Hello George,
As the bible is full of contradictions, what is so valuable
about Grover?
73 de Brian, VK2GCE
?
?
The bible for inductance calculations is:
?
Inductance Calculations by FREDERICK-W-GROVER
?
Cheers,
George G
VK2KGG
?
?
?
I'm curious
where you found that calculator. I would've guessed something a bit over 10nH
for the plate, based on scaling the value for the wire. Not a huge difference,
but I'm curious to see what formula that calculator is using for the square
plate.
-- Cheers,
Tom
-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070
toggle quoted message
Show quoted text
On 9/15/2022 15:43, Mikek wrote:
>On another note: How
does inductance change from say, a 1" long 0.30" diameter wire vs a
1" x 1"? square 0.30" thick?<
Found a calculator, 1" wire 21.1nH, 1" square plate 7.1nH.
?
|
Indeed it is. I have various rules of thumb that were derived from
Grover, and in this case my thumb gave me a number that was 50%
higher than given by the online calculator, so that piqued my
curiosity.
-- Cheers
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 9/15/2022 17:51, Labguy wrote:
toggle quoted message
Show quoted text
The
bible for inductance calculations is:
?
Inductance
Calculations by FREDERICK-W-GROVER
?
Cheers,
George
G
VK2KGG
?
?
?
I'm curious where you found that
calculator. I would've guessed something a bit over 10nH for
the plate, based on scaling the value for the wire. Not a huge
difference, but I'm curious to see what formula that
calculator is using for the square plate.
-- Cheers,
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 9/15/2022 15:43, Mikek wrote:
>On another note: How does inductance change
from say, a 1" long 0.30" diameter wire vs a 1" x 1"?
square 0.30" thick?<
Found a calculator, 1" wire 21.1nH, 1" square plate 7.1nH.
?
|
The bible for inductance calculations is: ? Inductance Calculations by FREDERICK-W-GROVER ? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Tom Lee
Sent: Friday, 16 September 2022 9:03 AM
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] Making a Q-meter /? I'm curious where you found that calculator. I would've guessed something a bit over 10nH for the plate, based on scaling the value for the wire. Not a huge difference, but I'm curious to see what formula that calculator is using for the square plate.
-- Cheers,
Tom
-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 9/15/2022 15:43, Mikek wrote: >On another note: How does inductance change from say, a 1" long 0.30" diameter wire vs a 1" x 1"? square 0.30" thick?<
Found a calculator, 1" wire 21.1nH, 1" square plate 7.1nH.
?
|
>Why will the nichrome wire inductance be an issue?<
?I don't know, at 150MHz, every nH is 1Ω in series with the winding of the drive transformer.
1" of 30 gauge wire is 15.2nH
?If we go by the T68-2 50T Injection Transformer that Guido ON7CH presented, that should have a 0.02Ω output impedance,
50Ω input, 50 to 1 turns ratio, 2500 to 1 impedance ratio, 50/2500 = 0.02Ω.
?I'm speculating that the 0.02Ω source with 15.2nH or 15Ω of inductive reactance driving a 0.02Ω resistor,
isn't what you want to do, but I could easily have a poor or mistaken understanding and would be happy to be corrected.
????????????????????????????????????????? Mikek
P.S. What do you think of these Vishay resistors? 0.5nH to 5nH but no other specifics. I suspect the 0603 have the lowest inductance.
?https://www.vishay.com/docs/30122/wslp.pdf
|
Why will the nichrome wire inductance be an issue? The
measurement is the ratio of the voltage measured by the
VTVM at the inductor-capacitor junction and the voltage
drop across the precision resistor.
|
Thanks, Mikek!
--Cheers,
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 9/15/2022 16:13, Mikek wrote:
toggle quoted message
Show quoted text
>I'm curious where you found that calculator.<
??????????????????????????????? Mikek
_._,_._
|
>I'm curious where you found that calculator.<
??????????????????????????????? Mikek
|
That brings up the question, "What is the inductance of the precision resistor and the nichrome wire?
My thinking is they had to have a lot of heat to develop the current required to drive the meter.
See diagram.
We have opamps to give us all the gain we need. I did some figuring, a 10*C increase in temp will cause a 400mv change in a type K thermocouple.
A 0.125" long by 11.6 mill trace of 1 oz copper will rise 10*C from ambient with 1 amp flowing.
A 1" by 1", 1oz copper pcb will have about 7nH (I think that's high compared to the inductance of the precision resistor and the nichrome wire, but I don't know?)
If you etch it to have a 0.125 x 11.6 mill trace in the middle, the inductance will increase. the concept would be to put the thermocouple in the middle of that 0.125" trace,
spot weld as in the prc68 webpage in my last post.
?Here is a drawing of my thinking, ( I drew most of it so I would understand what the circuit is)
|
I'm curious where you found that calculator. I would've guessed
something a bit over 10nH for the plate, based on scaling the value
for the wire. Not a huge difference, but I'm curious to see what
formula that calculator is using for the square plate.
-- Cheers,
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 9/15/2022 15:43, Mikek wrote:
toggle quoted message
Show quoted text
>On another note: How does
inductance change from say, a 1" long 0.30" diameter wire vs a
1" x 1"? square 0.30" thick?<
Found a calculator, 1" wire 21.1nH, 1" square plate 7.1nH.
|
>On another note: How does inductance change from say, a 1" long 0.30" diameter wire vs a 1" x 1"? square 0.30" thick?<
Found a calculator, 1" wire 21.1nH, 1" square plate 7.1nH.
|
As far as the correct thermocouple, I have found nothing in Boonton (HP) notes to indicate what
the type was. Given that the wire reaches 1600° F nominal, I suspect if a standard thermocouple
"Type" was selected, it would have been the Type N which measures from 650° C to 1260° C
(1200° F to 2300 °F).
Boonton accounted for variances in the meter measuring the Nichrome wire temperature with
resistors in series with the wires to the meter that connected the thermocouple output. The meter
as I understand is in the 100 ?A range. The compensating resistor value was split and two equal
value resistors used, one resistor in each meter lead.
Also keep in mind, the temperature of the precision resistor is not being measured. When
calibrated at the factory, 1 Amp DC was injected into the input of the thermocouple sensor
assembly. With no inductor on the terminals, the nichrome heating wire current only flows to
the 20 milliOhm precision resistor. E=IR thus 1 Amp X? 0.02 Ω = 20 milliVolt.? Boonton engi-
neers used a precision lab quality method to determine the voltage across the precision
resistor. It does not matter if you use RF or DC current in the lashup. 1 Amp DC produces the
same voltage across the resistor as does 1 RMS Amp of RF. Both produce the same power
dissipation in a resistor and that 1 Amp of current DC or RF will produce a voltage drop of 20
millVolt DC or RMS.
The 260 was designed before I was born and I am 71 years old. Thus I am not aware of what
choices Boonton had for resistors in the day. What I do know is, their scientists and engineers
went to a lot of trouble to minimize the precision resistor inductance.? Pete Olin who worked for
Boonton in New Jersey, explained that the precision resistance is obtained with a thin layer of
platinum applied to a ceramic disc. He stated the precision resistors were often hand ground
with a very fine abrasive to bring the resistance down to the desired 20 milliOhm. The catch
when grinding the resistor was the conducting platinum layer removal had to be consistent
across the surface as variance in the thickness introduced inductance that caused errors across
the operating frequency.
Given the attention to detail in producing the precision resistor, I do not think the resistor is the
limiting factor in operational frequency range of the 260. Nor do I believe that the inductance
in the nichrome wire is coming into play. If anything, I suspect it is the length of connections where
inductors and capacitors under test are connected. The VTVM in the Q-Meter may also add to
the problem with its rapid rolloff approaching 50 MHz. If I find a 260 with a blown thermocouple,
I plan to connect the precision resistor up to a network analyzer and see just how high in frequency
the resistor can be utilized before the series inductance and stray capacitance become significant
enough to impact measurement accuracy. My SWAG is that the resistor can be used well up
beyond 150 MHz.? But that is just a SWAG.
Regards
Chuck
|
For those wanting to see the inside of the 260A 'resistance wire/thermocouple' assembly, this webpage has a repair of one.
?? Click on "thermocouple repair" in the index at the beginning.
He used a k type thermocouple, it didn't work out exactly correct, but, looks like a nice starting place if you want to use this method
to set drive current. I say it didn't work out exactly correct, that was for the 260A, for a new design, well, 'design' around the thermocouple output.
Interesting that he capacitive discharge welded the thermocouple to the resistance wire.
Anyone know a cheap source of just thermocouple junctions? Don't need the long wire or connector.
?On another note: How does inductance change from say, a 1" long 0.30" diameter wire vs a 1" x 1"? square 0.30" thick?
|
Re: Tektronix scope bandwidth?
The vertical amplifier specs for the Tek 1480 waveform monitor were, frequency response; 50KHz – 5MHz ± 0.5% (or ± 0.043dB), and for amplitude on the 1V range; ± 3mV (or ± 0.026dB). ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Eric
Sent: Wednesday, 14 September 2022 11:34
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] Tektronix scope bandwidth?? Also one place that Tek over speced their bandwidth that drive other vendors crazy was in the probes. A 100Mhz Tek probe can be used to 100Mhz with no roll off this is not true of all probes as a 100Mhz probe on a 100Mhz scope could lower the system bandwith of the combination to something less than 100Mhz ? Eric ? ? The +/- 1 dB was back in the Tek 453 scope days. ? Paul, W8AEF ? ? I've never heard that. And I've measured the bandwidth of many a 'scope over the the last 40 years, always finding it to be -3 dB very close to the rated BW, and conforming to BW = .35/RT.
-Gary NA6O
|
Re: "Analogue" indication on Oled display
To be very specific, an F767 Nucleo board with an S1D13517
graphics chip (mapped as 2 locations, 16 bits of memory mapped
data, but static RAM, so the timing could be controlled).?
What didn't work, a dynamic RAM using the FMC memory controller.?
The timing wasn't as flexible, and I suspect that the lead lengths
(which go all over the Nucleo board) were much too long.?
Never got that to work.?
On the other hand, the SPI inexpensive displays (and even SPI
graphics chips) work just fine, even on Nucleo boards.? That's a
viable option for projects.? OLED displays are even slower in
communications.?
Harvey
On 9/13/2022 10:57 PM, saipan59 (Pete)
wrote:
toggle quoted message
Show quoted text
On Tue, Sep 13, 2022 at 12:09 PM, Harvey White wrote:
I need to add some drawbacks to the eval boards
That's fair. For me, I have not had an issue so far. The gadgets I
tend to build do not include any truly high-speed buses, where a
couple inches of wire would be a problem.
I did build a Multi-Channel Analyzer (a device that processes
pulses from a photo-multiplier tube, resulting from ionizing
radiation - a really interesting sub-hobby BTW!) based around a
T.I. eval board, but my hand-wired custom board really took care
of the critical stuff, so the MCU only had to process 'buffered'
signals.
Before retiring from HP in 2017, I owned designs that included
SAS-3 signals - but the design requirements become so regimented
that there wasn't much opportunity for me to break it (although on
one proto build, I DID break it by messing up the pinout on a
backplane connector...Whoops).
Pete
|
Re: "Analogue" indication on Oled display
On Tue, Sep 13, 2022 at 12:09 PM, Harvey White wrote:
I need to add some drawbacks to the eval boards
That's fair. For me, I have not had an issue so far. The gadgets I tend to build do not include any truly high-speed buses, where a couple inches of wire would be a problem. I did build a Multi-Channel Analyzer (a device that processes pulses from a photo-multiplier tube, resulting from ionizing radiation - a really interesting sub-hobby BTW!) based around a T.I. eval board, but my hand-wired custom board really took care of the critical stuff, so the MCU only had to process 'buffered' signals. Before retiring from HP in 2017, I owned designs that included SAS-3 signals - but the design requirements become so regimented that there wasn't much opportunity for me to break it (although on one proto build, I DID break it by messing up the pinout on a backplane connector...Whoops). Pete
|
Re: Tektronix scope bandwidth?
Also one place that Tek over speced their bandwidth that drive other vendors crazy was in the probes. A 100Mhz Tek probe can be used to 100Mhz with no roll off this is not true of all probes as a 100Mhz probe on a 100Mhz scope could lower the system bandwith of the combination to something less than 100Mhz ? Eric ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Paul via groups.io
Sent: Tuesday, September 13, 2022 5:37 PM
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] Tektronix scope bandwidth?? The +/- 1 dB was back in the Tek 453 scope days. ? Paul, W8AEF ? ? I've never heard that. And I've measured the bandwidth of many a 'scope over the the last 40 years, always finding it to be -3 dB very close to the rated BW, and conforming to BW = .35/RT.
-Gary NA6O
|
Re: Tektronix scope bandwidth?
The +/- 1 dB was back in the Tek 453 scope
days.
?
Paul, W8AEF
?
toggle quoted message
Show quoted text
From: [email protected]
[mailto:[email protected]]
On Behalf Of Gary Johnson via
groups.io
Sent: Tuesday, September 13, 2022
11:16 AM
To: [email protected]
Subject: Re: [Test Equipment
Design & Construction] Tektronix scope bandwidth?
?
I've never heard that. And I've measured the bandwidth of many a 'scope
over the the last 40 years, always finding it to be -3 dB very close to the
rated BW, and conforming to BW = .35/RT.
-Gary NA6O
|
Re: Tektronix scope bandwidth?
I've never heard of that, either. The manuals of that period all use
the conventional 3dB figure.
Now, if the statement had been "Tek spec'd in-band flatness to a 1dB
error band" out to where it finally rolls off, sure. But to specify
the band width as the 1dB roll off point would have
driven Tek's marketing folks crazy, trying to explain to prospective
buyers why a lower bandwidth number was actually better.
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 9/13/2022 11:15, Gary Johnson via
groups.io wrote:
toggle quoted message
Show quoted text
I've never heard that. And I've measured the bandwidth of many a
'scope over the the last 40 years, always finding it to be -3 dB
very close to the rated BW, and conforming to BW = .35/RT.
-Gary NA6O
_._,_._,_
|
Re: Tektronix scope bandwidth?
I've never heard that. And I've measured the bandwidth of many a 'scope over the the last 40 years, always finding it to be -3 dB very close to the rated BW, and conforming to BW = .35/RT.
-Gary NA6O
|
Re: "Analogue" indication on Oled display
I need to add some drawbacks to the eval boards (I think,
regardless of manufacturer, which also includes Arduino).
If most of what you do is I2C, SPI, parallel and the like, the
signals can be slow enough that interconnections and lead lengths
do not really matter.? There are three zones, processor to off
board connector, connector(s), and whatever's on your board.? Of
the three, only on your board is there any choice.
For the signals that are slow or can be made so, you can tweak
parameters to generally get it to work.
If, however, you are dealing with memory mapped chips (expansion
memory on ST micro and memory mapped graphics chips), then the
timing and lead length can be critical, and you may not have much
control over some of the signals.? This can cause malfunctions.
At this point, you may be forced into designing your own boards,
and I'd recommend 4 layer boards depending on the application.? At
100mm square, you could be paying about 7 or 8? USD for five of
them (depending on how you shop).
Considering the current design topic, none of this is too likely
to happen.? However, once your designs become more complicated,
this might become a factor to be considered.
(Been there, did that, have the boards that don't work).
Harvey
On 9/13/2022 1:31 PM, saipan59 (Pete)
wrote:
toggle quoted message
Show quoted text
On Tue, Sep 13, 2022 at 08:36 AM, Harvey White wrote:
I've done some display work, and I generally find that
the Arduino (at least the MEGA series) is too slow and has too
little memory to be useful for involved graphics.? However,
there's a U8xxxx library out there that seems to be a standard
for arduino projects.? I've transitioned to the STM32 series a
while ago.
I would add, for those that don't know, the Arduino ecosystem is
oriented towards being relatively easy and educational and such.
But when performance is important, it's better to use the MCU
chips "more directly", meaning (typically) code written in C,
using the vendor's development GUI (they all tend to be similar),
and taking advantage of the vendor's own driver libraries.?
Note that for nearly all applications, any of the major MCU
vendors can get the job done. They have dozens of chips, a bunch
of Eval Boards, code libraries, tutorials, etc.
I think that the STM32 series is good, but I've never used it.
Over the years I've implemented many dozens of apps for MCUs (in
my 'real job' and as a hobby), for a long time using Microchip
parts, then in more recent years T.I. Now retired, I still do a
lot of hobby projects using T.I. Tiva, MSP430, and MSP432 -series
parts. Any more, I always use an Eval board as the basis of the
HW. Most of the boards are less than US$20, have an on-board USB
programmer, have a bunch of 0.1" pins to connect to, and sometimes
other useful parts. I've made custom PCBs in the past, but it no
longer feels like a good investment of my time.
Pete
|
Brian
saipan59 (Pete)