Connecting 50 Ohm signal generator output to low impedance primary on transformer

Thread Starter

Ben1974

Joined Jan 7, 2015
5
Dear All,

To test the rotary signal transformer in our equipment I would like to use our Rigol DG4062 signal generator to feed the primary so I can use the scope to check the output at the secondary.

The primary resistance is about 1 Ohm so I can't connect directly due the impedance mismatch.

What would be the best way to connect the signal generator to this low impedance primary? I have had a look for an suitable impedance transformer but can't find anything.

Kind Regards

Ben
 

LesJones

Joined Jan 8, 2017
2,317
What do you mean by a "Rotary transformer" (The term was used over 60 years ago motor/generators to provide HT in WW2 surplus radio equipment but I don't think you are using the term in that way.) The DC resistance of a winding is not the same as it's reactance at some AC frequency. Are you testing the transformer at it's designed operating frequency ?

Les.
 

Thread Starter

Ben1974

Joined Jan 7, 2015
5
What do you mean by a "Rotary transformer" (The term was used over 60 years ago motor/generators to provide HT in WW2 surplus radio equipment but I don't think you are using the term in that way.) The DC resistance of a winding is not the same as it's reactance at some AC frequency. Are you testing the transformer at it's designed operating frequency ?

Les.

The transformer transmits the signals from a windings on stator to the windings on a rotating drum to transmit signals to and from test probes on the rotating drum. (It is a rotary eddy current tester).

Operating frequency is 50KhZ to 100Khz. I'm not sure what the reactance of the primary is but there are only 5 turns on large diameter ferrite core so would imagine pretty low.

Thanks
 

LesJones

Joined Jan 8, 2017
2,317
I would connect it to signal source via a 47 ohm resistor as Alec suggested in post #2 and mesure the voltage across the primary and across the signal generator output. From that you can calculate the apparent reactance of the transformer primary. From that result you may be able to use a lower value series resistor. Another thing you could try is using an audio power amplifier.(With it's input fed from the signal source.) It would probably give a reasonable percentage of it's rated output at 50 Khz.

Les.
 

Thread Starter

Ben1974

Joined Jan 7, 2015
5
I would connect it to signal source via a 47 ohm resistor as Alec suggested in post #2 and mesure the voltage across the primary and across the signal generator output. From that you can calculate the apparent reactance of the transformer primary. From that result you may be able to use a lower value series resistor. Another thing you could try is using an audio power amplifier.(With it's input fed from the signal source.) It would probably give a reasonable percentage of it's rated output at 50 Khz.

Les.
OK I'll give that a go. Thanks for the advice.
 
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