are presented to the 'scope. But the shunt's own inductance, and inductance of wire between the shunt and "ground", significantly complicate the picture when fast-rising currents are involved.
What current magnitude and pulse width do you expect in your coil gun application? Can you show us a schematic?
3. Clip-on inductive current probes, if designed for appropriately high frequency, are a good bet for your application. Once again, you need an idea of current magnitude and pulse width before we can get serious about instrumentation choices.
Registered Member #347
Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106
You should be able to use a current transformer as used in a DRSSTC to measure primary current. Two cascaded 32:1 CTs will produce a ~1000:1 current ratio. Terminate that into a 1Ohm resistor, and you'll have an isolated sensor that produces 1mV/Amp. I'm not sure weather or not it'll saturate with the current pulse in a coil gun application, but it should be obvious (a sudden drop in the reading).
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Current sensor
