Products > Test Equipment
Floating Scopes
tautech:
--- Quote from: PA4TIM on June 23, 2017, 11:27:36 am ---I'm just in the middle of a review and teardown of an isolated Siglent portable scope.
--- End quote ---
Of which I've pushed and pushed for the front end to be incorporated into a good basic benchtop DSO.
Manufacturers just don't get it do they ? :rant: :horse: :-//
Maybe they're waiting till I push off this life so they don't have to call it their Tautech model. :-DD
Shock:
I think I may have mentioned this in another thread previously. But lets take the Rigol DS1000Z series manual as an example:
--- Quote ---Ground The Instrument.
The instrument is grounded through the Protective Earth lead of the power cord. To avoid electric shock, it is essential to connect the earth terminal of power cord to the Protective Earth terminal before any inputs or outputs.
--- End quote ---
--- Quote ---DS1000Z series digital oscilloscopes can make measurements in Measurement Category I.
WARNING This oscilloscope can only be used for measurements within its specified measurement categories.
Measurement category I is for measurements performed on circuits not directly connected to MAINS. Examples are measurements on circuits not derived from MAINS, and specially protected (internal) MAINS derived circuits. In the latter case,
transient stresses are variable; for that reason, the transient withstand capability of
the equipment is made known to the user.
--- End quote ---
These go a bit further than the "don't put the plastic bag on your head" type warnings.
There are a few oscilloscopes around are designed for direct mains voltages, HV and channel isolation. However the majority of modern oscilloscopes are not, so you have use them in a safe manner and within the conditions they were designed for to achieve your desired measurement and preserve the integrity of the instrument.
Tektronix Floating Measurements Selection Guide.
--- Quote ---Fortunately, there are solutions available which are not only safe but much more accurate than the extremely dangerous and unacceptable procedure of floating your oscilloscope. These fall into general categories: differential probes, isolated input oscilloscopes, isolation transformers and isolation amplifiers.
--- End quote ---
As with all equipment using it unintended way can cause unpredictable results.
Tektronix Floating an Oscilloscope: A Definition
--- Quote ---“Floating” a ground-referenced oscilloscope is the technique of defeating the oscilloscope’s protective grounding system disconnecting “signal common” from earth, by either defeating the grounding system or using an isolation transformer. This technique allows accessible parts of the instrument such as chassis, cabinet, and connectors to assume the potential of the probe ground lead connection point. This technique is dangerous, not only from the standpoint of elevated voltages present on the oscilloscope (a shock hazard to the operator), but also due to cumulative stresses on the oscilloscope’s power transformer insulation. This stress may not cause immediate failure, but may lead to future dangerous failures (a shock and fire hazard), even after returning the oscilloscope to properly grounded operation. Not only is floating a ground-referenced oscilloscope dangerous, but the measurements are often inaccurate. This potential inaccuracy results from the total capacitance of the oscilloscope chassis being directly connected to the circuit-under-test at the point where the ground lead is connected
--- End quote ---
So there it is, you could argue that you can increase the safety margin, but bypassing the protective ground/earth on oscilloscopes is inherently unsafe and avoidable to start with.
HighVoltage:
Tektronix made the handheld THS720P and similar model scopes with two channels.
Totally isolated from ground and from each other !
These scopes are pretty cheap these days, sometimes cheaper than a good differential probe.
Perfect for this kind of repair.
serggio:
Apart from dangerous use, regular scopes in "floating mode" can be very sensitive to noises.
This scopes and many probes too was not developed for using without ground connection.
If you doing measuring small differential signals, it can become problem. Your signal on scope screen can be affected by noise.
Electro Detective:
Whatever methods used to prod safely, I'll take my chances using a floating (if required) or fully earth/grounded isolating transformer powering the test gear,
rather than have the full force of the power station going through the DUT and oscilloscope in the event of ANY fault.
FWIW a GFCI/RCD or better still an RCBO, WILL WORK on the secondary side of a fully earth/grounded isolating transformer (or 'medical' transformer) so you've got some safety factor as well as isolation from the mains
If some people don't get that, or don't want to, then by all means ground yourself good and proper 100%
and good luck praying the GFCI/RCD and MCBs both work when SHTF, even when using clever probe$
oh, have you tested your GFCI/RCD lately ? once a month? will it still trip as it should? Are you sure?
The TEST button worked, and that's good enough ? LOL, good for you :clap:
Please :palm: :palm:
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