Electronics > Beginners

Rigol DS1054Z 50 ohm setting.

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Mechatrommer:
Diy is good enough for 100MHz, probably up to 500MHz..

Gary350z:
I have a related question.
Say you have your scope connected to a 30VDC power rail with a coax or X1 probe, and you accidentally hit the 50 ohm impedance button. Now you have 0.6A (0.6A=30/50) going into the scope, and the scope is dissipating 18W (18W=30*30/50). I think this would damage the scope. Am i right, or am I missing something? It bothers me a lot that you could blow up your scope by accidentally pushing a single button.

Nitrousoxide:

--- Quote from: Gary350z on February 15, 2019, 02:14:26 pm ---I have a related question.
Say you have your scope connected to a 30VDC power rail with a coax or X1 probe, and you accidentally hit the 50 ohm impedance button. Now you have 0.6A (0.6A=30/50) going into the scope, and the scope is dissipating 18W (18W=30*30/50). I think this would damage the scope. Am i right, or am I missing something? It bothers me a lot that you could blow up your scope by accidentally pushing a single button.

--- End quote ---

Yep. Thats why most scopes that have, or are only 50 Ohm have a warning that says "Do not exceed 5Vrms". Because if you're DC coupled, you're going to have a very, very bad time. All that energy will be dissipated in the matching method they use (probably just a 50r resistor).

David Hess:

--- Quote from: Gary350z on February 15, 2019, 02:14:26 pm ---I have a related question.
Say you have your scope connected to a 30VDC power rail with a coax or X1 probe, and you accidentally hit the 50 ohm impedance button. Now you have 0.6A (0.6A=30/50) going into the scope, and the scope is dissipating 18W (18W=30*30/50). I think this would damage the scope. Am i right, or am I missing something? It bothers me a lot that you could blow up your scope by accidentally pushing a single button.
--- End quote ---

X1 probes can have considerable series resistance which is higher than 50 ohms but in general what you say is correct.  Well designed oscilloscopes monitor the input voltage level and disengage their internal 50 ohm termination if a dangerous overload is detected to protect their internal termination.

metrologist:

--- Quote from: ebastler on February 15, 2019, 05:55:26 am ---
--- Quote from: metrologist on February 15, 2019, 05:51:39 am ---I guess that is likely to be good enough for the application. I've made a few terminations using SMD resistors and a BNC connector.

--- End quote ---

Since you don't tell us what "the application" is, it's tough to comment on that statement.  :P

--- End quote ---

The topic context is about the OP and a DS1054Z. I'm  thinking that most use cases for this scope is likely not to be effected much by a poorly RF matched through termination. I don't typically make very sensitive measurements with my scope, though. I guess using a wire-wound resistor might cause problems? Could make one worse than serialing 25, 2W wire-wound resistors? That would look like a foot-long coil.

The terminations I made used 4 radially mounted SMD resistors and that application was for single port OSL reflectometer calibrations up to around 4 GHz. If I remember correctly, they performed very well when compared to a commercial calibration T from the German company. This is just for field level applications.

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