# Current Limit in Oscilloscope?

#### riemanndiy

Joined Jul 25, 2020
5
Hello, newbie here. I always see there's a specification about the max Voltage, but not about current. I have a part of the circuit where I have 500mA, can I measure safely the voltage oscillation, with such "high current"? I don't want to cook my oscilloscope. Thank You

#### trebla

Joined Jun 29, 2019
283
To measure current with oscilloscope you must use current probe. If you can put a small resistor to the circuit then you can measure voltage drop on this resistor and calculate current with Ohms law: I=U/R. But usually added resistance distorts real current flow in the circuit and maybe also normal functioning this circuit.

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#### Ian Rogers

Joined Dec 12, 2012
845
Oscilloscopes don't really measure current... Its a voltage probe... You'll need to shunt the circuit to measure the voltage across the shunt, ergo the current..

#### dl324

Joined Mar 30, 2015
12,681
I have a part of the circuit where I have 500mA, can I measure safely the voltage oscillation, with such "high current"? I don't want to cook my oscilloscope.
Oscilloscopes don't measure current. They measure voltage and the input impedance is 1M-10M ohms to minimize circuit loading.

#### andrewmm

Joined Feb 25, 2011
1,140
Your scope is hopefully connected by a scope probe that has a 10 : 1 input attenuation.
The input of that is in the order of m ohm,
as such the current that flows into the scope is minimal / next to zero

If it was not, and your scope took say 1 mA, then measuring a voltage in a board would be affected by the current taken by the scope probe.

look at fig 5

NOW. You can normally switch your scope inpur to be 50 ohms to ground, in this case your not using a scope probe .
if you connect that to a voltage, you will take current, V = IR

if you connect the scope to say 100 V , then you will take 20 amps into the scope.
You will see the scope is rated for a power input on the inputs, so that you don't blow the input 50 Ohms.

#### bob91343

Joined May 29, 2019
16
Hello, newbie here. I always see there's a specification about the max Voltage, but not about current. I have a part of the circuit where I have 500mA, can I measure safely the voltage oscillation, with such "high current"? I don't want to cook my oscilloscope. Thank You
I have a current probe that is good to a few hundred Hz. It's an HP 428B with its own meter calibrated to 10A dc and a signal output that shows the wave. It's old but it works.