I am a new owner of a Rigol DS1054Z scope and a BK Precision 4003A function generator. I am working on learning how to use these instruments without damaging the equipment or myself.
1) Should I purchase an isolation transformer to plug the DUT into?
2) Should I purchase a differential probe setup
2a) Can I use the differential probe set for ALL of my measurements?
3) Should I do both 1 & 2 of the above?
4) Finally, I have built some of my equipment with the audio bus grounded through a pair of diodes, a capacitor and a 5 ohm resistor. Does this arrangement change how I should measure/ground things.
In addition to the usual measuring of low voltage stuff, I would also like to look at PSU ripple of my tube equipment.
TIA
1) Should I purchase an isolation transformer to plug the DUT into?
2) Should I purchase a differential probe setup
2a) Can I use the differential probe set for ALL of my measurements?
3) Should I do both 1 & 2 of the above?
4) Finally, I have built some of my equipment with the audio bus grounded through a pair of diodes, a capacitor and a 5 ohm resistor. Does this arrangement change how I should measure/ground things.
In addition to the usual measuring of low voltage stuff, I would also like to look at PSU ripple of my tube equipment.
TIA
There are many dangers:
- if you use an isolation transformer for the DUT and ground some arbitrary point in the DUT with the scope ground lead you may end up with the exposed metal case of the DUT being at a lethal voltage.
- if you isolate the scope then the scope exposed metal (including the BNC connectors) will enjoy the same potential of what it is connected to.
-if you use differential mode with the probe ground connected to DUT ground you will be safe but there is a limit to the differential withstand voltage capability of the scope input circuitry.
In my experience the safest option is DUT isolation but only when needed and combined with a dim lamp test device that has a push button ON switch so that the DUT is only powered when at least one hand is out of harm's way. That way, if there is an accident you will hopefully not get a zap through your heart.
- if you use an isolation transformer for the DUT and ground some arbitrary point in the DUT with the scope ground lead you may end up with the exposed metal case of the DUT being at a lethal voltage.
- if you isolate the scope then the scope exposed metal (including the BNC connectors) will enjoy the same potential of what it is connected to.
-if you use differential mode with the probe ground connected to DUT ground you will be safe but there is a limit to the differential withstand voltage capability of the scope input circuitry.
In my experience the safest option is DUT isolation but only when needed and combined with a dim lamp test device that has a push button ON switch so that the DUT is only powered when at least one hand is out of harm's way. That way, if there is an accident you will hopefully not get a zap through your heart.
"if you use differential mode with the probe ground connected to DUT ground you will be safe
but there is a limit to the differential withstand voltage capability of the scope input circuitry."
Differential voltage probes don't have a DUT ground connection, just the output BNC connector to the scope.
but there is a limit to the differential withstand voltage capability of the scope input circuitry."
Differential voltage probes don't have a DUT ground connection, just the output BNC connector to the scope.
Blueglow Electronics has a series of youtube videos on using a scope for audio use. He just finished part 4B, push-pull tube amp diagnosis. The first three are on how to use the scope. Since he is using the same instruments as you, I would recommend taking a look, they run 30 - 45 minutes each.
A safe approach is not to touch anything when powered on, even the scope.
A nuisance if you want to move probe around or change the scope settings but better safe than sorry.
Some IC's are touchy about attaching scope probe while powered up and can blow up.
I blew up a couple of irs2092's before I realised what was going on.
A nuisance if you want to move probe around or change the scope settings but better safe than sorry.
Some IC's are touchy about attaching scope probe while powered up and can blow up.
I blew up a couple of irs2092's before I realised what was going on.
Any differential probe I've ever worked with has had a ground connection that established the common-mode voltage for the probe. You had to obey both the differential mode and common mode maxima for voltage.
That said, the probes were fairly high frequency probes (a few GHz if I recall correctly), which could make a difference.
I use two regular probes when making differential measurements. Connect one to each channel and have the scope display CH1-CH2.
Tom
Many of them do have a ground connection for the reasons Tom mentioned. Especially low voltage diff probes.
N2752A InfiniiMode 6 GHz Active Differential Probe | Keysight
Note the 3rd pins of the solder-in and pin header tips.
You're right that I have never seen one on those HV style probes, probably because they have huge divider ratios. I've always seen it on isolated probes like Teledyne LeCroy HVFO-108 where there is optical isolation.
N2752A InfiniiMode 6 GHz Active Differential Probe | Keysight
Note the 3rd pins of the solder-in and pin header tips.
You're right that I have never seen one on those HV style probes, probably because they have huge divider ratios. I've always seen it on isolated probes like Teledyne LeCroy HVFO-108 where there is optical isolation.
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In my opinion, a good differential or isolated probe is the best way, but it can get expensive. It's unlikely you can use one probe for all of your measurements due to the different characteristics, but it depends on what you are doing.
Sapphire makes the majority of mid-range HV diff probes for other OEMs, you can look into them. There is a lot of good info on the EEVBlog forum.
I believe I'm going to go with the differential probe and not the isolation transformer. The cost will not be too much higher and the whole "shebang" seems less Rube Goldberg to me. The inexpensive unit from Micsig DP10013 is inexpensive enough to experiment with. Could someone address the issue of the ground lifter circuit I asked about? Would that have caused a problem in measuring?
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this family of probes:
TA041 25 MHz active differential oscilloscope probe
is good for audio work, very useful to not have to worry about grounding so much. They are some china OEM design so you can find them under different brands at different prices. They run through battries pretty quickly but you can buy a wall adapter cheaply. Active probes HV diff probes are the best and safest way, I avoid repositioning when circuits are powered.
TA041 25 MHz active differential oscilloscope probe
is good for audio work, very useful to not have to worry about grounding so much. They are some china OEM design so you can find them under different brands at different prices. They run through battries pretty quickly but you can buy a wall adapter cheaply. Active probes HV diff probes are the best and safest way, I avoid repositioning when circuits are powered.
How often do you work on audio equipment without a 3-wire AC plug? If, say, an amplifier has a 3-wire cord, with safety ground connected to chassis and the scope's 3-wire AC cord is plugged into the same strip, you should be able to use normal probes in the normal way to measure power supply ripple. Safely.
The problem is when you decide, for some reason, you want to see the voltage drop across the inductor in your pi-filter. Obviously you cant connect the scope probe across the inductor, so you need a differential probe in this case. It's for these "floating" measurements that the diff probe is typically used.
You can "float the scope" but the idea is frowned on - even though many scopes are built to be able to do this. We had a battery powered Tek scope that came with all kinds of warnings - they wanted you to ground it, even when using battery power. So what's the battery for?
I was measuring noise on a 3.3V powersupply with the scope completely isolated from ground - including RS-232 communications with it. Tek wouldnt budge and I had to abandon the measurement scheme, due to intra-corporate "safety" reasons. 3.3V, earth grounded at the measurement point, floating scope which was a no-no with them officially.
How many voltage drop across components with both ends raised a few hundred volts above ground do you really need to make?
Another useful trick is to have a current probe / transformer on hand. These usually connect in a electrically isolated way, with less potential harm possibility than making electrical contact to a high voltage. Measure the current through the inductor, instead of the voltage across it - if that suits what you're interested in seeing.
I have a Fluke "ScopeMeter" - battery powered - that I use in the same way as my DMM. It has no issue making a floating measurement, same way as I'd have no issue putting the two DMM probes across that inductor. I'd sell it and go for a Rigol, if it didnt have this singular benefit that I might want to use someday.
Tektronix would have a cow -
The problem is when you decide, for some reason, you want to see the voltage drop across the inductor in your pi-filter. Obviously you cant connect the scope probe across the inductor, so you need a differential probe in this case. It's for these "floating" measurements that the diff probe is typically used.
You can "float the scope" but the idea is frowned on - even though many scopes are built to be able to do this. We had a battery powered Tek scope that came with all kinds of warnings - they wanted you to ground it, even when using battery power. So what's the battery for?
I was measuring noise on a 3.3V powersupply with the scope completely isolated from ground - including RS-232 communications with it. Tek wouldnt budge and I had to abandon the measurement scheme, due to intra-corporate "safety" reasons. 3.3V, earth grounded at the measurement point, floating scope which was a no-no with them officially.
How many voltage drop across components with both ends raised a few hundred volts above ground do you really need to make?
Another useful trick is to have a current probe / transformer on hand. These usually connect in a electrically isolated way, with less potential harm possibility than making electrical contact to a high voltage. Measure the current through the inductor, instead of the voltage across it - if that suits what you're interested in seeing.
I have a Fluke "ScopeMeter" - battery powered - that I use in the same way as my DMM. It has no issue making a floating measurement, same way as I'd have no issue putting the two DMM probes across that inductor. I'd sell it and go for a Rigol, if it didnt have this singular benefit that I might want to use someday.
Tektronix would have a cow -
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Well, I received my differential probe last evening and tried a few measurements from my BK 4003a generator. I can't make sense of the channel two trace which is from the differential probe. I am running both probes directly from the SG and the channels are set appropriately I believe (10X and 50X). Any ideas why my trace is useless?
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Wild stabs in dark---
Would you provide a sketch of your probe(s) and generator setup, including any ground clip connections?
I note that Ch 2 is inverted re Ch1; is it possible that the two inputs of the differential probe are responsible for the inversion? ie Plus input on ground and minus input to generator output? If you exchange the differential probe connections, does the displayed polarity flip? Can you capture a single sweep? Does that provide insight? (I'm imagining a family of successive sweeps with hum overlaying.)
Would you provide a sketch of your probe(s) and generator setup, including any ground clip connections?
I note that Ch 2 is inverted re Ch1; is it possible that the two inputs of the differential probe are responsible for the inversion? ie Plus input on ground and minus input to generator output? If you exchange the differential probe connections, does the displayed polarity flip? Can you capture a single sweep? Does that provide insight? (I'm imagining a family of successive sweeps with hum overlaying.)
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