Re: [volt-nuts] Wavetek 1281 - Selfcal Module

[Todd Micallef]

No problem. I was just looking back at the documents wondering if I missed
anything. The transformer solution is interesting and I see that the 8508A
has a second low voltage transformer (T1). I have no idea if it performs
the same function using a different calibration.

On Sat, Oct 31, 2015 at 9:33 AM, Frank Stellmach  wrote:

> Todd,
>
> you already have sent me the appropriate SelfCAL circuitry, but I did not
> recognize (understand) it as such!
>
> I also received a hint from another volt-nuts, John, about the complete
> documents for the DATRON 1271 on the KO4BB site, which is very similar, and
> also contains a SelfCAL module, being a bit different than the one inside
> the 1281.
>
> The schematics for the 1271, anhow reveal how the transformer inside this
> module provides different voltage ratios. The transformer there is labelled
> +9.93V, +/-7.23V (that's the main references value), 1.83V, 1.00V and 0.19V.
>
> These ratios were generated with a precision switch mode / chopper
> circuit, and as the ratios on a transformer are very stable, you only have
> to measure them once during initial calibration.
>
> Obviously that is good for ppm ratio accuracy in the SelfCAL procedure.
>
> So thanks again
>
> Frank
>
>
>
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Re: [volt-nuts] Wavetek 1281 - Selfcal Module

[Todd Micallef]

Ok, I will look at them again. 

Sent from my iPad

> On Oct 30, 2015, at 07:26, Frank Stellmach  wrote:
> 
> Hello Todd,
> 
> many thanks for the reference schematics.
> 
> But that's not the SelfCAL module.
> 
> This should be capable of doing precise 10:1 ratio transfers, (I'm guessing), 
> so recalibrating all ranges and reducing the T.C. You'll find this 
> improvement (by a factor of nearly two) in the specifications, its key word 
> is "Enhanced" specification
> 
> Maybe, when you find some time again, please have a deeper look into the 
> documents.
> 
> Maybe, in the other service manuals, there might be a 'Theory of Operation' 
> chapter?
> 
> Frank
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Re: [volt-nuts] Wavetek 1281 - Selfcal Module

[Todd Micallef]

I recently picked up a 1281 that is throwing a couple of errors. While
researching the problem, I looked for the SelfCAL description and did not
see anything conclusive. I will pull out my schematics and see if there are
any references to a particular module. I was under the impression they were
using the second LTZ1000 reference module for this function but was never
certain.

I have the full repair manuals of the 1281 from Manuals Plus before they
stopped selling. I will look up anything I can find this evening.

Todd

On Thu, Oct 29, 2015 at 11:59 AM, Frank Stellmach <
frank.stellm...@freenet.de> wrote:

> Hello,
> I'm comparing different "AUTOCAL" techniques, like in the HP3458A, Fluke
> 5440A, 5720A, and have recently discussed  the 34465A/34470A "ACAL" feature
> with Keysight.
>
> The Datron 1281 had a SelfCal feature, which is briefly described as
> relying on a special SelfCal module inside this instrument. This should
> enable the instrument to make a complete (?) recalibration possible,
> between the annual calibration dates, or during room temperature changes,
> maybe comparable to the 3458A ACAL.
>
> The Fluke 8508A is obviously based upon the Datron 1281, but does not have
> this SelfCAL feature & module.
>
> Now, here's my question:
>
> Does any volt-nuts here, have an idea, what's hidden behind this 1281
> SelfCAL module, and how its capability is, also regarding its specification
> improvement?
> Are there any schematics or descriptions available?
>
> Thanks - Frank
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