isolation transformer
- Thread starter shaw0486
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Is this for safety in a health care facility, or is it for noise suppression, or impedence matching?
There are a lot of types of isolation transformers.
Steve
jcole
Senior Member
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- Lawrenceburg, Kentucky
I understand the noise suppresstion, but not the other two. Care to explain? I am curious too.
For operating rooms, it's sometimes safer to eliminate any connection between your power source and ground. With no connection to ground, it's impossible to be shocked by touching one line and ground. The current can't flow to ground because there wouldn't be any return path to the source. So to take a typical grounded supply and make it ungrounded, you use an isolation transformer. The transfomrer has no connections between the primary and the secondary, to the connection to ground is lost.
For impedence matching, I'm thinking about smaller transfomers that you would find in electronics.
Most isolation transfomrers include a grounded shield between the primary and secondary. This prevents capacitive coupling between the two windings.
Steve
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
Whereas strictly that is true that all non-auto transformers are isolating, when the word "isolation" is used it generally means that there is no electrical connection between the primary and the secondary. In a normal SDS installation sure the transformer isolates, but then the NEC requires that you bond the secondary right back to the primary, so the transformer is no longer doing any isolating at all!
Impedence matching is an interesting property. Many times in electronics it is necessary to connect stuff across an impedence difference. For example, professional audio microphone signals are balanced, approximately 600 ohm signals. To connect that to a high impedence unbalanced input stage you need an impedence changer, and a transformer can do that job. You can also do the job directly in electronics, but there are other properties of a transformer that can make it a desirable solution for this job, including noise supression, particularly of the common mode varienty, ie noise that is equally present on both legs of a balanced circuit.
If I remember correctly, impedence transformation occurs as the square of the turns ratio.
Impedence matching is an interesting property. Many times in electronics it is necessary to connect stuff across an impedence difference. For example, professional audio microphone signals are balanced, approximately 600 ohm signals. To connect that to a high impedence unbalanced input stage you need an impedence changer, and a transformer can do that job. You can also do the job directly in electronics, but there are other properties of a transformer that can make it a desirable solution for this job, including noise supression, particularly of the common mode varienty, ie noise that is equally present on both legs of a balanced circuit.
If I remember correctly, impedence transformation occurs as the square of the turns ratio.
LarryFine
Master Electrician Electric Contractor Richmond VA
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- Henrico County, VA
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- Electrical Contractor
Agreed. The traditional isolation transformer has a 1:1 ratio, and its sole purpose is isolation between the supply and the load. Auto-transformers do have a connection between primary and secondary.
They were popular in the olden days of tube TV and radio repair, as the chassis was connected to one side of the line, usually through a resistor or a capacitor, and made servicing a hazard; earphone jacks, too.
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