Galvanic disconnection with transformer
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From: Kari Laine on 26 Mar 2010 14:55 Hi, first. Thank you for all the help I have gotten from here so far. Now I am trying to figure out how to connect the electricity to my scopes and the Power supply I am building. I don't know the right term for a transformer which disconnects galvanic connection between the electricity network and device. I will just use term transformer for that. I have - bench top HP oscilloscope - Velleman PCSGU250 PC-scope - Another Velleman on other machine - Daqarta sound-card oscilloscope And then I have the unsuspecting target - my PSU I want to scope the PSU's primary and secondary windings and later follow the voltage through it. On which devices to put the transformer? Then there is that ground lead in the probe. If there is transformers in the machine connected with the scope and the device under test, would be destructive to connect it at all? Because there is no common ground between the devices? I really need to get 1000 page book about oscilloscopes - ISBN anyone? I am learning this alone, so there is no one to ask except here.... Those transformers are pretty expensive, so my first thought to put them everywhere is not good one. I would be very thankful if someone(s) could tell little bit about the basics about this, with instructions what to do. And naturally what not to do. Best Regards Kari -- PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI - KEYPADS - ACCESSORIES http://www.byvac.com (I am just a satisfied customer)
From: pimpom on 26 Mar 2010 17:13 Kari Laine wrote: > Hi, > > first. Thank you for all the help I have gotten from here so > far. > > Now I am trying to figure out how to connect the electricity to > my > scopes and the Power supply I am building. > > I don't know the right term for a transformer which disconnects > galvanic connection between the electricity network and device. > I > will just use term transformer for that. It's called an "isolation transformer" or "isolating transformer". It isolates anything connected to the secondary from the public electricity supply lines. This makes it less dangerous to work with, but you still have to take care while doing anything at mains voltages. > > I have > - bench top HP oscilloscope > - Velleman PCSGU250 PC-scope > - Another Velleman on other machine > - Daqarta sound-card oscilloscope > > And then I have the unsuspecting target - my PSU > I want to scope the PSU's primary and secondary windings and > later > follow the voltage through it. > > On which devices to put the transformer? > > Then there is that ground lead in the probe. If there is > transformers > in the machine connected with the scope and the device under > test, > would be destructive to connect it at all? Because there is no > common > ground between the devices? I really need to get 1000 page book > about > oscilloscopes - ISBN anyone? I am learning this alone, so there > is no > one to ask except here.... > > Those transformers are pretty expensive, so my first thought to > put > them everywhere is not good one. I would be very thankful if > someone(s) could tell little bit about the basics about this, > with > instructions what to do. And naturally what not to do. The basic idea is this: You connect the primary (input side) of the isolation transformer to the mains outlet, and the primary of the PSU transformer to the secondary (output) of the isolation transformer. You can now measure voltages at various points on your PSU. But there are some complicating factors, especially since you want to measure the input to your PSU transformer, and that is still at mains voltage (and dangerous if you don't know what you're doing) even though it is isolated from the public mains. It's a bit complex and it's already close to 3:00 AM here now. So I'll have to sign off now and continue tomorrow unless someone else has given provided the answers by then.
From: Jasen Betts on 26 Mar 2010 17:51 On 2010-03-26, Kari Laine <klaine8(a)gmail.com> wrote: > Hi, > > first. Thank you for all the help I have gotten from here so far. > > Now I am trying to figure out how to connect the electricity to my > scopes and the Power supply I am building. > > I don't know the right term for a transformer which disconnects galvanic > connection between the electricity network and device. I will just use > term transformer for that. Isolating transformer > I have > - bench top HP oscilloscope > - Velleman PCSGU250 PC-scope > - Another Velleman on other machine > - Daqarta sound-card oscilloscope > > And then I have the unsuspecting target - my PSU > I want to scope the PSU's primary and secondary windings and later > follow the voltage through it. > > On which devices to put the transformer? On the PSU. > Those transformers are pretty expensive, Can be cheap second-hand, but pay a few bucks to get them tested if you do get a used one. --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: The Phantom on 26 Mar 2010 18:25 On Fri, 26 Mar 2010 20:55:37 +0200, Kari Laine <klaine8(a)gmail.com> wrote: >Hi, > >first. Thank you for all the help I have gotten from here so far. > >Now I am trying to figure out how to connect the electricity to my >scopes and the Power supply I am building. > >I don't know the right term for a transformer which disconnects galvanic >connection between the electricity network and device. I will just use >term transformer for that. > >I have >- bench top HP oscilloscope >- Velleman PCSGU250 PC-scope >- Another Velleman on other machine >- Daqarta sound-card oscilloscope > >And then I have the unsuspecting target - my PSU >I want to scope the PSU's primary and secondary windings and later >follow the voltage through it. > >On which devices to put the transformer? > >Then there is that ground lead in the probe. If there is transformers in >the machine connected with the scope and the device under test, would be >destructive to connect it at all? Because there is no common ground >between the devices? I really need to get 1000 page book about >oscilloscopes - ISBN anyone? I am learning this alone, so there is no >one to ask except here.... > >Those transformers are pretty expensive, so my first thought to put them >everywhere is not good one. I would be very thankful if someone(s) could >tell little bit about the basics about this, with instructions what to >do. And naturally what not to do. You could get one of these isolation transformers: http://www.mouser.com/catalog/catalogUSD/641/1971.pdf I have used this particular one: http://www.mouser.com/ProductDetail/Triad-Magnetics/VPS230-350/?qs=Fg5d7evCuampJb4iXfKS4A%3d%3d I can handle loads up to 80 VA. Depending on how much power your PSU is going to be drawing while you work on it, you could select a smaller or larger one to meet your needs. > >Best Regards >Kari
From: Kari Laine on 27 Mar 2010 07:40
Thank You for your time and effort. I am now convinced that one cannot measure mains with an oscscope connected to same mains. And it is recommended to use battery powered oscilloscope - why is that? I actually do not need to measure mains. I am sure the electrical company is good enough. I only have to measure ripple after the bridge before regulator and ripple after regulator. I am just curious what would happen if I do following. I have a PC-scope connected to machine, which is grounded through the mains cable. I connect probe (in x10) to mains? Will I generate smoke? Best Regards Kari -- PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI - KEYPADS - ACCESSORIES http://www.byvac.com (I am just a satisfied customer) |