Re: [volt-nuts] Ayrton Shunt does double duty.

[Bruce Griffiths]

The volt box is likely to be a voltage divider that was used to divide a 
voltage to be measured down to a value within the measurement range of a L & N 
potentiometer (not the 3 terminal component but the type that sets up the 
current in a series string of resistors to a known vale by comparing the 
voltage across a subset with the voltage of a standard cell. The unknown 
voltage can then be measured by comparing it against the voltage drop across a 
adjustable subset of the series resistor string).
They are mentioned in various NBS (NIST) publications of the era  as well as in 
various texts on dc electrical measurements. They were in common use up till 
around the 1980's.

Bruce
> On 05 May 2018 at 01:55 geoelectron...@rallstech.net wrote:
> 
> 
> Hello Dave. 
> 
> So far I have identified 3 different Leeds & Northrup "Boxes".
> Originally my intention was to re-purpose the box, panel connectors and
> switch for a project to make my own precision resistor banks. 
> 
> All use different switches and vastly different resistors to achieve
> their original purpose. 
> 
> The subject of the first one is the "Ayrton (wired) Shunt Box". It was
> used with a galvanometer as a sort of attenuator (current divider),
> uniquely wired in the Ayrton fashion to insure the galvanometer was
> always connected to a shunt resistor, even during switching. Think of
> the scheme as a stepped potentiometer, the meter was between the two
> extremes, while the source went to the wiper. Just backwards from a
> Voltage divider. 
> 
> Next is the "Shunt Box". It's resistors are copper straps, the lowest
> value is made from a copper sheet maybe 5 inches wide, bent into a
> corrugated shape to fit inside the box. Remarkable construction, should
> be quite stable as a milliOhm standard. 
> 
> The last one is called "Volt Box". Its resistors are wire wound on
> ceramic forms, obviously with great care. The switch is protected and
> possibly gold plated contacts. Multiple series connected resistors are
> used to provide the correct values plus spread the current (heat load)
> around, and they are spaced far apart and with air space around each
> one. So far no clue as to its original function but of course I have
> traced the schematic. 
> 
> Very little is freely available on the 'net about them nor a period
> catalog so far. 
> 
> George Dowell
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Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Bruce Griffiths]

Vibrating capacitor non contact field probe in feedback loop to create a 
voltage follower:

https://www.monroe-electronics.com/ESD/pdf/244a_m.pdf

Bruce

> 
> On 23 March 2018 at 15:12 Neville Michie  wrote:
> 
> Improvise by holding a metal disk over an electronic balance and 
> measuring the force of attraction.
> Calibrate it with a lower known voltage.
> 
> cheers,
> Neville Michie
> 
> > > 
> > On 23 Mar 2018, at 12:58, Dr. David Kirkby 
> >  wrote:
> > 
> > On 23 March 2018 at 01:49, kc9ieq via volt-nuts 
> >  wrote:
> > 
> > > > > 
> > > How about using (or building) an additional 2kV power supply 
> > > and a
> > > sensitive meter movement like a differential voltmeter, 
> > > adjusting
> > > for/measuring the null? Impedance at null will be 
> > > theoretically infinate,
> > > current will be theoretically zero, and you can 
> > > measure/monitor the voltage
> > > of your second supply directly with the probe/meter of your 
> > > choice.
> > > Regards,Chris
> > > 
> > > > > 
> > No, that will not work for me, as while the impedance at null is 
> > infinite,
> > it is not when not nulled, and that will mess up the measurements.
> > 
> > Absolute accuracy is not important. +/- 10% or even 20% would be 
> > okay. I
> > want to measure a couple of voltages and compare them. As long as 
> > the meter
> > reads the same with identical input voltages, that is fine.
> > 
> > Dave
> > 
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Re: [volt-nuts] How can I make a 2000 V DC meter with an input resistance of at least 100 T ohms?

[Bruce Griffiths]

Electrostatic voltmeter?

Either the classical version or the modern electronic variant perhaps?

Bruce

> 
> On 23 March 2018 at 13:33 "Dr. David Kirkby" 
>  wrote:
> 
> I want to measure a high voltage, but put minimal load on the circuit.
> Looking at the Keithley electrometers, the input resistance is at least 
> 200
> T ohms, but they tend to have a maximum of 200 V FSD.
> 
> A 2000 V source, and a 200 T ohm resistor gives a current of 10 pA, which
> itself is easy to measure. But one can't buy 200 T ohm resistors. I looked
> at RS in the UK, and the highest value resistor I could find is 1 T ohm,
> and they are £163 each (around $200).
> 
> Maybe fabricating ones own resistor is possible, but I suspect there's a
> better way. Keithely manage to keep a 200 T ohm resistance on the 200 mV
> range, and there's no way that can be measured with an ammeter, which 
> would
> require an ammeter with a full scale deflection of 1 fA, which is much
> smaller than the 2 pA FSD on its most sensitive range.
> 
> Any thoughts?
> 
> Dr David Kirkby Ph.D C.Eng MIET
> Kirkby Microwave Ltd
> Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
> Essex, CM3 6DT, United Kingdom.
> Registered in England and Wales as company number 08914892
> http://www.kirkbymicrowave.co.uk/
> Tel 01621-680100 / +44 1621-680100
> 
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Re: [volt-nuts] Bohnenberger electrometer

[Bruce Griffiths]

A method in use 40+ odd years ago for measuring atmospheric electric fields was 
to use a slotted rotating disk rather than the rotating cylinder.

A matching stationary or counter rotating disk IIRC was used either in front or 
behind the rotating slotted disk the the sensing disk was behind both.

Bruce.


> 
> On 17 March 2018 at 07:53 ed breya  wrote:
> 
> There is another kind of static electric field meter that was commonly
> used over the past few decades for monitoring charges/voltages in work
> areas dealing with sensitive semiconductors. It has a small motor
> spinning a hollow brass cylinder that has a radial hole or slot that
> alternately shields and exposes a center cylinder inside, which is the
> pickup electrode. This action causes a small AC signal on the electrode,
> that can be amplified up to represent the electric field strength from
> any nearby object. The signal is then rectified and trips a comparator
> and LED indicator if the level exceeds a certain amount.
> 
> I have a couple of these units, but have never experimented with them
> yet. They don't show any kind of readout or provide a measuring signal -
> just the LED warning of excessive (unknown trip point) static charge
> nearby. I figured someday I would modify one up and add a signal output
> port and a sync output from the motor, allowing a lock-in analyzer to
> read the result over a wide range, and maybe even be fairly accurate or
> calibrate-able.
> 
> Ed
> 
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Re: [volt-nuts] Vibrating reed electrometers

[Bruce Griffiths]

The Keithley model 640 was a vibrating capacitor electrometer.

It was available in the 1970's.

Bruce

> 
> On 04 March 2018 at 06:34 george  wrote:
> 
> Hi all
> 
> To the best of my memory Keithley never made vibrating reed 
> electrometers, the only one that I am aware of is the Varian Cary 401 which 
> did use Sapphire insulators. I was the European product line specialist for 
> Varian Cary in the late 1960/1970 era and was involved with the 401.
> 
> George G6HIG
> 
> 
> From: volt-nuts  on behalf of 
> volt-nuts-requ...@febo.com 
> Sent: 03 March 2018 17:00
> To: volt-nuts@febo.com
> Subject: volt-nuts Digest, Vol 103, Issue 3
> 
> Send volt-nuts mailing list submissions to
> volt-nuts@febo.com
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> Today's Topics:
> 
>1. Re: Precision high resistance measurements / calibration of
>   HP 4339B high-resistance meter. (ed breya)
>2. Re: Precision high resistance measurements / calibration of
>   HP 4339B high-resistance meter. (Mitch Van Ochten)
> 
> --
> 
> Message: 1
> Date: Fri, 2 Mar 2018 09:22:32 -0800
> From: ed breya 
> To: volt-nuts@febo.com
> Subject: Re: [volt-nuts] Precision high resistance measurements /
> calibration of HP 4339B high-resistance meter.
> Message-ID: <5f6e418c-649b-70e8-8502-facf1176f...@telight.com>
> Content-Type: text/plain; charset=utf-8; format=flowed
> 
> Oops - I think I didn't send this message properly yesterday - here goes
> again. Ed
> 
> Yes, David, unless you go to very extreme measures, you won't see real R
> values that have any practical meaning beyond E12 ohms or so. Most
> practical insulation Rs may be around E12-E14 tops, unless you go to
> sapphire. Up in that region, the R may be all within a material, or
> include surface components like a film of dirt or moisture, or a
> fingerprint.
> 
> E11 resistors can be made to fairly high precision, and maybe E12
> nowadays. In the old days, higher values were made by stacking E11s -
> like ten in series to get E12 with decent precision. The glass packaging
> also limits how high it can go, due to leakage within and on the
> surface. I once used a glass reed relay capsule as an ultra-high
> resistance in a circuit. There was no precision or stability at all, but
> it made a nice high resistor (probably E14-ish dry) even though there
> was no element in there, and the circuit didn't care, as long as it was
> very high, but not infinite.
> 
> The specs on this HP unit are likely just the most extreme capability
> taking maximum voltage over minimum current resolution, but any
> measurements would tend to be very noisy and unstable anyway. Also,
> testing at the extreme 1 kV makes the numbers seem more impressive, but
> the voltage coefficient of resistance will pretty much be unpredictable.
> 
> If this is a digital meter, then the other spec trick that tends to
> obscure the real performance limit is that the ultimate resolution and
> noise is that last digit - or even last two or three - that may may be
> pretty jumpy, unless very long averaging time is used.
> 
> There may be newer, fancier electrometers nowadays, but Keithley used to
> be the standard for these in the old days, before several digits of DVM
> resolution complicated the specs. They had a vibrating capacitor
> electrometer with all-sapphire input structure back in the 1970s/80s I
> think, that was the epitome of electrometers. I forget the model number,
> but vaguely recall that it could reach the aA region full scale - not
> that last digit of resolution thing. It's long obsolete, and I don't
> think they ever made anything actually better - only added 

Re: [volt-nuts] HP3458 ADC integrator

[Bruce Griffiths]

1) Reverse the supplies on U4 (in real circuit reversed supplies will fry the 
chip.)
2) Add 10k in series with reset switch
3) Swap connections to U4 inputs.
4) Use series shunt switch for reset switch as used in an actual 3458A.
Once done together with swapping in LT1220 for LT1225 rest works as expected 
and output slews due to gate current of J1 and input bias current of U1 

Bruce
> On 24 February 2018 at 10:23 Attila Kinali  wrote:
> 
> 
> On Fri, 23 Feb 2018 18:48:24 -
> "David C. Partridge"  wrote:
> 
> > Looking your schematic, I see that you are using LT1225 for both U2 (U111) 
> > and U3 (U112)
> > 
> > Why did you use those rather than LM6361 and AD848?  Was it just because 
> > LTSpice didn't have models for them?  It can make a difference ...
> 
> Yes. LTSpice doesn't have an LM6361 or AD848. Linear lists the LT1225
> as replacement for LM6361, so I thought this was safe. I deemed the AD848
> to be close enough.
> 
> But as Bruce mentioned, the LT1225 is not unity gain stable, while the
> LM6361 is. That might explain the oscillations.
> 
> > BTW LM6361 is 550V/mv not .55V (I assume that was a mistake in your post) 
> > ... 
> > Slew rates seem a bit different at +/- 15V supply as well.
> 
> The datasheet I have found (Natsemi Sept 1995) lists 550 V/V = 0.55 V/mV.
> Which I think is a bit low, but then, the opamp is old.
> 
>   Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>  -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [volt-nuts] HP3458 ADC integrator

[Bruce Griffiths]

Why do you think that the datasheet is wrong?

Its the same as the 1989 version.

A lot of the early wideband opamps didn't have high open loop gain.

Even the LT1220 only has about 7 - 15x more gain at rated load.

The LT1220 has a a pair of cascaded complementary symmetry emitter followers in 
its output stage compared to the single complementary symmetry emitter follower 
output stage of the LM6361.

Bruce

 

> 
> On 24 February 2018 at 11:05 "David C. Partridge" 
>  wrote:
> 
> > > 
> > The datasheet I have found (Natsemi Sept 1995) lists 550 V/V = 0.55 
> > V/mV.
> > Which I think is a bit low, but then, the opamp is old.
> > 
> > > 
> Check other datasheets, that's definitely wrong
> 
> David
> 
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Re: [volt-nuts] HP3458 ADC integrator

[Bruce Griffiths]

Attila

Some insight can be gleaned by using a single pole model for an opamp 
configured as an integrator and deriving the expression for the output signal.
Look at the non linearity in the output.
Look at the voltage at the inverting input.
The effective impedance at the inverting input due to feedback action can be 
modelled as a simple serries network. What are the network parameters?
What happens to the non linearity if the positive input is driven in such a way 
that the inverting input is held at ground?
How would one do this?
What does the resultant signal at the inverting input look like with real 
opamps?
Whats the maximum GBW of the corrector amp so that the phase margin of the 
combination isn't reduced too much? 

~30 years ago when I first analysed the limitations of opamp analog integrators 
I didn't have access to Spice and had to resort to Laplace transforms and 
analytical models of opamps. 

Bruce
> On 24 February 2018 at 10:23 Attila Kinali  wrote:
> 
> 
> On Fri, 23 Feb 2018 18:48:24 -
> "David C. Partridge"  wrote:
> 
> > Looking your schematic, I see that you are using LT1225 for both U2 (U111) 
> > and U3 (U112)
> > 
> > Why did you use those rather than LM6361 and AD848?  Was it just because 
> > LTSpice didn't have models for them?  It can make a difference ...
> 
> Yes. LTSpice doesn't have an LM6361 or AD848. Linear lists the LT1225
> as replacement for LM6361, so I thought this was safe. I deemed the AD848
> to be close enough.
> 
> But as Bruce mentioned, the LT1225 is not unity gain stable, while the
> LM6361 is. That might explain the oscillations.
> 
> > BTW LM6361 is 550V/mv not .55V (I assume that was a mistake in your post) 
> > ... 
> > Slew rates seem a bit different at +/- 15V supply as well.
> 
> The datasheet I have found (Natsemi Sept 1995) lists 550 V/V = 0.55 V/mV.
> Which I think is a bit low, but then, the opamp is old.
> 
>   Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>  -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [volt-nuts] HP3458 ADC integrator

[Bruce Griffiths]

Hint: start by looking at the summing junction voltage of a single opamp 
integrator with R = 50k, C = 330pF.

NB the LT1225 isnt unity gain stable so its use for any of U2, U3 and U4 is 
questionable.

They will all likely oscillate on their own. 

Bruce

> 
> On 24 February 2018 at 08:45 Bruce Griffiths <bruce.griffi...@xtra.co.nz> 
> wrote:
> 
> Moin attila
> 
> I'd start with simulating and understanding the integrator in the 34401A, 
> its a little simpler but still has a coupe of opamps in the integrator. Then 
> analysing the GBW requirements of the various opamps used in the HP3458A 
> shoul become somewhat clearer.
> 
> Bruce
> 
> > > 
> > On 24 February 2018 at 04:51 Attila Kinali <att...@kinali.ch> wrote:
> > 
> > Moin,
> > 
> > I am trying to understand how the HP 3458 integrator of its
> > dual-slope ADC works, as it's a bit more complicated than
> > a simple, single opamp integrator. As you can see from the
> > attached picture, it consists of 3 opamps (U1-U3) for the
> > integrator itself, and another for the slope amplification (U4).
> > Unfortunately, I do not get what U2 and U3 are doing, much less
> > why they are needed.
> > 
> > So I tried to simulate it in LTspice. But, the circuit oscillates.
> > In both, the reset state (when the integration-C shorting switch is 
> > closed)
> > and the integration state (though, less wildly so). I guess, this
> > is because I replaced the LM6361 and AD848 by the LT1225 but do not
> > understand why, or respectively, which of the differing parameters 
> > of
> > the LT1225 causes this oscillations.
> > 
> > Would someone be so kind and give me some hints?
> > 
> > Thanks in advance
> > 
> > Attila Kinali
> > 
> > --
> > It is upon moral qualities that a society is ultimately founded. All
> > the prosperity and technological sophistication in the world is of 
> > no
> > use without that foundation.
> > -- Miss Matheson, The Diamond Age, Neil Stephenson
> > 
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Re: [volt-nuts] HP3458 ADC integrator

[Bruce Griffiths]

Moin attila

I'd start with simulating and understanding the integrator in the 34401A, its a 
little simpler but still has a coupe of opamps in the integrator. Then 
analysing the GBW requirements of the various opamps used in the HP3458A shoul 
become somewhat clearer.


Bruce

> 
> On 24 February 2018 at 04:51 Attila Kinali  wrote:
> 
> Moin,
> 
> I am trying to understand how the HP 3458 integrator of its
> dual-slope ADC works, as it's a bit more complicated than
> a simple, single opamp integrator. As you can see from the
> attached picture, it consists of 3 opamps (U1-U3) for the
> integrator itself, and another for the slope amplification (U4).
> Unfortunately, I do not get what U2 and U3 are doing, much less
> why they are needed.
> 
> So I tried to simulate it in LTspice. But, the circuit oscillates.
> In both, the reset state (when the integration-C shorting switch is 
> closed)
> and the integration state (though, less wildly so). I guess, this
> is because I replaced the LM6361 and AD848 by the LT1225 but do not
> understand why, or respectively, which of the differing parameters of
> the LT1225 causes this oscillations.
> 
> Would someone be so kind and give me some hints?
> 
> Thanks in advance
> 
> Attila Kinali
> 
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
> 
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Re: [volt-nuts] Prema 6048 zero offset problems

[Bruce Griffiths]

Result of nonlinearity and dc offset combined?

Bruce

> 
> On 19 January 2018 at 00:57 "David C. Partridge" 
>  wrote:
> 
> Starting with a warmed up Prema 6048, if I power it off and then on, 
> select
> 20V DC range, 4 second integration and connect to the 10V output of a 
> Fluke
> 732A, I get a reading of:
> 
> +10.47
> 
> If I reverse the polarity of the cables and allow the reading to settle 
> down
> for a minute, I get a reading of:
> 
> -10.06
> 
> If I short the inputs of the meter, I get a reading of:
> 
> +0.000105
> 
> which is different from the +0.20 which I would have expected from the
> readings of the 732A output.
> 
> Proceeding on the assumption that the meter has stored a zero offset of
> -105uV
> 
> I then press the ZERO button to null out the offset and then reconnect the
> 732A in normal polarity I get an incorrect reading of:
> 
> +10.000153
> 
> This is not what I would expect to see - I would expect to see a reading 
> of
> +10.47 - 0.000105 = +09.42 This calculation
> 
> I then reverse the inputs and get a reading of:
> 
> -10.000113
> 
> which is close to the expected reading of -10.06 - 0.000105 = 
> -10.000111
> 
> I have mailed Prema about this problem, and will let you know what they 
> have
> to say.
> 
> Cheers
> David Partridge
> 
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Re: [volt-nuts] PCBs with ceramic substrates

[Bruce Griffiths]

When the glass fibre bunch periodicity approaches a significant fraction of a 
wavelength the periodic spatial modulation of the substrate dielectric constant 
under or surrounding transmission lines has interesting  effects on the 
properties of the transmission line. At even higher frequencies the surface 
texture of the copper also becomes an issue. Ditching glass fibre in favour of 
small ceramic particles eliminates the effect of the periodic spatial 
modulation of the substrate dielectric constant. Just as with dielectric 
absorption it should be possible to fit a Cole-Coles or similar model to the 
variation of dielectric properties (including loss) with frequency.

Bruce

> On 17 April 2017 at 15:54 cheater00 cheater00 <cheate...@gmail.com> wrote:
> 
> 
> Thanks, that second article had exactly what I had in mind. I would love 
> to see that permittivity vs freq graph in more detail around one of the flat 
> crossings of the saw graph with the smooth fitted curve, maybe +/- 10 MHz 
> around that crossing (not around the steep jump)
> 
> If ceramic is fragile and FR4 can be hook less then I assume FR4 is 
> better, testing anyways doesn't hurt.
> 
> The periodicity of the "saw" graph is telling. Could this have to do with 
> the size of layers created by the fibers, or the size of fibers themselves or 
> their spacing? Maybe a random fiber dimension (diameter, spacing) would be 
> better here than using a constant dimension of fibers.
> 
> 
> On Mon, 17 Apr 2017 05:35 Bruce Griffiths, <bruce.griffi...@xtra.co.nz 
> mailto:bruce.griffi...@xtra.co.nz > wrote:
> 
> > > 
> > There's little out there on the frequency dependence of dielectric 
> > constant at audio and sub audio frequencies.
> > 
> > A bit more for 10MHz and above like:
> > 
> > 
> > http://www.edn.com/design/analog/4398951/2/What-PCB-material-do-I-need-to-use-for-RF-
> > 
> > 
> > http://ac.els-cdn.com/S1474667015373043/1-s2.0-S1474667015373043-main.pdf?_tid=2e1d6d30-231a-11e7-84ab-0aab0f26=1492398280_a0295abea04d2b08db9f227ee52506fc
> >  
> > http://ac.els-cdn.com/S1474667015373043/1-s2.0-S1474667015373043-main.pdf?_tid=2e1d6d30-231a-11e7-84ab-0aab0f26=1492398280_a0295abea04d2b08db9f227ee52506fc
> > 
> > 
> >  There's also the article in The October 8 1978 issue of 
> > electronics on
> > 
> > Getting rid of hook: The hidden pc-board capacitance by authors 
> > from Tektronix and Norplex.
> > 
> > This article is in the files section of the Tekscopes yahoo group.
> > 
> > Otherwise there are various values given in the literature and on 
> > the web for the low frequency relative permittivity of FR4 which are all 
> > noticeably higher than the value at 10MHz.
> > 
> > Bruce 
> > 
> > > > > On 17 April 2017 at 14:31 cheater00 cheater00 
> > <cheate...@gmail.com mailto:cheate...@gmail.com > wrote:
> > > 
> > > 
> > > Thank you. Do you have a plot of the effect on impedance due 
> > > to hook out into high frequencies, measured on a real world material? It 
> > > would tell me a lot.
> > > 
> > > 
> > > On Mon, 17 Apr 2017 04:19 Bruce Griffiths, 
> > > <bruce.griffi...@xtra.co.nz mailto:bruce.griffi...@xtra.co.nz > wrote:
> > > 
> > > > > > > 
> > > > Hook is merely a manifestation of the variation of 
> > > > dielectric constant with frequency.
> > > > 
> > > > It affects the frequency response and transient of 
> > > > resistive attenuators by requiring more complex compensation than 
> > > > merely adjusting a trimmer cap to equalise the low frequency and high 
> > > > frequency attenuation. Since the dielectric "constant" (relative 
> > > > permittivity) of all dielectrics is frequency dependent all dielectrics 
> > > > will exhibit hook to some extent. Some PCB substrates like some 
> > > > versions of FR4 and G10 exhibit a significant variation in the 
> > > > dielectric constant from the dc value to a somewhat lower value for 
> > > > frequencies even in he audio range let alone frequencies of several 
> > > > MHz. Achieving a flat frequency response where the dielectric 
> > > > associated with circuit board capacitances exhibits significant hook is 
> > > > a complex task. Circuit board hook even affects the impedance of 
> > > > printed transmiss

Re: [volt-nuts] PCBs with ceramic substrates

[Bruce Griffiths]

There's little out there on the frequency dependence of dielectric constant at 
audio and sub audio frequencies.

A bit more for 10MHz and above like:

http://www.edn.com/design/analog/4398951/2/What-PCB-material-do-I-need-to-use-for-RF-

http://ac.els-cdn.com/S1474667015373043/1-s2.0-S1474667015373043-main.pdf?_tid=2e1d6d30-231a-11e7-84ab-0aab0f26=1492398280_a0295abea04d2b08db9f227ee52506fc
 
http://ac.els-cdn.com/S1474667015373043/1-s2.0-S1474667015373043-main.pdf?_tid=2e1d6d30-231a-11e7-84ab-0aab0f26=1492398280_a0295abea04d2b08db9f227ee52506fc


 There's also the article in The October 8 1978 issue of electronics on

Getting rid of hook: The hidden pc-board capacitance by authors from Tektronix 
and Norplex.

This article is in the files section of the Tekscopes yahoo group.

Otherwise there are various values given in the literature and on the web for 
the low frequency relative permittivity of FR4 which are all noticeably higher 
than the value at 10MHz.

Bruce 

> On 17 April 2017 at 14:31 cheater00 cheater00 <cheate...@gmail.com> wrote:
> 
> 
> Thank you. Do you have a plot of the effect on impedance due to hook out 
> into high frequencies, measured on a real world material? It would tell me a 
> lot.
> 
> 
>     On Mon, 17 Apr 2017 04:19 Bruce Griffiths, <bruce.griffi...@xtra.co.nz 
> mailto:bruce.griffi...@xtra.co.nz > wrote:
> 
> > > 
> > Hook is merely a manifestation of the variation of dielectric 
> > constant with frequency.
> > 
> > It affects the frequency response and transient of resistive 
> > attenuators by requiring more complex compensation than merely adjusting a 
> > trimmer cap to equalise the low frequency and high frequency attenuation. 
> > Since the dielectric "constant" (relative permittivity) of all dielectrics 
> > is frequency dependent all dielectrics will exhibit hook to some extent. 
> > Some PCB substrates like some versions of FR4 and G10 exhibit a significant 
> > variation in the dielectric constant from the dc value to a somewhat lower 
> > value for frequencies even in he audio range let alone frequencies of 
> > several MHz. Achieving a flat frequency response where the dielectric 
> > associated with circuit board capacitances exhibits significant hook is a 
> > complex task. Circuit board hook even affects the impedance of printed 
> > transmission lines (eg stripline, microstrip, CPW etc).
> > 
> > Bruce
> > 
> > > > > 
> > > On 17 April 2017 at 13:54 cheater00 cheater00 
> > > <cheate...@gmail.com mailto:cheate...@gmail.com > wrote:
> > > 
> > > Are conformal coatings the right way to handle this?
> > > 
> > > I understand there are kinds of FR4 and G10 that don't have 
> > > hook. What does
> > > one do about hook - how are those substrates improved? How 
> > > does hook
> > > manifest in circuits?
> > > 
> > > On Mon, 17 Apr 2017 03:48 David, <davidwh...@gmail.com 
> > > mailto:davidwh...@gmail.com > wrote:
> > > 
> > > > > > > 
> > > > FR4 has problems with consistency. Samples can have 
> > > > problems with
> > > > hook, dielectric absorption, leakage, and sensitivity 
> > > > to humidity.
> > > > 
> > > > On Sun, 16 Apr 2017 12:08:07 +0100, you wrote:
> > > > 
> > > > > > > > > 
> > > > > Hi Chuck
> > > > > 
> > > > > But the context is "PCBs with ceramic 
> > > > > substrates". Are any of *those*
> > > > > tough? They may well be, perhaps you know of 
> > > > > some? It does not help us
> > > > > with the subject much if there are ceramics with 
> > > > > these amazing
> > > > > properties if they are not available as PCBs.
> > > > > 
> > > > > There is also the question of exactly what 
> > > > > properties of FR4 are
> > > > > limiting for "metrology" use.
> > > > > 
> > > > > John
> > > > > 
> > > > > __

Re: [volt-nuts] DAS-46

[Bruce Griffiths]

A CLD is merely a JFET with the gate connected to the source.Sometimes a source 
resistor may be included with the gate connected to the opposite end of the 
resistor to the end connected to the source.
Bruce 

On Monday, 30 January 2017 12:12 PM, Jerry Hancock  wrote:
 

 One of the items I am having trouble modeling is a CLD, current limiting 
diode, MCL1302.  The CLDs are used between he base and collectors on the output 
stage 2n2219 / 2n2905.  I swapped them on the board with no impact on the 
problem.  I can’t find CLDs in LTSPICE.

The other diode I can’t read and it is used cathode to cathode in a weird 
arrangement.  The diode is roughly 1/2 the length (in this case height) of a 
1n4148.  It measures as a diode with .51V forward.  I have a hard time telling 
if it actually has a cathode band.  I haven’t pulled it out but I guess I’ll 
have to and put it under the microscope to see if there is a number on it.  I 
have a lot of very low forward voltage switching diodes and Schottky type so I 
probably have it on-hand if I can get a number off of it.

I spent some more time on the circuit today.

By the way, even though the Parent company, was General Resistance, now Prime 
Technology, said they would sell me a CSA, they said they won’t share the 
schematic.

Thanks again.
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Re: [volt-nuts] low emf solder

[Bruce Griffiths]

Laser welding should work for either similar or dissimilar materials.At one 
time microwire PCBs  used stainless steel  wires were welded to stainless lands.
Bruce  

On Saturday, 29 October 2016 1:39 PM, Dr. David Kirkby (Kirkby Microwave 
Ltd)  wrote:
 

 On 28 Oct 2016 15:25, "Juris L"  wrote:
>
> Found reference to optimal emf solder composition cadmium/tin alloy
> (70 %/30 %) in JJ array measurement article page 12.

I wonder how practical it is to weld test leads, so there's no solder or
thermal EMF.

I know that this will sound crazy, and probably is, but could one weld
components to a PCB?

I don't even have the excuse of been drunk or taking drugs,  but I will
risk ridicule for making the above comment!  Sometimes thinking out of the
box is useful.

Dave.
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Re: [volt-nuts] Calibration of 34401A

[Bruce Griffiths]

Calibration of a 34401A is done electronically, however one needs to know the 
calibration security code.If unknown one needs to open the meter to enable 
calibration and then reassemble it and complete the calibration. The factory 
default calibration security code is HP034401 only 034401 need be entered from 
the front panel.Details are given in the service manual. Everything can be done 
from the front panel or over the HPIB.
A ~90ppm error shouldn't be a calibration issue as the initial calibration has 
to cope with the manufacturing tolerance for the LM399 internal reference.
For the 10V range the calibration source needs to be accurately known and 
within the [9, 11]Volt range.It also needs to be reversed to allow linearity 
calibration. 
Bruce 

On Wednesday, 12 October 2016 9:54 PM, Dr. David Kirkby (Kirkby Microwave 
Ltd)  wrote:
 

 I have a 'friend" (actually a person who I have never met, but is a pain in
the ***).

He sold a Agilent 34401A multimeter which the customer said is out of
specification and can not be adjusted.

Quickly scanning the measurent results,  the  meter is not showing results
with any huge errors  (say 1%), but which (if any) range it is out of
specification I don't know. Unlike the Keysight calibration certificates I
have seen, the measurement results doesn't show the upper and lower limits
for the specification of the meter,  so one can not tell from a quick
glance if the meter is out of specification. One would need to study the
detailed specification.

*IF* I understand correctly, (and the data is in Spanish which I don't
speak),  with an input of 9,0 V, the meter reads 9,99899 which  the
data  indicates is an error of  -91 uV/V with an uncertainty of 7..7 uV/V.

The lab said the meter can not be adjusted.  I don't know if they mean

1) This lab has no ability to adjust the meter.

OR

2) It is too far off to adjust.

Does anybody know if a 34401A can be adjusted by a competent 3rd party lab,
or are the details of how to adjust the meter not available outside of
Keysight?

Dave
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Re: [volt-nuts] Practical power supply noise testing

[Bruce Griffiths]

Its certainly a good way to quickly check if anythings drastically wrong and 
one could even compare them with a known source such as an LM317 based 
regulator with no ADJ pin bypass. If one can hear the noise then its possible 
that a sound card could make some meaningful measurements of the headphone amp 
output.
John, do you have any specs for the supplies?It would be nice to know the 
likely best case output noise level.
To measure the ripple of most supplies I usually just connect my USB scope (dc 
coupled) to the supply output.This certainly works (with my 14 bit scope at 
least) with E3610A/E3611A series supplies. For lower ripple supplies I use AC 
coupling.
The 100Hz (in my case) ripple shows up nicely in the FFT. 

Bruce
 

  From: Poul-Henning Kamp 
 To: Discussion of precise voltage measurement ; Brooke 
Clarke  
 Sent: Saturday, 2 July 2016 11:28 AM
 Subject: Re: [volt-nuts] Practical power supply noise testing
   

In message <5776e31d.7090...@pacific.net>, Brooke Clarke writes:

>Instead of headphones something like the HP 4395A [...]

Well, there is a slight difference in price there, isn't there ? :-)

-- 
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
p...@freebsd.org        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.
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Re: [volt-nuts] Practical power supply noise testing

[Bruce Griffiths]

I've used a pair of minicircuits phase modulators, a low noise OXCO, and a 
Timepod to do this.The phase modulators work best with about 9V input.The noise 
of my E3610A's is clearly evident as is the noise of an LM317 based regulator 
with unbypassed ADJ terminal.To achieve lower system noise a pair of preamps 
(one per phase modulator) is useful, however the noise need not exceptionally 
low as cross correlation lowers the effective preamp noise.
Bruce


  From: John Ackermann N8UR 
 To: volt-nuts@febo.com 
 Sent: Saturday, 2 July 2016 12:47 AM
 Subject: [volt-nuts] Practical power supply noise testing
   
I have several supposedly low noise bench power supplies that I want to check 
out.  They seem to work well but are quite old, so of course one wonders about 
the caps, etc.

Can someone suggest a practical test regime to verify power supply DC noise 
performance?  Preferably one that doesn't require building up custom low noise 
amps?

Thanks!

John
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Re: [volt-nuts] ADA4522

[Bruce Griffiths]

Why?The ADA4522 is unity gain stable with about 60 degrees of phase margin.The 
equivalent output inductance at unity gain is about 0.5u
 50 ohms in series with the 1uF output capacitance ensures an overdamped 
response.

Bruce
On Saturday, 9 April 2016 11:20 PM, "acb...@gmx.de"  wrote:
 

 not sure the TI filter circuitry, although very nice, is stable with the 
ADA4522. 
have not checked, but R2/C2 loop stabilizer may not work with ad4522.
would require analysis/test, but positive result would sure make this a great 
reference buffer amp.
if you do, would be nice if you let the group know.



> Gesendet: Samstag, 09. April 2016 um 00:38 Uhr
> Von: "Randy Evans" 
> An: "Discussion of precise voltage measurement" 
> Betreff: Re: [volt-nuts] ADA4522
>
> I would use a filter such as TI's SBVA010 app note, "Improved Voltage
> reference Filter has Several Advanatages" or the article by Walt Jung,
> "Build an Ultra-Low Noise Voltage Reference" in Electronic Design.
> 
> On Fri, Apr 8, 2016 at 1:02 AM,  wrote:
> 
> > Low frequency noise is very good, but is is high noise at about 800kHz
> > (chopper) and above (possible artifacts). That should be filtered,
> > depending on your application.
> > What did you foresee to get rid of it, or would you accept it? Simple RC
> > filter as indicated in the manual increases the output resistance.
> >
> >
> >
> >
> > > Gesendet: Freitag, 08. April 2016 um 03:35 Uhr
> > > Von: "Randy Evans" 
> > > An: "Discussion of precise voltage measurement" 
> > > Betreff: Re: [volt-nuts] ADA4522
> > >
> > > Sure, all good applications.  I am thinking of using it as an output
> > filter
> > > for a 10V reference to filter all noise above 10Hz,
> > >
> > > On Thu, Apr 7, 2016 at 6:27 PM, Daniel Mendes 
> > wrote:
> > >
> > > > Ada4522-2 and 4522-4 are stocked at mouser. What about summing all
> > outputs
> > > > to reduce noise? Or use as buffered outputs with good reverse
> > isolation...
> > > >
> > > > Daniel
> > > > Em 07/04/2016 13:31, "Randy Evans" 
> > escreveu:
> > > >
> > > > > Has anyone looked at the ADA4522 precision op amp from Analog
> > Devices.
> > > > It
> > > > > looks very intriguing with it's extremely low offset voltage drift
> > of 22
> > > > > nV/°C maximum.  The offset voltage is as high as 5 uV but this could
> > be
> > > > > nulled out and it should be very stable over temperature after
> > that.  It
> > > > > could be a great choice for a voltage reference circuit.  Looks quite
> > > > > inexpensive also, although AD only sell in tubes of 96 right now.
> > > > > ___
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[volt-nuts] monitoring LTZ1000 chip temperature

[Bruce Griffiths]

In order to understand the dynamics of the LTZ1000 temperature 
regulation loop better in order to estimate the chip temperature 
response due to ambient temperature fluctuations, I am attempting to 
produce a model of the thermal impedance of the chip by fitting a Foster 
RC ladder (later transforming this to the equivalent Cauer filter) to 
the transient thermal impedance charateristics of the LTZ1000.
The datasheet curves for the transient thermal impedance for the LTZ1000 
are inconsistent (they indicate a junction to ambient thermal resistance 
of around 170C/W) with the tabulated thermal resistance (unless this is 
just the junction to case thermal resistance - the datasheet doesnt 
actually specify which thermal resistance junction to case or junction 
to ambient is specified.)
Has anyone obtained transient cooling curves for the LTZ1000 to compare 
with the datasheet curves?
Even a measurement of the junction to ambient temperature difference as 
a function of heater dissipation would be useful.


Whilst monitoring the chip temperature when the heater is driven with a 
fixed power as used when measuring the transient thermal impedance is 
easily done by measuring the Vbe of the temperature sensing transistor 
Q2, monitoring the temperature of the LTZ1000 chip is a little tricky 
once the temperature regulation loop is closed as the temperature 
sensing transistor Q2 can no longer be used to sense chip temperature 
fluctuations.


However the base emitter voltage of Q2 could perhaps be used for this.

Bruce
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Re: [volt-nuts] Resistors for LTZ1000A circuit

[Bruce Griffiths]

Frank Stellmach wrote:

Dave,
well the schematic is the same as in the LT specification.
My PCB is a prototype, and I would not like to publish it, because it 
contains several bugs.
One one those bugs led to the first change of the initial LT 
specification, i.e. I discovered the parasitic diode in parallel to  
the heater, by reversing the polarity.


I did not put any taobao.. link anyywhere, so I don't know what you 
mean, sorry.


Frank
The datasheet heater circuit for the negative reference is still 
inconsistent with the block digram given on the datasheet in that the 
parasitic diode in parallel with the heater is formward biased.


Bruce
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Re: [volt-nuts] Fluke 332D

[Bruce Griffiths]

Dick wrote:

I need a little circuit help here -- I'm looking at the schematic of the 
chopper amp, A5A4, and I'm trying to figure out if this amp is inverting or 
non-inverting for DC signals, that is from pin 6 input to pin 4 output. I'm 
looking at the simplified diagram on page 102 of the PDF manual, Fig 8-1, 3 of 
3. The detailed circuit for the chopper is on page 104.

Best,
Dick Moore
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Inverting.

Bruce

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