ScopeMeter 199C Current Measurement

[gerp124]

Hello and thanks in advance for any advice you can offer- I'm definitely feeling like an idiot.

I dabble in electronics, so there's a lot I don't know, but this one is driving me nuts:

How do you measure current with a Fluke 199C ScopeMeter via direct connection- without a clamping probe?

1) Since I've already tried, I hope it's possible, and if not, I hope I haven't damaged anything.

2) If it _is_ possible, then I think all I need to know is what sensitivity I should select.

Should this be obvious?

I did read the manual- it simply states that I should choose the correct sensitivity for my current probe.

Again, thanks for any reads/responses :-)

[noidea]

Any oscilloscope (scopemeter or not) can only measure voltage, when you connect a clamp probe to a scope input it still is measuring the voltage output from the clamp probe and depending on the setup scaling the mV output from the clamp to display the result it in Amps or milliamps. The scopemeters have the benefit of the isolated input channels making this a lot easier and safer if this relates to mains/line voltage, If you don't have a current clamp probe then it is still possible to measure current using a resistor in the circuit as a current shunt and using a channel of the scope to measure the volt drop across the shunt. Have a read of this Fluke scopemeter application note on power measurement for a bit more of an understanding, however the setup and scaling is going to depend on the resistance of the shunt and that is going to depend on what current you are trying to measure.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwjz6Pfqo9PfAhXEc94KHSmSD2UQFjAAegQIBxAC&url=https%3A%2F%2Fdam-assets.fluke.com%2Fs3fs-public%2F2140127_a_w.pdf&usg=AOvVaw3OdaRyNVUw51vNoBxP9bgQ

[mahi]

How do you measure current with a Fluke 199C ScopeMeter via direct connection- without a clamping probe?

1) Since I've already tried, I hope it's possible, and if not, I hope I haven't damaged anything.

See noidea's reply for more information how to measure current with an oscilloscope but to answer your question, no, you did not damage the ScopeMeter. Toggling between V(olt) and A(mpere) on the ScopeMeter only affects the displayed units and scale. Internally it's always measuring voltage. So the "current" you measured with the ScopeMeter was just the voltage multiplied by the set current clamp sensitivity.

[jeroen79]

The scopemeters have the benefit of the isolated input channels

They are isolated from the rest of the world but not from eachother.
Keep that in mind if you want to measure with 2 channels.

[SG-1]

You can make your own shunts using various lengths & gauge wire for low frequency work.  Look through the scope menu to get the various values it can use directly. 


Be careful to use a gauge size that will not change appreciably with temperature due to the electric current & keep them straight, no coiling, that will add inductance.

[noidea]

The scopemeters have the benefit of the isolated input channels

They are isolated from the rest of the world but not from eachother.
Keep that in mind if you want to measure with 2 channels.

Are you sure on that, the user manual for the 190 series one indicates otherwise and it was the main reason I bought one.

From chapter 8 page  93 of the user manual:
Measuring Using Independently Floating Isolated Inputs
The test tool has independently  floating isolated inputs. Each input section (A, B, External Trigger / DMM) has its own signal input and its own reference input. The reference input of each input section is electrically  isolated from the reference inputs of  the other input sections. The isolated input architecture makes the test tool about as versatile as having three  independent instruments. The advantages of having independently  floating isolated inputs are:
•  It allows  simultaneous measurement of independently floating signals.
•  Additional safety. Since the commons are not directly connected, the chance of causing short circuit when measuring multiple signals is greatly  reduced.
•  Additional safety. When measuring in systems with multiple grounds, the ground currents induced are kept to a minimum.

[malagas_on_fire]

There is a test setup for measuring power on fluke website which gets volts and amps :

https://dam-assets.fluke.com/s3fs-public/2140127_a_w.pdf

[dirtcooker]

The scopemeters have the benefit of the isolated input channels

They are isolated from the rest of the world but not from eachother.
Keep that in mind if you want to measure with 2 channels.

Are you sure on that, the user manual for the 190 series one indicates otherwise and it was the main reason I bought one.

From chapter 8 page  93 of the user manual:
Measuring Using Independently Floating Isolated Inputs
The test tool has independently  floating isolated inputs. Each input section (A, B, External Trigger / DMM) has its own signal input and its own reference input. The reference input of each input section is electrically  isolated from the reference inputs of  the other input sections. The isolated input architecture makes the test tool about as versatile as having three  independent instruments. The advantages of having independently  floating isolated inputs are:
•  It allows  simultaneous measurement of independently floating signals.
•  Additional safety. Since the commons are not directly connected, the chance of causing short circuit when measuring multiple signals is greatly  reduced.
•  Additional safety. When measuring in systems with multiple grounds, the ground currents induced are kept to a minimum.

Fluke 199c indeed has isolated inputs (to 1Kv) and is my goto scope because of that and the CAT III 600v rating. Measured conductivity between probe grounds is 0.02 nS (50 gigohm) using a brymen 869. You can for example measure the input side of an offline switcher while probing the secondary side or anywhere else with the other scope channel or DMM with no worries. I also have a Fluke 123 which does NOT have inputs isolated from each other unfortunately.