Iosif George | 2 Aug 19:14 2015
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Solartron 7060 ROM image

Hi,

Any chance anyone has the ROM image from a Solartron 7060 multimeter?
I am trying to resurect one such meter and, unfortunately, the EPROM chip
has died.

Thank you!

Regards,
--

-- 
George
Chuck Harris | 29 Jul 05:35 2015
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Fluke 5200A instability...

Before I spend a lot more time on it, does anyone have any experience
with the Fluke 5200A's feedback loop oscillating when in the 100Hz band
position?

Mine started to oscillate at about a 1/2Hz rate a while back. It is two
to three orders of magnitude better when in the 1KHz and higher band
positions.

I can tell it is oscillating because if I watch the 3 least significant
digits on my 3456A voltmeter, in the AC position, they keep repeating
over and over and over... sort of fits a 1-2-3-1-2-3... count.

I have replaced the bad capacitors in the power supply, and on
a few of the boards.  I have checked the supplies for voltage and
ripple, and AFAIK they are ok.

I tested the 2uf mylar integrator cap that is employed while in the
100Hz band, and replaced more than a few carbon composition resistors
that were between 20 and 50% out of tolerance with no apparent affect.

The carbon composition resistors I replaced were used to digitally
adjust the gain of the integrator, so seemed likely to have an effect
on the stability criterion of the feedback loop..

The DC Reference voltage seems to be very stable, and can be selected
up and down with the voltage selection switches.

I have tested all of the tantalums for shorts, and found none.

I am running out of ideas.
(Continue reading)

Richard Moore | 28 Jul 22:26 2015
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Re: 3458A Zero reading

Randy — not sure why you feel the need for shielded wire for DC measurements, especially if you turn the LP
filter on, unless you live under a transmitter. I use twisted pair 22 ga. solid copper bell wire for voltage
measurments with no difficulties, and the thermals reduce very quickly. Silver plated copper would be
even better I suppose. Heavy gauge wire is only needed for current measurements, which I seldom do.

Dick Moore
Richard Moore | 27 Jul 21:57 2015
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Re: 3458A Zero reading


Randy — My 3458A manual specs 12 or 14 gauge solid copper wire for the short, bunt in to a U shape. I use 14
gauge. Poul-Henning’s comments about thermals are well-taken — even a simple folded up carboard
shield helps. But I think you’re near the limit.
Randy Evans | 27 Jul 04:15 2015
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HP-3458A Zero Reading

A bit of a false lead.  I took the readings after an hour of warmup.
However, after about two hours, the zero reading went to less thatn 0.2 uV,
which seems just fine to me.  I guess i just needed to get a really good
warmup time.

However, the 752 readings are varying over several uV when doing the CAL
procedure.  I am currently using unshielded leads so I suspect I am getting
a lot of noise.  Time to invest in some really good cables I guess.  I was
hoping to build my own cables as Bill Gold had suggested in a previous
thread.

Randy AE6YG
Randy Evans | 27 Jul 03:19 2015
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HP-3458A Zero Reading

I shorted the input terminals of my HP-3458A with a short lead of copper
wire, Bell telephone wire as recommended in the manual.  The reading I get
is around 000.00070 mV, or 0.7 uV with NLPC set to 100.  I was trying to
evaluate it's use as a null meter for my Fluke 752A divider.  This seems a
little higher than I would expect but no amount of running AUTOCAL or ZERO
changes this amount.  Is this considered acceptable?

Randy AE6YG
Randy Evans | 21 Jul 18:33 2015
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Test Leads

I recently acquired a Fluke 752A to go with my Fluke 732A and HP-3458A.
Now I need to address the need for low thermal test leads.  Does anyone
have any suggestions for test leads that have low thermal contributions to
measurements?  I have looked at Pomona 1756 Low Thermal EMF Cables as a
starting point but haven't found any other candidates.

I have heard that old TV twin lead works well since most are stranded
copper wire.  I have tried it between my 732A and 3458A and it seems to
work fine but I would like to use more professional looking test leads,
particularly with correct copper spade lugs (Pomona 2305 Low thermal EMF
spade lug, Gold-plated?).  Any other suggestions?

Thanks,

Randy Evans AE6YG
Charles Steinmetz | 7 Jul 04:58 2015

Re: Oven thermal insulation

Randy wrote:

>I am working on a voltage reference deisgn that will go into an oven for
>the highest stability.  I am looking for a good insulation material that
>can stand high temperatures safely (up to 80C).  Looking at some HP
>frequency standard ovens I see a hard, light-weight insulation material of
>some type that looks like it would work really well, but I have no idea
>what it is.  Does anyone have any suggestions?

I don't know what HP used, but polysulfone is the usual go-to plastic 
for insulation in that temperature range.  It is available in sheets 
and blocks and is machineable.

Do take care not to over-insulate -- the control loop depends on heat 
flow across the insulator to provide the "pull-down" to 
counterbalance the "pull-up" of the heater.  Too much insulation 
(thermal resistance) and the controller can raise the temperature 
quickly, but it takes forever to lower it when the controller 
overshoots (and controllers always overshoot some if they are set up 
for a normally-damped response).  This results in long settling 
times, instability, or even thermal runaway.  You want the pull-up 
and the pull-down to be roughly symmetrical (rise in internal oven 
temperature per unit time with heater fully on approximately equal to 
decline in internal oven temperature per unit time with heater off).

Generally, moderate thermal resistance combined with thermal 
capacitance (thermal mass) produce optimum system dynamics.

Best regards,

(Continue reading)

Randy Evans | 7 Jul 02:43 2015
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Oven thermal insulation

I am working on a voltage reference deisgn that will go into an oven for
the highest stability.  I am looking for a good insulation material that
can stand high temperatures safely (up to 80C).  Looking at some HP
frequency standard ovens I see a hard, light-weight insulation material of
some type that looks like it would work really well, but I have no idea
what it is.  Does anyone have any suggestions?

Thanks,

Randy Evans AE6YG

HP 741B AC-DC Differential Voltmeter/DC Standard

All-

Recently picked up an HP 741B, a cousin of the 740B. Wondered if anyone had ever heard of/used/owned this
particular model? Strikes me as somewhat of an odd beast in that it shares the same reference oven,
production period and ostensibly similar niche as the 740, with the notable addition of AC measurements,
yet it has slightly lesser performance (Stability is 3ppm/hr setting, 1ppm/hr range vs 1ppm/hr setting,
0.5ppm/hr range). Curious as to who the target market was? Seems like the 740B would be the choice for DC and
another mfr for AC, particularly since it doesn't offer a built in standard.

Beautiful cosmetic condition inside and out. No signs of someone messing around with the internals in a
past life. Reference oven is good and provides output on the 1V range, but unfortunately the 10, 100, 1kV
outputs are nil. Visual inspection didn't offer any overt failures, but given the issue is on all ranges
except that which is coming straight out of the ref, the issue likely resides between the diff amp/power
switch assy and output. For those in the know, everything probed as expected except the collectors of A7Q1
and A7Q2, which were flat.

Anyone have any pearls to share that may save me some time?

-Nick

Sam Reaves | 27 Jun 04:23 2015
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Re: volt-nuts Digest, Vol 70, Issue 16

Randy,

When I try to download the 500K PDF it shows up as 162K and will not open.

Sam

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(Continue reading)


Gmane