to -
ss his
-es
ee
-nt
zing
tions like this.
other uses.
ad on ebay and sent to a local
er.
DVM
ofer
or DC
nd
Buy it.
Did just that in getting my Ph.D.
Buy it.
Buy it.
That is supposed to be difficult?
.... ooops got to measure the frequency to test the VCXO, making
Buy it.
Here we go again. MooseFET is nearly as dumb as Rich Grise.
-- Bill Sloman, Nijmegen
Which are you buying the frequency standard or the accurately machined parts?
Which are you buying the frequency standard or the Laser? The Laser you need is not off the self.
Yes the one you need in a frequency standard is not easy.
___
It screwed up because of total line length.
Silly question - if you could buy the frequency standard, there wouldn't be much point in setting up a non-governemnt standards lab.
But most of the bits you need to assemble it can be bought.
Why? I'd like to know why you think that.
-- Bill Sloman, Nijmegen
and I=20
voltage(v1)=20
and read=20
Error).
resistor and=20
-------------------------------------------------------------------------=
-----
temperature
require
while=20
elsewhere but=20
-------------------------------------------------------------------------=
-------
tried the
setup
-------------------------------------------------------------------------=
-------------
___
|\\|=20
|---|-\\=20
|-----|+/
|/|
-------------------------------------------------------------------------=
-------------
as
too.
-------------------------------------------------------------------------=
-------------
=20
resistor.
resistor=20
It=20
-------------------------------------------------------------------------=
-------------
------------------
procedure.
------------------
Added diff amps are un-needed and unwanted. Use analog mux directly from the sense terminal pairs from each resistor. Also, unless you have gain in the first stage of your diff amp all you will do is add noise. The source impedance is low enough that buffers are not needed nor wanted.
g,
But that wasn't the question I asked.
The few you can't buy are the important ones.
In the common circuit for a frequency standard, you need to modulate the VCXO. The loop locks to a tiny fraction of the line width. Any even order nonlinearity in the VCXO shows up as a frequency offset. In the short term, the noise on the output of the standard is the noise of the VCXO. You need to have a very linear and low noise VCXO. The servo loop of the standard only starts to take out the noise at frequency offsets under 1KHz.
rote:
and I
tage(v1)
and read
.r and
-------------
perature
require
while
ere but
---------------
d the
tup
-------------------
| =A0 =A0 =A0 =A0 =A0 |
=A0 | =A0 =A0 =A0 =A0 =A0 |
=A0 =A0 |\\| =A0 |
'-----|-\\ =A0 | =A0 ___ =A0 =A0 =A0 =A0 =A0 =A0 =A0 ___
=A0 =A0 =A0 =A0 |
-----|+/ =A0 =A0 =A0 =A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0 =A0|/| =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 |\\|
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|---|-\\
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0>-
|-------- | =A0 =A0 =A0 =A0 |-----|+/
| =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 |/|
=A0 =A0 | =A0 |\\| =A0 | =A0 =A0 =A0 =A0 |
=A0 =A0 |---|-\\ =A0 | =A0 ___ =A0 |
=A0 =A0 =A0 | =A0>- | -|___|- |
=A0 =A0 .---|+/ =A0 =A0 =A0 =A0 =A0 =A0 |
=A0 | =A0 |/| =A0 =A0 =A0 =A0 =A0 =A0.-.
=A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| |
=A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| |
=A0 =A0 =A0 =A0 =A0'-'
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =3D=3D=3D
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 GND
-------------------
s .-----------------
sistor.
tor
It
-----------------
l------------------
re.
------------------
Also parts like the OP-27 are not a good choice here. It is likely to add 0.1mV of offset voltage. You need more like "none"
voltage(v1)
read
------------------------------------------------------------------------------
temperature
require
while
but
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------------
___
--------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------
So, a "zero crossing" op amp?
I
voltage(v1)
and read
and
------------------------------------------------------------------------------
temperature
require
while
but
--------------------------------------------------------------------------------
the
--------------------------------------------------------------------------------------
___--------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------
resistor.
--------------------------------------------------------------------------------------
"Zero drift" chopamp. But he doesn't need a diffamp at all, just a differential-input delta-sigma ADC.
John
ranges and I
changes.
read voltage(v1)
resistor and read
Error).
resistor and
-------------------------------------------------------------------------=
-----
a temperature
you require
problem. while
elsewhere but
Tc.
-------------------------------------------------------------------------=
-------
tried the
your setup
-------------------------------------------------------------------------=
-------------
=A0 | =A0 =A0 =A0 =A0 =A0 |
=A0| =A0 =A0 | =A0 =A0 =A0 =A0 =A0 |
=A0 | =A0 =A0 |\\| =A0 |
=A0 '-----|-\\ =A0 | =A0 ___ =A0 =A0 =A0 =A0 =A0 =A0 =A0 ___
=A0 =A0 =A0 =A0 =A0 |
=A0'-----------|+/ =A0 =A0 =A0 =A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0 =A0|/| =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 |\\|
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|---|-\\
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0>-
=A0|-------- | =A0 =A0 =A0 =A0 |-----|+/
=A0| =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 |/|
=A0 =A0 | =A0 |\\| =A0 | =A0 =A0 =A0 =A0 |
=A0 =A0 |---|-\\ =A0 | =A0 ___ =A0 |
=A0 =A0 =A0 =A0 | =A0>- | -|___|- |
=A0 =A0 .---|+/ =A0 =A0 =A0 =A0 =A0 =A0 |
=A0 =A0 | =A0 |/| =A0 =A0 =A0 =A0 =A0 =A0.-.
=A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| |
=A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| |
=A0 =A0 =A0 =A0 =A0 =A0'-'
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =3D=3D=3D
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 GND
-------------------------------------------------------------------------=
-------------
well as
good, too.
-------------------------------------------------------------------------=
-------------
they are
film
amp's resistor.
lower
resistor
problem. It
-------------------------------------------------------------------------=
-------------
the
current
resistance will
------------------
one
Ibe
different
think
but
used
procedure.
but
------------------
directly
you
needed
Poxy hell. Are you going off on one of your monomanias again?
and I
voltage(v1)
and read
and
------------------------------------------------------------------------------
temperature
require
while
elsewhere but
--------------------------------------------------------------------------------
the
setup
--------------------------------------------------------------------------------------
___ >---------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------
resistor.
resistor
--------------------------------------------------------------------------------------
procedure.
Can you suggest a better way to digitize, with high precision, the dc voltage drop across a shunt?
Tell us about it.
John
ranges and I
changes.
read voltage(v1)
resistor and read
Error).
resistor and
-------------------------------------------------------------------------=
-----
have a temperature
precision you require
problem. while
elsewhere but
Tc.
-------------------------------------------------------------------------=
-------
you'd tried the
your setup
-------------------------------------------------------------------------=
-------------
=A0 =A0 | =A0 =A0 =A0 =A0 =A0 |
=A0| =A0 =A0 | =A0 =A0 =A0 =A0 =A0 |
=A0 | =A0 =A0 |\\| =A0 |
=A0 =A0 '-----|-\\ =A0 | =A0 ___ =A0 =A0 =A0 =A0 =A0 =A0 =A0 ___
=A0| =A0 =A0 =A0 =A0 =A0 |
=A0'-----------|+/ =A0 =A0 =A0 =A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0 =A0 =A0|/| =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 |\\|
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|---|-\\
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0>-
=A0 =A0|-------- | =A0 =A0 =A0 =A0 |-----|+/
=A0 =A0| =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | =A0 =A0 |/|
=A0 =A0 =A0 | =A0 |\\| =A0 | =A0 =A0 =A0 =A0 |
=A0 =A0 =A0 |---|-\\ =A0 | =A0 ___ =A0 |
=A0 =A0 =A0 =A0 | =A0>- | -|___|- |
=A0 =A0 =A0 .---|+/ =A0 =A0 =A0 =A0 =A0 =A0 |
=A0 =A0 | =A0 |/| =A0 =A0 =A0 =A0 =A0 =A0.-.
=A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| |
=A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| |
=A0 =A0 =A0 =A0 =A0 =A0'-'
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =3D=3D=3D
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 GND
-------------------------------------------------------------------------=
-------------
well as
good, too.
-------------------------------------------------------------------------=
-------------
they are
metal film
amp's resistor.
lower
each resistor
problem. It
-------------------------------------------------------------------------=
-------------
they
=A0Redo the
current
resistance will
------------------
place one
then I
to be
just
different
think
non-linearity but
I used
procedure.
tables but
------------------
directly
you
add
needed
to
Given choice, i would use ratiometric methods. I can get the same or better speed and the same or better resolution with better accuracy. Plus i get it all in one conversion instead of 4.
What fuzzy blather.
John
Have something to add? Share your thoughts — no account required.
Ask the community — no account required