janneman,
If SY is to freeky on safety, why has he never suggested a Residual current operated circuit breaker? They take care of just about every worry he has.
Furthermore, you canot ever avoid dangerous voltages when it's a mains powered thing (unless you keep your hands out of the EUT).
In some cases, an incorrect "precaution" grounding can expose the user of greater hazard than a floating thing. (i.e. the symmetric power supply, which - despite all grounding precutions - can present a danger, even on the secondary side.)
An insulating (isolating?) transformer, again to break ground-relative potential hazards, can be another way to lower the risk.
It should be obvious to everyone that mains powered things can be dangerous. This is also the reason why most "providers" like Rod Elliot have several warnings on their sites and material. One can only warn and call for reason. An example (from real life): A scooter (motorcycle) manufacturer has to specifically state on a warning, that this bike contains no parts suitable for eating. It should be obvious to most that you ride a bike instead of eating it, but there's just no cure for stupidity (or stubbornness). Isn't the subject called something like "fool-proof" or so in english?
Likewise, people who have reached this state should know what they are doing - if nothing else, then from all the warnings on the sites they visited when beginning their DIY journey.
I'm beginning to think that I have made my point clear, and until I get some meaningful, non-paranoid, reasoning from SY, I won't drag Terry's thread further off-track.
Jennice
If SY is to freeky on safety, why has he never suggested a Residual current operated circuit breaker? They take care of just about every worry he has.
Furthermore, you canot ever avoid dangerous voltages when it's a mains powered thing (unless you keep your hands out of the EUT).
In some cases, an incorrect "precaution" grounding can expose the user of greater hazard than a floating thing. (i.e. the symmetric power supply, which - despite all grounding precutions - can present a danger, even on the secondary side.)
An insulating (isolating?) transformer, again to break ground-relative potential hazards, can be another way to lower the risk.
It should be obvious to everyone that mains powered things can be dangerous. This is also the reason why most "providers" like Rod Elliot have several warnings on their sites and material. One can only warn and call for reason. An example (from real life): A scooter (motorcycle) manufacturer has to specifically state on a warning, that this bike contains no parts suitable for eating. It should be obvious to most that you ride a bike instead of eating it, but there's just no cure for stupidity (or stubbornness). Isn't the subject called something like "fool-proof" or so in english?
Likewise, people who have reached this state should know what they are doing - if nothing else, then from all the warnings on the sites they visited when beginning their DIY journey.
I'm beginning to think that I have made my point clear, and until I get some meaningful, non-paranoid, reasoning from SY, I won't drag Terry's thread further off-track.
Jennice
Just as a clarification, my status as moderator is irrelevant unless a badge is showing. Same rules as everybody else.
You misunderstand the safety issue- I've been working as a professional and an amateur around circuits and measurements for a long time (though not these days), longer than most of the diyAudio.com participants have been alive. In that time, I've seen a lot of smart people have a careless moment. A careless moment in this kind of hookup can be lethal.
No use walking across the tightwire, no matter how great your sense of balance, when there's a perfectly good footpath.
You misunderstand the safety issue- I've been working as a professional and an amateur around circuits and measurements for a long time (though not these days), longer than most of the diyAudio.com participants have been alive. In that time, I've seen a lot of smart people have a careless moment. A careless moment in this kind of hookup can be lethal.
No use walking across the tightwire, no matter how great your sense of balance, when there's a perfectly good footpath.
Netlist dug up this comprehensive link (for which, my thanks):
http://www.tek.com/Measurement/cgi-...-float/eng/safety.html&FrameSet=oscilloscopes
http://www.tek.com/Measurement/cgi-...-float/eng/safety.html&FrameSet=oscilloscopes
I've been looking through this thread and its discussion of floating oscilloscope chassis. As a consequence I've looked at the manuals for two of my oscilloscopes.
The Tek 465 is a 1970s analogue oscilloscope, and like all of its kind, it has its input BNCs connected to chassis and thence to mains earth. The service manual very specifically states that it is designed for operation with a separate safety-earth conductor (ie not floating).
The Tek TDS3000 series digital oscilloscope has provision for battery operation and is in a plastic case with plastic controls, possibly implying that it might be safe to float it if operated from a battery. Nevertheless, it has a clear warning on the back, "Always connect the rear panel ground terminal to earth ground when operating the instrument from battery power."
Both oscilloscopes have their input BNCs bonded to the earth pin of the mains supply. As has been pointed out elsewhere in this thread, almost all test equipment such as generators etc has a connection to mains earth.
Attempting to make a high-side measurement of ripple current by measuring voltage drop across a series resistor is dangerous, and it doesn't matter if the probe has a plastic BNC (that's only so that it can support the additional pins that allow the probe and oscilloscope to talk to one another). I am aware that it used to be common in the TV repair industry to float oscilloscopes, but that was still dangerous, even though the people doing it were experienced.
It's important to remember that the vast majority of diyAudio members are not experienced electronics engineers and are unable to make a proper risk assessment. It behoves those of us that do know what we are doing not to encourage practices that could be misinterpreted by a neophyte.
When it comes to safety, you only have to be unlucky once...
The Tek 465 is a 1970s analogue oscilloscope, and like all of its kind, it has its input BNCs connected to chassis and thence to mains earth. The service manual very specifically states that it is designed for operation with a separate safety-earth conductor (ie not floating).
The Tek TDS3000 series digital oscilloscope has provision for battery operation and is in a plastic case with plastic controls, possibly implying that it might be safe to float it if operated from a battery. Nevertheless, it has a clear warning on the back, "Always connect the rear panel ground terminal to earth ground when operating the instrument from battery power."
Both oscilloscopes have their input BNCs bonded to the earth pin of the mains supply. As has been pointed out elsewhere in this thread, almost all test equipment such as generators etc has a connection to mains earth.
Attempting to make a high-side measurement of ripple current by measuring voltage drop across a series resistor is dangerous, and it doesn't matter if the probe has a plastic BNC (that's only so that it can support the additional pins that allow the probe and oscilloscope to talk to one another). I am aware that it used to be common in the TV repair industry to float oscilloscopes, but that was still dangerous, even though the people doing it were experienced.
It's important to remember that the vast majority of diyAudio members are not experienced electronics engineers and are unable to make a proper risk assessment. It behoves those of us that do know what we are doing not to encourage practices that could be misinterpreted by a neophyte.
When it comes to safety, you only have to be unlucky once...
High side??? 
I thought we were talking current measurements on the secondary. This is why I got long-winded about the differnces regarding class I and class II equipment.
SY,
If the foot-path takes you on an extremely long, or un-mapped detour, and you have a safety-net right underneath you, there's not much trouble involved.
You're promoting current clamps as being THE gadget. However, bandwidth and precision must be considered, and you may end up having to make modifications to your circuit which could involve other problems, as well as alter the result.
Again, why not use the isolation transformer, giving you a free-way of options, instead of either the footpath or the high-wire?
Jennice
Btw.: Some indication of the moved posts would have been appropriate. I found it by coincidence, and was about to get mad as it looked like censorship removed posts.
I thought we were talking current measurements on the secondary. This is why I got long-winded about the differnces regarding class I and class II equipment.
SY,
If the foot-path takes you on an extremely long, or un-mapped detour, and you have a safety-net right underneath you, there's not much trouble involved.
You're promoting current clamps as being THE gadget. However, bandwidth and precision must be considered, and you may end up having to make modifications to your circuit which could involve other problems, as well as alter the result.
Again, why not use the isolation transformer, giving you a free-way of options, instead of either the footpath or the high-wire?
Jennice
Btw.: Some indication of the moved posts would have been appropriate. I found it by coincidence, and was about to get mad as it looked like censorship removed posts.
This is a good overview of insulation categories that is relatively easy to understand. If you want more references, then I can keep pumping them out 'till the cows come home. But they all say the same thing. If a piece of certified test gear does not specifically say you can use it in a certain manner, then it is unsafe to do so.
It's that simple, folks...
It's that simple, folks...
Hi,
Here is TekTPS2000 specially designed for floating measurement.
Here is a little quiz: I designed a capacitor charging power supply charging 2 series connected banks of 4 10000uF/450V capacitors to +/-430V DC. Stored energy is high enough to defibrillate 20 persons in parallel. Charger complies with Class II requirements (reinforced insulation, 4000V AC test voltage). Capacitor bank provides pulsed power for operation of Class I rated (protectively earthed metal enclousere) medical device. Sometimes service personnel must operate the device with protective covers open and make some measurements and adjustments.
Now I would like to hear your expert opinion whether it is safer (for the service personnel) to float the capacitor bank or protectively earth it. I would also like to hear your reasoning why one decision is safer than another.
Best regards,
Jaka Racman
Here is TekTPS2000 specially designed for floating measurement.
Here is a little quiz: I designed a capacitor charging power supply charging 2 series connected banks of 4 10000uF/450V capacitors to +/-430V DC. Stored energy is high enough to defibrillate 20 persons in parallel. Charger complies with Class II requirements (reinforced insulation, 4000V AC test voltage). Capacitor bank provides pulsed power for operation of Class I rated (protectively earthed metal enclousere) medical device. Sometimes service personnel must operate the device with protective covers open and make some measurements and adjustments.
Now I would like to hear your expert opinion whether it is safer (for the service personnel) to float the capacitor bank or protectively earth it. I would also like to hear your reasoning why one decision is safer than another.
Best regards,
Jaka Racman
Jennice said:
Agree. A good sized isolation transformer is probably one of the most overlooked yet essential pieces of equipement to have at hand on the bench.
The equipment under test should always be isolated from protective earth (WAIT DON'T JUMP YET) and a separate and reliable connection to earth ground should be carefully probed first and established. This connection can be anywhere (well almost, high frequency high voltages nodes like a flyback secondary are not good idea because of stray capacitive coupling of the rest to earth). This connection is the ground reference for the scope and further measurements.
In your case, a power supply rail fits the bill, you can change the earthing connection to any rail in turn or other parts. Common sense dictates earthing of a low level signal node is not a good idea (neither necessary upon close inspection).
Make the earthing connection PERMANENT (no clips please) for the duration.
Rodolfo
As I understood the entire situation, the resistor was in the circuite to begin with... that's why I wanted to use it.
I know thew peak currents of the circuit would be different if it was shunted, but as long as it's in the circuit anyway, I want to use it.
Wasn't there someone who suggested to use the subtracting function of a 2ch scope, as an alternative?
I have not yet had time to read pinkmous' second link, but the national link is good overall reading for most DIY'ers.
One should keep in mind, however, that its referenced norms are out-dated.
Also, there's a thing on the example type plate (on page one) that bugs me.
They say, that the presence of the CE mark shows conformity with all applicable standards.
That should, for all equipment (other than equipment covered by the machinery and/or medical directives) be:
The presence of the CE mark shows, that the manufacturer claims conformity with the relevant standards. Having worked in a certification company for a number of years, I know that a lot of the cheap consumer stuff out there has a hard time complying with some of the directives, escpecially the EMC directive.
I know thew peak currents of the circuit would be different if it was shunted, but as long as it's in the circuit anyway, I want to use it.
Wasn't there someone who suggested to use the subtracting function of a 2ch scope, as an alternative?
I have not yet had time to read pinkmous' second link, but the national link is good overall reading for most DIY'ers.
One should keep in mind, however, that its referenced norms are out-dated.
Also, there's a thing on the example type plate (on page one) that bugs me.
They say, that the presence of the CE mark shows conformity with all applicable standards.
That should, for all equipment (other than equipment covered by the machinery and/or medical directives) be:
The presence of the CE mark shows, that the manufacturer claims conformity with the relevant standards. Having worked in a certification company for a number of years, I know that a lot of the cheap consumer stuff out there has a hard time complying with some of the directives, escpecially the EMC directive.
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