iIs the uCurrent Gold isolated? - Page 1
Forum section: electronics / testgear

author: m3g4by73
author_rank: Contributor
timestamp: November 26, 2017, 10:42:41 pm
content: I'd like to hook up my uCurrent to my Oscilloscope to measure current while also monitoring signals and voltages from my circuit.All my oscilloscope's GND probes are connected.Am I going to have shorts if the uCurrent is measuring current through my positive supply rail? I.e. Its "Current Inputs" are spliced into my +ve supply rail, or is its output floating with respect to its inputs?

author: SparkyFX
author_rank: Frequent Contributor
timestamp: November 26, 2017, 11:10:18 pm
content: Schematicsare linked on its project page, they show direct connection between the input and output on one rail.The thing with oscilloscopes is, all GNDs are connected and permanently connected to earth over its mains input (if it has one and does not run on battery or is not connected to earth in any other way).The µCurrent is a battery powered device and itself floating in regards to earth, as long as you keep it isolated. But once you connect oscilloscope GND to be able to see a signal, you ground that point in the circuit to earth. Think twice and measure if you work with non-isolated power supplies and such, it might be irrelevant if the power supply of your circuit is isolated or battery powered. It might also make sense to take chargers into consideration if it´s a device with a charger. You should safely measure these things before making a connection.Every time you need to measure between points of which both are not connected to earth, you need a differential probe that is isolated. Some people make the scope floating by isolating its earth connection, but this is usually disregarded, because all BNC outer connectors will carry the voltage the probes ground is connected to. If it´s mains voltage that can end deadly just by touching it. Should the scope not have the proper isolation against the voltages in the system it might be damaged as well.So you should really know what you are doing and use the proper tools for the job - either by using an isolated bench power supply that allows the point connected to ground and not connecting other scope inputs to a different point/having all other connections either open or use a differential probe.

author: EEVblog
author_rank: Unknown
timestamp: November 26, 2017, 11:56:07 pm
content: Quote from: m3g4by73 on November 26, 2017, 10:42:41 pmOnce you connect your oscilloscope then the uCurrent input is no longer floating.

author: m3g4by73
author_rank: Contributor
timestamp: November 27, 2017, 03:30:48 am
content: Thanks, the schematics helped a lot and show that the -In and -Out are connected.My circuit under test is running off batteries so there's nothing particularly dangerous going on.I'll just be sure to put the uCurrent on the battery's -ve terminal in future so I can use my other oscilloscope channels to measure GND referenced voltages at the same time.

author: texaspyro
author_rank: Super Contributor
timestamp: November 27, 2017, 04:56:03 am
content: Quote from: SparkyFX on November 26, 2017, 11:10:18 pmOr use a scope with isolated / floating inputs... Tek THS7xx portable / battery operated scopes for the win! My THS730A seems to be my go-to scope for most tasks not requiring anything fancy.

author: SparkyFX
author_rank: Frequent Contributor
timestamp: November 27, 2017, 05:26:58 pm
content: Right, i forgot about them, anyway, several channels might be connected. The Fluke 105B i got here at work has both channel grounds interconnected. Then there is also scopes with differential input only, completely safe for that matter.So there is no right or wrong answer for all scopes and all combinations, but its up to you to check what you have in front of you before making mistakes.