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| Transformer phase angle error |
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| duak:
I wonder if the steel used in audio transformers is significantly different as they are designed to minimize distortion. I'll bet power transformers try to minimize losses and cost but let the other chc's fall as they may. PA systems often distribute the speaker drive over 70 V rated signal pairs so transformers for that might be one source to try out. Cheers, |
| schmitt trigger:
|O --- Quote from: Jester on December 20, 2018, 01:35:17 am ---Wraper, I was not asking for advice on how to design a circuit, it was a simple question about phase delay across a transformer. We were designing optically isolated circuits running on the high side decades ago. I'm not at liberty to share the details of the specification that we're working to, I can tell you that it must have a transformer, even if there may be better approaches. BTW I did read the data sheet and have 10's of thousands of a design that is running resistor coupled inputs that have been in the field for years. Have a nice day, no need to respond as none of what you have posted as been the least bit useful. --- End quote --- My post did provide useful information. >:( |
| djacobow:
short: " Can someone here characterize parameters of this part that the manufacturers do not characterize or control, because those parameters are not remotely relevant to the part's intended usage, so that I can design the part into a high volume precision measurement device that utterly depends on that uncontrolled, characterized parameter? No? Geez, you must all be f*king idiots. " |
| Zero999:
--- Quote from: Jester on December 19, 2018, 11:04:32 pm ---Well I dug through my transformer box and found an E-Core style 240 to 24V, and did a few unloaded measurements (just visual zero cross on the scope). With 120V into the 240V transformer, I'm only seeing about 18us lag, so about 0.4 degrees, not so bad. --- End quote --- That's good, now what voltage do you get on the secondary? I bet it's not 12V, with 120V in. The turns ratio is not accurately controlled and is usually slightly lower, than the primary/secondary because the secondary voltage drops under load and the transformer will be specified to give the rated voltage, under full load. If you just want to do zero crossing then fine, but if you want to perform voltage measurement, then each transformer will need to be individually calibrated. Get a voltage instrument transformer. It will be more expensive but probably cheaper than having to calibrate an ordinary transformer in house. |
| soldar:
--- Quote from: Jester on December 19, 2018, 01:00:36 pm --- Can anyone shed any light on typical phase angle error of small (non metering accuracy) transformers for example something like this: --- End quote --- An ideal transformer has no losses and provides ideal V*I transformation between both windings. An ideal transformer does not exist in reality. That is why it is called "ideal". A real transformer has parasitic resistances and inductances. It is far from ideal. Have a look at the equivalent circuit of a real transformer. http://electricalacademia.com/transformer/equivalent-circuit-transformer-referred-primary-secondary-side/ You can see in parallel with the input an inductance and resistance that represent the magnetizing current. No matter what you do the input and output current can never be totally in sync. The only thing you can do is design a transformer so as to minimize the unwanted magnetizing current (which basically means raising the inductance). Also, the magnetising current is a small part of the input current when the transformer is under full load but the percentage increases as the load decreases. This also means that the phase difference changes with load. It is not constant. |
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