basics of autotransformer

On Tue, 15 Jan 2008 09:14:09 -0600 Ben Miller wrote: | Salmon Egg wrote: |> On 12/17/07 8:52 PM, in article GmI9j.800$pr3.209@pd7urf1no, "Don |> Kelly" wrote: |>

|>> You could have a 1:1 or untapped autotransformer but that would be |>> useless because it wouldn't do anything useful that a direct |>> connection without the autotransformer would accomplish - so -why |>> pay for something that does nothing useful, has losses, costs money |>> and complicates the circuit? |>

|> There are situations when you do not want to change voltage but do |> want isolation. Thus, and isolation transformer often is just a |> primary and a secondary winding relying upon the insulation to keep |> the secondary from connecting conductively to the primary. |>

|> One example where that may be wanted is when you are troubleshooting |> circuitry such as phase control circuitry with an oscilloscope. In |> the old days, before dual trace scopes were common, using a scope |> probe to measure waveforms between two points with a probe that had a |> ground lead could be a problem. With an isolation transformer, such a |> probe could be used between any two points in the circuit providing |> voltage ratings were not exceeded. |>

|> Bill | | I always thought you were supposed to cut off the ground pin on the scope | plug, and set the scope on a piece of cardboard for isolation! | (Oh yeah, and don't touch anything metal!)

I've always wondered how I was supposed to safely examine the power current waveform as sensed by the current transformer on service entrance wires coming into the building. NOT!

Sometimes some extreme isolation is really called for. In the above example my idea would be some kind of device serving as the current transformer that is transmitting the waveform by some wireless means, such as via an LED. Digital, or at least PWM, would be preferred to avoid any distortion issues.

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Call it laziness, I had immediate access to a 1:1 transformer so it was easier (and I was where it was a good idea to play it by the book).

Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer