BIll Ezell | 26 Jul 00:04 2014
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Re: 7071 noise

Mickle writes:

>Solartron 7071/7081 manuals don't have official information about the
>Only one of the docs - Instruments Test Specification - have a 10 V noise limits:
>"10 V noise - The rms noise of 10 readings at 10 V is measured. It must be less
>than 3 uV". This is roughly equal to 12 uV p-p (with p=0.998, f=10).
>My old measurements (7.5-digits, short, 5-10 minutes):
>0.1 V = 0.2 uV
>10 V = 5 uV

Correct, not quite sure what I was thinking there. Re-reading what the OP said, looked like he was measuring
the p-p reading over 10 mins. The posted values I gave were 'transfer standard' worst-case stability
values at full scale, which of course isn't noise, but is a passable average over the specified transfer
time limit.
An averaged measurement over 10 mins should be pretty close to within those values, and of course you
wouldn't make a precision measurement without averaging multiple samples.

I actually have a 7081, but that shouldn't matter for the noise measurement (except possibly for a selected
zener). My measured 7.5 digit p-p over 5 mins was 3uv (+2, -1). I've noticed that the average reading
variation is usually in that range, but looking at a histogram of a few hundred readings, there are
certainly occasional significant glitches of multiple microvolts. It's really hard to determine the
source of those kinds of glitches, which is why when I'm trying to make the best measurements I can, I
capture the samples and process them myself, throwing our any outliers.

I also decided to check calibration, because I haven't recalibrated in over a year. I use dual Datron 4910's
that I compare to each other, sending one out for Fluke calibration if they disagree by more than 2 ppm. I
used to pay for hot-shipping, but Fluke said not to bother.

Anyway, my 7081 has only drifted by 5ppm. I'm impressed.

(Continue reading)

Pete Lancashire | 25 Jul 19:14 2014

Eppley standard cell catalog ?

Looking for spec's on model 705489

-pete
Dave M | 24 Jul 06:36 2014
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Re: Matched resistors

Do you have easy, low cost access to an old Fluke 801 or 803 differential 
voltmeter?  These meters have a Kelvin-Varley divider inside that is 
composed of strings of resistors that are highly matched in value and 
tempco.  If I remember correctly, the highest decade is filled with a string 
of 40K resistors, each succeeding smaller decade value is 1/5 of the next 
higher decade, but all very well matched. They should all be very well aged 
by now too. (Just like wine... they get better with age).
Perhaps you could mix & match values to come up with suitable resistors for 
your project.  If your project is a one-off deal, then perhaps that approach 
could prove viable.

Cheers,
Dave M

> From: Tony <vnuts@...>

> Randy,
>
> Have you considered using multiple identical resistors to reduce the
> variance? Depending on who you believe, you can reduce the variance of
> the overall resistance by SQRT(N) where N is the number of resistors
> in series/parallel. Its not that easy to create a good search query
> for
> this but here is one such explanation:
>
> http://paulorenato.com/joomla/index.php?option=com_content&view=article&id=109:combining-resistors-to-improve-tolerance&catid=4:projects&Itemid=4
>
> Ideally they should all come from the same batch - ie. manufactured by
> the same machine from the same batch of materials. Obviously there's
> no
(Continue reading)

BIll Ezell | 23 Jul 22:17 2014
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Re: Solartron 7071 noisy

That's a little high, a bit worse that what I remember mine being.
According to the specs, you should expect about 0.1/0.6/4 uV for those 
ranges.
So, your 10V seems a bit noisy.
Question, what was your warmup time? These really take about 24 hours to 
fully stabilize.
Do you have the service guide? There are several internal adjustments 
that affect the total noise, might just need tweaking.

But, don't try to recalibrate the actual reference voltage unless you 
have a very good standard, of which a single Weston cell is not one of.

I'll give mine a check.

On 7/23/2014 12:00 PM, volt-nuts-request@... wrote:
> Hi Everyone,
>
> I have a problem. I bought a Solartron 7071 on Ebay.
> That Voltmeter seems working properly but I think it's too noisy.
> It passes Self Test and Initialize and the reading is consistent against
> a Weston Cell to the µV.
> But, when left with a short circuit as input the noise (maximum during 5
> min) is:
> 0.2µV for 0.1V scale
> 0.4µV for 1V scale
> 8µV for 10V scale
>
> Is it acceptable?
> Thanks for your help.
>
(Continue reading)

Charles Steinmetz | 23 Jul 02:40 2014

Re: Matched resistors

Randy wrote:

>I agree that there are potentially some serious unknown issues with drift
>due to time and temperature due to changes in leakage current, charge
>injection, etc.  I would think some serious characterization would be
>needed before this approach could be used.

I have used LTC1043s in the voltage-multiplier configuration, and 
based on that experience I believe you will find there are too many 
surprises hiding there to reach your error budget.  First, there are 
losses in the conversion -- IME, even when driving nothing but the 
non-inverting input of an LTC1050 chopper-stabilized opamp used as a 
follower, the output voltage of an LTC1043 doubler is quite a bit 
(50uV or more) less than [Vin * 2].  Second, the output of the 1043 + 
buffer is about 100x noisier than the output of the same reference 
followed by a non-inverting gain-of-two LTC1050 (on the order of 
100uVp-p for the 1043 + buffer, about 1uVp-p for the non-inverting 
gain-of-two amplifier in a 10Hz bandwidth, IME).  Also, the 1043 
noise is not symmetrical, so different DC meters may give readings 
that differ by 50uV from one another.

If you try the LTC1043, I'll be interested to see what you find.

Best regards,

Charles

Jean-Louis Noel | 22 Jul 18:19 2014
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7071 noisy?

Hi Everyone,

I have a problem. I bought a Solartron 7071 on Ebay.
That Voltmeter seems working properly but I think it's too noisy.
It passes Self Test and Initialize and the reading is consistent against
a Weston Cell to the µV.
But, when left with a short circuit as input the noise (maximum during 5 
min) is:
0.2µV for 0.1V scale
0.4µV for 1V scale
8µV for 10V scale

Is it acceptable?
Thanks for your help.

Bye,
Jean-Louis 
Frank Stellmach | 17 Jul 06:40 2014
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Matched resistors

Randy,

resistor matched in T.C. are extremely expensive, as the manufacturer 
(or yourself) would have to select these from a batch of many samples.

reistors with very small T.C. (<1ppm/K) would do the job also, but they 
also need to be stable over time, in shelf life opereation mode, i.e. 
P<10mW.

That means, you need those hermetically sealed VHP202Z from Vishay, T.C. 
is typically < 1ppm/K and they are stable to < 2ppm over 5years. But 
they cost already 80€ each, depending on tolerance.

I made a longterm observation of these and found these parameters confirmed.

Frank
Randy Evans | 17 Jul 02:44 2014
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Matched resistors

I am building a 10V voltage reference based on the LTZ1000 and the design
is essentially done but I am looking for a pair of matched resistors that
track very closely over temperature.  The absolute value of the pair is not
important, anything between 50K and 200K ohms would be ideal, but the
matching ratio is very important.

 I looked at the 100K ohm LT5400 quad resistor array from Linear Technology
but it has a worst case long term accelerated shelf life spec of 10 ppm (at
150C) matching ratio and long term matching ratio drift of <4ppm (at 70C).
 I would like something much tighter if possible since that would mean I
likely don't need an oven for a couple of ppm worst case accuracy over time
and temperature.  I can make the LT5400 work but I would need to do
temperature characterization and circuit compensation.  Doable but
undesirable.

Does anyone have any ideas for a good ratio matched resistor pair,
hopefully not too expensive?

Thanks,

Randy Evans
Kgoodhew | 14 Jul 05:14 2014
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Fluke 5200A repair

Hi Gerd.
             Yes R6 changes the output of the op amp by about 15 mv..
During further investigation I found the input to Q1 was sitting at -400 mv
when it should be at 0 +/- 100uv.
While disconnecting things to try and isolate where the 400 mv was coming
from the resistors in series with the +15 on the p/s regulator board decided
to smoke!
The excess load was on the A7 power amplifier board, so something appears to
have died on this board whilst I was testing, wether I caused it or it was
just a coincidence I do not know.
Using the transistor tester I first tested all the socketed transistors and
found the n channel fet Q1 that I had previously replaced had failed,
however this was not causing the overload condition on the +15 rail, nothing
shows up with an ohmmeter test on this rail by the way.
I then tested all the soldered in transistors and found a number that give
incorrect readings, so I will have to dismantle the board again and remove
these transistors to properly test them.
Your suggestion to run extension cables is a good idea as continually
removing the board to solder wires on to the points I want to measure is
slowly damaging the socket the board plugs into, as well as making it
difficult to do measurements.
So when I have the board disassembled I will run some cables to allow me to
operate the board out of the chassis.
Ken.

Date: Sun, 13 Jul 2014 21:42:23 +1000
From: Gerd <admin@...>
To: Discussion of precise voltage measurement <volt-nuts@...>
Subject: [volt-nuts]  Fluke 5200A repair.
Message-ID: <53C2709F.50406@...>
(Continue reading)

new | 11 Jul 22:11 2014

Re: volt-nuts Digest, Vol 59, Issue 13 4214 help needed

Thank you, Mitch for the Rubicon data!!!!!
Willy

On 7/11/2014 7:32 AM, volt-nuts-request@... wrote:
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> Today's Topics:
>
>     1. Re: AC Voltage Measurement Standards (Todd Micallef)
>     2. Fluke 5200A repair. (Kgoodhew)
>     3. Need info on L&N 4214 temp vs resistance plot.. (new)
>     4. Re: Need info on L&N 4214 temp vs resistance plot..
>        (Mitch Van Ochten)
>
>
> ----------------------------------------------------------------------
>
(Continue reading)

Randy Evans | 11 Jul 15:57 2014
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Latching Low Thermal EMF Relays

Does anyone know a good part for a latching Low Thermal EMF Relay for small
signal applications?  I found many Low Thermal EMF Relays but not latching
types.

Thanks,

Randy Evans

Gmane