Probe on switching inductor - Page 1
Forum section: electronics / general

author: Lotus
author_rank: Contributor
timestamp: November 08, 2012, 08:50:14 pm
content: When an inductor swicthes off, there is a large voltage spike, can this in any way damage my Rigol oscilloscope?

author: LaurenceW
author_rank: Frequent Contributor
timestamp: November 08, 2012, 09:05:38 pm
content: You are going to have to give us a bit more than that, Lotus!What is your circuit? What rating is the inductor? What type of Scope probe were you using? Is your Rigol now suddenly dead? (In which case, you might have just answered your own original question).

author: Lotus
author_rank: Contributor
timestamp: November 08, 2012, 09:30:07 pm
content: My Rigol isnt deadBecause I havent measured voltage across the inductor/relay.I remember from school, that switching inductors (my relay going on/off) will generate a large voltage spike.Are those spikes dangerous when using like 12V?The probes are standard, and come with the scope from DX.I ask because I would expect an oscilloscope to be able to handle 'ooopses' like that

author: MartinX
author_rank: Regular Contributor
timestamp: November 08, 2012, 09:46:32 pm
content: If you always use the Rigol probe in the 10X setting the chances are greatly reduced that you damage the input of the scope, I think there would have to be quite a powerful spike to do real damage. But if you have a large inductor and high currents then there could easily be several kV generated and some current to back it up, you just have to do an assessment of what could be generated in the circuit you are about to connect the scope to.

author: tom66
author_rank: Super Contributor
timestamp: November 08, 2012, 10:11:23 pm
content: The Rigol has a transient rating of 1000Vpk on the inputs, so the occasional spike should not damage it.

author: amyk
author_rank: Super Contributor
timestamp: November 09, 2012, 06:32:40 am
content: Depends on the inductance and the dV/dt.

author: paudav
author_rank: Contributor
timestamp: November 10, 2012, 12:29:40 pm
content: Quote from: amyk on November 09, 2012, 06:32:40 amCan you elaborate on this? I don't see how Differential Calculus helps us evaluate the situation.I mean, aren't we just concerned with the peak voltage of the spike, here? Or maybe how long the spike spends over a certain threshold?-PBD

author: Achilles
author_rank: Regular Contributor
timestamp: November 10, 2012, 02:36:35 pm
content: hmmm, sounds crazy, but wouldn't there be a chance to catch the peak with a meter that has a peak hold or so. That could at least show in which ranges the voltage can be (if the peak-hold is fast enough). Well, meant as question for all around...out of curiosity.I would say that it makes a difference on your circuit..... what voltage or current is going through your coil, is it just the coil shut down or is there some capacitor or so to slow the shut-off-time down?EDIT:http://www.physics.unlv.edu/~bill/PHYS483/relay.pdfHere they give 20kV as value, but that's in automotive use and you have high current running through the relais. Therefore it could be seen like an old "contact driven ignition" system which just is just switching an contact to establish and break a current flow from the battery through the ignition coil (which is a transformer here).So I expect your voltage is lower, but don't know....as we don't know your circuit.