My understanding of the scope inputs was that they are isolated, (-) independant from each other, and not even connected to ground. I was expecting that the scope measures the potential difference between (+) and (-). As it doesn't I will have to use a differential probe.
Differential probe is just safest, and in fact easier to understand, as I just want to measure the potential difference. It's a shame scopes aren't designed like that by default.
Here is a stupid question: If you always have to connect the tip to ground, as your (-) at the scope side is connected to ground, why do you need the tip at all, as you are always measuring the potential difference between your signal and ground, and the scope is connected to ground already?
I actually have seen once someone measuring with a scope, and he did not connect the tip. I found it rather funny, and was pointing out that he is measuring a potential difference, and therefore needs to connect both. But from the conclusions in this posting, my view on reality was wrong, as the scope seems to measure always referenced to ground. So now I am actually in doubt myself, and believe that the guy doing this measurement without tip, might not have been an idiot after all, or do I miss out something here =)
Using the ground clip to measure mains is a big NO NO. You'll be lucky if the only thing damaged is your scope.
Ground is earth, not minus and not negative.
Also it's AC so there is no minus. And even if English is not your language, minus means the same as in English and it's not ground/Earth.
Using the ground clip to measure mains is a big NO NO. You'll be lucky if the only thing damaged is your scope.
Almost certainly didn't break anything.
All the current flowed through your BNC shield connectors on the front, and that would have been limited by the series resistor on top.
Unless you are dealing with a massively high powered system, your scope will be fine.
Okey, then I have to look for another device.
I was planning to use this as an isolated front-end, to make sure that the clip on the probe is floating, and not connected to ground.
I want to have a system where I can connect the probe tip and clip to any point in my electronic design, without any risk of making a short circuit. I want to make an objective measurement of the potential difference between the two measure points (the tip and the clip), without affecting the signals in my electronic design, and without affecting the functionality of my scope.
If I understand well, this device from Siglent does it, but at same time provides attenuation, and limits the bandwidth to 1 MHz (at least does not affect signal characteristics below 1 MHz).
What I am looking for is basically the same device, but without the attenuation and without affecting the bandwidth. Just the isolation of the input signals, to make sure that the clip of my probe can not cause a short circuit.
Basically I am looking for an adapter (similar form factor as the Siglent adapter) which turns the standard Rigol probe (as delivered with the scope) into a differential probe, when I put it in between my scope and my probe. Does such an adapter exist?
I want to use my standard Rigol probe as a differential probe, where I can connect the tip and the clip to any measure point without causing a short circuit. This should even apply when measuring with the 2 channels at the same time. I want that the clip of probe 1 is independant of the clip of probe 2.
You will have 4 options.
Buy an isolated input DSO.
Buy differential probes.
Buy a 4 Ch scope and use std probes without Reference(Gnd) clips for a 2 Ch result
Forget the idea and learn how to use a scope safely.
Using the ground clip to measure mains is a big NO NO. You'll be lucky if the only thing damaged is your scope.
Using the ground clip to measure mains is a big NO NO. You'll be lucky if the only thing damaged is your scope.
Why? You might burn the ground clip I guess, but the rest of the path to ground should be chunky enough to survive till the fuse blows. The ground getting raised a bit shouldn't affect the circuitry either AFAICS.
The current return path is via the GND tracks on the scope PCB.
Using the ground clip to measure mains is a big NO NO. You'll be lucky if the only thing damaged is your scope.
Why? You might burn the ground clip I guess, but the rest of the path to ground should be chunky enough to survive till the fuse blows. The ground getting raised a bit shouldn't affect the circuitry either AFAICS.
Option 2) Where to get affordable/qualitative/reliable differential probe for MSO2072A?
Option 3) Do you mean that you then will use the tips only and use math operations from the scope to combine tip1 and tip2 for the 1st channel, and tip3 and tip4 for the 2nd channel? Nice suggestion actually.
Please forgive my asking a question in someone else's thread, but it seems related to the discussion. If this is poor form, just tell me I'm new to all this, just got my first scope, and will watch/read the items linked in post #2.
In the first post, Rene was measuring across 2 resistors.
I'd like to measure the voltage drop across a current shunt (to figure out the current), with a 2 channel scope. So a similar situation, but just one resistor. The circuit is battery powered, so the scope and circuit both being grounded shouldn't be an issue.
- I believe I could use the tip of the two channels, one before the shunt, one after. Then subtract one from the other to figure out the voltage drop across it. But using both channels feels like it might make things less accurate? At most, the drop across it should be 75mV, so fairly small.
- As the circuit is battery powered, could I put the tip of channel 1 before the shunt, and the clip of channel 1 after it? Thereby measuring the voltage drop "directly" with a single channel? I wouldn't be able to use channel 2 for anything, I assume, as that might cause a reference voltage difference problem.
Thank you.
The current return path is via the GND tracks on the scope PCB.
Isn't the BNC simply soldered to the ground plane, which is connected to the chassis at each standoff?
You will have 4 options.
Buy an isolated input DSO.
Buy differential probes.
Buy a 4 Ch scope and use std probes without Reference(Gnd) clips for a 2 Ch result
Forget the idea and learn how to use a scope safely.
Regarding the proposed options:
Option 1) Not an option, I want to stick with MSO2072A
Option 2) Where to get affordable/qualitative/reliable differential probe for MSO2072A?
Option 3) Do you mean that you then will use the tips only and use math operations from the scope to combine tip1 and tip2 for the 1st channel, and tip3 and tip4 for the 2nd channel? Nice suggestion actually.
Option 4) Even if you know what you are doing, you might make mistakes (e.g. on a Monday morning)
You will have 4 options.
Buy an isolated input DSO.
Buy differential probes.
Buy a 4 Ch scope and use std probes without Reference(Gnd) clips for a 2 Ch result
Forget the idea and learn how to use a scope safely.
Regarding the proposed options:
Option 1) Not an option, I want to stick with MSO2072A
Option 2) Where to get affordable/qualitative/reliable differential probe for MSO2072A?
Option 3) Do you mean that you then will use the tips only and use math operations from the scope to combine tip1 and tip2 for the 1st channel, and tip3 and tip4 for the 2nd channel? Nice suggestion actually.
Option 4) Even if you know what you are doing, you might make mistakes (e.g. on a Monday morning)
Option 4) Even if you know what you are doing, you might make mistakes (e.g. on a Monday morning)
Why is it so expensive? Are all differential probes in this price range?
Is it because of the high voltage levels or because of the bandwidth?
That sounds like the sort of job multimeters are designed for, but both methods will work fine. Beware that oscilloscopes are intended for accurate display of waveforms and not accurate reading of voltages and so their accuracy in this situation kind of sucks. It'll be close, but don't expect a better reading than a multimeter. The DS2072, for example, specs its DC gain accuracy at 2% full scale compared to 0.05% for a Fluke 87.
That sounds like the sort of job multimeters are designed for, but both methods will work fine. Beware that oscilloscopes are intended for accurate display of waveforms and not accurate reading of voltages and so their accuracy in this situation kind of sucks. It'll be close, but don't expect a better reading than a multimeter. The DS2072, for example, specs its DC gain accuracy at 2% full scale compared to 0.05% for a Fluke 87.
Thank you for the reply, I appreciate it.
Sorry, I didn't mention that I'm looking to measure current spikes as servos start to move. So I'm looking to measure a very brief event, likely too quick for a multimeter to capture. But a scope should show it.
My thought was to try putting a multimeter across the shunt, along with the scope, and flow a known, constant current through it. Letting me get some sense of "calibration" for the scope's reading, vs a multimeter. Not a perfect solution, but I'm trying to do the best I can with the tools I have access to.