What differentiates a "bridging transformer" from an ordinary "isolation transformer"

Does anyone know what differentiates a "bridging transformer" from an ordinary "isolation transformer"?

The application is a calibration procedure for a synchro-resolver simulator. The setup drawing shows a shielded transformer -- labeled as a "bridging transformer" -- connecting two devices. The schematic of the thing is the same as what is on the case of something we purchased as an "isolation transformer". Depending on the particulars of the test step, the applied voltage would be from 0 to 90 V AC, 400 to 2000 Hz.

Since "electronics 101" was long, long ago and I don't have the proper reference book handy ... does anyone remember?

Thanks,

Bridging transformer is not a familiar term. Could it be acting as an impedance matching transformer, which, according to the maximum power transfer theorem, will allow more efficient power transfer between an input and output when input and output Z is matched (despite hysteric losses)?

I hope you'll forgive me for using second-hand information. According to http://www.dilettantesdictionary.com, bridging is:

"...The opposite of impedance-matching. When the input of an audio device is connected to the output of another device, it is a bridging connection if the second device does not appreciably load the first device and essentially no power is transferred. The second device is sensitive to the output voltage of the first device, and this is maximized when the loading is minimized. Most audio connections are bridging, and the load impedance is at least ten times greater than the source impedance. A bridging connection is made by connecting everything in parallel (all the plus inputs connect to the plus output, all the minus inputs connect to the minus output.) This not only allows for a number of loads to be connected to the same source before overloading it, but this also gets the maximum voltage swing possible from the source. "

Therefore, a bridging transformer (commonly used in audio applications) is a transformer for connecting a source to a load whereby you minimize loading effect.

An isolation transformer, I believe I recall, is more neutral, in that it simply provides isolation between two things. Using an isolation transformer (a variant being a Variac) to separate, for example, an instrument being calibrated from possible ground looping that could be created when plugged into a normal outlet. So I belive, electrically, they have different functions.

As Audio technician is one of my avocations (church sound man for 25 years), I use isolation transformers to eliminate ground loops between major system components.

Not sure how well this answers, but that's my two cents.

Jerry, a Variac is an autotransformer and does not isolate, since input and output share a common leg. Look here for a comparison.

My mistake regarding the Variac. I did know that (brain glitch). Anyway, my focus was on the bridging transformer.

Thank you, sir!

Jerry,

Thank you for that definition - it is very useful.

In this application, one side is connected to a synchro-resolver simulator and a ratio transformer (unbalanced and low impedance), and the other side goes to the input of a phase angle voltmeter (balanced higher impedance). So there is an impedance difference as well as connection issues. I later found out that the supplier of our device also states that it is an "equivalent" for the one originally specified. The proof test will be when we hook it up later in the week to see if it works!

ALSO - thank you for adding a previously unknown reference to my bookmark list!

Thanks again,

Graeme

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