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11th Jan 2021, 4:23 pm | #1 |
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RS 'Hygrade' Universal Output Xfmr.: data?
I've had this transformer in my possession for decades: I think I may now have a use for it. It's designed to match a range of source and load impedances. To that end, the primary has 5 connections; the secondary has 4. (Presumably that four is for 3, 8 and 15 ohms). But the primary?
Can anyone here give me the instructions for use of this item, please? Thanks. Al. |
11th Jan 2021, 4:35 pm | #2 |
Octode
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
only as a word doc and with Ratio's hope that's ok
as all i have |
11th Jan 2021, 5:24 pm | #3 |
Octode
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
The primary is rated at 60mA DC.
Ron |
11th Jan 2021, 5:29 pm | #4 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
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12th Jan 2021, 1:03 am | #5 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
Thank you all! On account of the age of this item - which I do not believe to be a particularly common item - I honestly thought that my request would draw a blank. Just goes to show how wrong can one be on occasions!
Al. |
16th Jan 2021, 1:10 am | #6 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
I measured the transformer ratios using the supplied config. data. To do that, I used a 300 Hz, 1.5 kHz and 5 kHz sinewave and a Tek. 'scope. I applied 600 mV to the secondary and measured the output at the primary. All the configs. as per the data sheet were measured, except for the C.T. (centre-tap) configs. There were no differences in the calculated ratios for the three test frequencies.
Much to my complete puzzlement, the measured ratios were nowhere near to those stated in the data sheet. I can only think of one (or more) of the following reasons to explain that: 1. This transformer is a different 'Hygrade' transformer than the one for which the supplied data refers to. 2. This transformer is defective. 3. My measurement technique is in serious error. But there are some possible clues: 1. In the supplied data, as the sec. connection go from A - B to A - C to A - D, the corresponding ratios go down in that sequence: by my measurements, they go up. 2. The data sheet gives connections for use as a centre-tapped primary: 1 - 4 - 5, where, presumably, 4 is the C.T. However, by measurement, 1 - 4 is 700 ohms, 7H; 4 - 5 is 100 ohms, 3H. That doesn't seem to 'fit' with tag 4 as the C.T. The temptation is to conclude that this transformer is defective, but any other thoughts to explain this strange result gentlemen? Al. |
16th Jan 2021, 1:21 am | #7 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
I'm not sure I would 100% trust inductance measurements unless I knew a lot about the tester.
Voltage ratios with a scope ought to be more trustworthy if there's something wrong there may be clues in the waveform. Don't trust your sig gen, measure the applied excitation, then measure each pri winding then you don't risk tripping over p-p versus RMS measurement (we've all done it) And remember that you'll get the voltage ratios. Square the numbers to get the impednce ratios which is what I think RS specify. David
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16th Jan 2021, 2:02 pm | #8 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
Input voltages applied and consequent output voltages were measured with the Tek. 'scope. The inductance measurements were made using a Marconi Universal Bridge type 868B, whose calibrations were checked about one year ago. I'm not putting any great reliance on those inductance (and resistance) measurements, but they do seem to indicate an inconsistency, as explained.
Having said all that, I am now wondering if the magnitude of the applied voltage was simply far too small: 600 mV. I will repeat my measurements with a larger input voltage. 3v. rms to the secondary will correspond to about 1 watt in 8 ohms: that seems far more typical & representative of 'reality'. . I'm also aware of the importance distortion, lack of: input signal and consequent output. I'll return with results later. Al. |
16th Jan 2021, 3:05 pm | #9 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
With a proper bridge, the inductance values ought to be real. Some of the little LCR meters can get well and truly confused trying to measure larger inductances.
It may be the effect of core non-linearity and any residual magnetisation. Bigger voltage would be my next step. David
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16th Jan 2021, 8:06 pm | #10 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
Re: Above post by David.
Paragraph 1: Agreed; matches my experience. Paragraph 2: My thoughts also. Paragraph 3: That is my next step. Al. |
16th Jan 2021, 11:09 pm | #11 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
I repeated the measurements with 1v. p/p on selected secondary taps.
► And I do believe I've now twigged what is going on . . . . The spec. sheet states for a primary C.T., the primary connections are 1 - 4 - 5. That implies that the C.T is tag 4. However, by measurement, the C.T is not tag 4 but is tag 2. And that corresponds to the resistance measurements of tags 1 - 2 and tags 2 - 5: each are 400 ohms. It seems that the numbering sequence 1,2,3,4,5 should be 5,4,3,2,1 (The tag numbers are stamped on the Paxolin top plate of the transformer, so it's not my dodgy eyesight nor getting confused!) Moreover, that above suspicion agrees with the following . . . With 1 v p/p on secondary tags A and B, the corresponding voltages on any pair of primary tags are in direct proportion to the resistances between that pair. To me, that is what I would expect - and it makes sense. The supplied data states that as the sec. connections go from A - B to A - C to A - D, the corresponding ratios go down in that sequence: by my previous measurements, they went up But with these new sets of tests, the reverse is the case! Hence, I can only conclude that my original 600 mV excitation level was too small - as I subsequently suspected. (Presumably, 600 mV is insufficient to take the xfmr. core around a sufficient area of its B-H loop). I feel a lot more assured about this xformer now. So the next step is to calculate the primary Zp for a given load, by Zp = (TR)²*RL, where RL = sec'y. load and TR = selected turns ratio. All-in-all, quite a change form the 'usual' fault-finding! Al. |
16th Jan 2021, 11:25 pm | #12 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
Yeah, it's the kind of thing that when I run into one, it seems like the universe is failing.
Anyway it's starting to look sensible. David (Suspecting that flight and prosthetic limbs are related...)
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17th Jan 2021, 12:14 am | #13 |
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Re: RS 'Hygrade' Universal Output Xfmr.: data?
This extract from the Sherlock Holmes novel 'The Red-Headed League' springs to mind . . . .
"The more bizarre a thing is, the less mysterious it proves to be. It is the common-place, featureless crimes which are really puzzling, just as a common-place face is the most difficult to identify". Al. |