Re: [volt-nuts] Traveling Standards - Measuring Protocol
Bob
First I'd like to say that what your doing is a great idea and could be a
great benefit to the Volt nut group.
Now for some comments that I hope you will find useful to get the most from
this exercise.
I'm still hoping you will post more details and if need be get suggestions
for the measurement that YOU should make before sending the TS out.
When doing short term stability testing better to do it at a Higher
resolution than 1.7 PPM / count.
One way to do that is to put your 6 digit voltmeter on the 1V or better yet,
the 0.1V range and measure the difference between the Device you're testing
and
a similar stable non-effected voltage such as a second device of the same
type that is not being subject to the things you're testing for.
Then taking into consideration that noise measurements are the RMS sum of
the two devices and Drift measurements are the Difference between devices,
it is possible to greatly increase the accuracy of the measurements.
Also very useful to measure the actual Temperature Coefficient of the
devices so that the temperature readings have more meaning.
When evaluation precision voltage references,
I find it very helpful to make a High Resolution strip chart recording, be
it Analog or Digital,
Preferable showing Both temperature and voltage.
For an example of how I get much better than 0.1 PPM resolution using 50
year old technology,
See attached plot comparing two 10 volt devices, using a slow, dual channel
analog Rustrak recorder and Fluke 845A/B null meter
Just my two cents worth to the bigger picture.
It is hard to properly evaluate a precision Voltage source unless you first
know the measurement uncertainties 'aka noise' including any Temperature
Coef.
AND if the temperature coef is known and not zero (over the measurement
temperatures), why not add a simple compensating voltage to reduce the
effect of temperature to insignificant levels?
ws
[volt-nuts] Traveling Standards - Measuring Protocol
Bob Smither smither at c-c-i.com
I guess it makes sense to define the set of measurements to be made on a
Traveling Standard and how those measurements are to be made. I have
put a draft protocol for making TS measurements here:
http://c-c-i.com/tsp
This is all pretty new to me, so I would appreciate any feedback from
the list members, especially those that have agreed to make measurements.
Thanks!
Bob Smither, PhD Circuit Concepts, Inc.
---=====
Also very useful to measure the actual Temperature Coefficient of the
devices so that the temperature readings have more meaning.
When evaluation precision voltage references,
I find it very helpful to make a High Resolution strip chart recording, be
it Analog or Digital,
Preferable showing Both temperature and voltage.
For an example of how I get much better than 0.1 PPM resolution using 50
year old technology,
See attached plot comparing two 10 volt devices, using a slow, dual
channel
analog Rustrak recorder and Fluke 845A/B null meter
Tempco measurement will be essential for the MAX6350.
For the LM199 I have made the experience that over a
10 to 40 degree (celsius) temperature range there will be
around 1 ppm of change. Of course its better to know
the exact values. So its easier to trace back the current measurement.
First picture MAX6250A (which is similar to the MAX6350)
used as voltage reference of a LTC2400 measuring
my LM399 #2 with a LTC1043 based precision voltage divider
over temperature range 10 - 40 degree celsius.
Y-axis is 2:1 divided voltage in mV.
You can clearly see the hysteresis of the plastic device.
And you can see a "hysteresis jump" near 39 degrees of around 1 ppm.
Attached you see a plot of my LM399 #2 over temperature
as difference to my LM399 #1 at room temperature.
recorded is
red: difference voltage in mV LM399 #1 - LM399 #2
light blue: same but averaged to get the noise out
green: environment temperature of LM399 #2 housing
dark blue: within LM399 #2 housing
yellow: environment temperature of LM399 #1
so the change is around 7uV when regarding the averaged value.
and most of the "tempco" seems to be off the temperature
gradient (thermo voltages) and not from the actual temperature.
With best regards
Andreas
WarrenS wrote:
Bob
First I'd like to say that what your doing is a great idea and could be
a great benefit to the Volt nut group.
Now for some comments that I hope you will find useful to get the most
from this exercise.
I'm still hoping you will post more details and if need be get
suggestions for the measurement that YOU should make before sending the
TS out.
Good point - I am very open to suggestions about what I should do to
characterize the TS before it is shipped around.
When doing short term stability testing better to do it at a Higher
resolution than 1.7 PPM / count.
One way to do that is to put your 6 digit voltmeter on the 1V or better
yet,
the 0.1V range and measure the difference between the Device you're
testing and
a similar stable non-effected voltage such as a second device of the
same type that is not being subject to the things you're testing for.
Then taking into consideration that noise measurements are the RMS sum
of the two devices and Drift measurements are the Difference between
devices,
it is possible to greatly increase the accuracy of the measurements.
Also very useful to measure the actual Temperature Coefficient of the
devices so that the temperature readings have more meaning.
When evaluation precision voltage references,
I find it very helpful to make a High Resolution strip chart recording,
be it Analog or Digital,
Preferable showing Both temperature and voltage.
For an example of how I get much better than 0.1 PPM resolution using 50
year old technology,
See attached plot comparing two 10 volt devices, using a slow, dual
channel analog Rustrak recorder and Fluke 845A/B null meter
Just my two cents worth to the bigger picture.
It is hard to properly evaluate a precision Voltage source unless you
first know the measurement uncertainties 'aka noise' including any
Temperature Coef.
AND if the temperature coef is known and not zero (over the measurement
temperatures), why not add a simple compensating voltage to reduce the
effect of temperature to insignificant levels?
Hi Warren,
Thanks for the great suggestions! I will follow up on them as I have
time. Looks like my plate is pretty full on this project:
- Repackage it to avoid being visited by the Gestapo :-).
- Wire up a second LM199AH for the offset measurement.
- Measure the TC of both LM199AHs using difference technique.
- Measure the TC of the MAX6350 using difference technique.
I will be working towards the above. In the meantime I will post some
very preliminary TC measurements (not high resolution) when they are
completed.
Best regards,
Bob Smither
What type of averaging did you do for the light blue trace?
Regards,
mitch
----- Original Message -----
From: "Andreas Jahn" Andreas_-_Jahn@t-online.de
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Wednesday, September 07, 2011 1:45 PM
Subject: Re: [volt-nuts] Traveling Standards - Measuring Protocol
Also very useful to measure the actual Temperature Coefficient of the
devices so that the temperature readings have more meaning.
When evaluation precision voltage references,
I find it very helpful to make a High Resolution strip chart recording,
be
it Analog or Digital,
Preferable showing Both temperature and voltage.
For an example of how I get much better than 0.1 PPM resolution using 50
year old technology,
See attached plot comparing two 10 volt devices, using a slow, dual
channel
analog Rustrak recorder and Fluke 845A/B null meter
Tempco measurement will be essential for the MAX6350.
For the LM199 I have made the experience that over a
10 to 40 degree (celsius) temperature range there will be
around 1 ppm of change. Of course its better to know
the exact values. So its easier to trace back the current measurement.
First picture MAX6250A (which is similar to the MAX6350)
used as voltage reference of a LTC2400 measuring
my LM399 #2 with a LTC1043 based precision voltage divider
over temperature range 10 - 40 degree celsius.
Y-axis is 2:1 divided voltage in mV.
You can clearly see the hysteresis of the plastic device.
And you can see a "hysteresis jump" near 39 degrees of around 1 ppm.
Attached you see a plot of my LM399 #2 over temperature
as difference to my LM399 #1 at room temperature.
recorded is
red: difference voltage in mV LM399 #1 - LM399 #2
light blue: same but averaged to get the noise out
green: environment temperature of LM399 #2 housing
dark blue: within LM399 #2 housing
yellow: environment temperature of LM399 #1
so the change is around 7uV when regarding the averaged value.
and most of the "tempco" seems to be off the temperature
gradient (thermo voltages) and not from the actual temperature.
With best regards
Andreas
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----- Original Message -----
From: "Mitch Van Ochten" mitch@vincentelectronics.com
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Thursday, September 08, 2011 2:48 AM
Subject: Re: [volt-nuts] Traveling Standards - Measuring Protocol
What type of averaging did you do for the light blue trace?
Regards,
mitch
----- Original Message -----
From: "Andreas Jahn" Andreas_-_Jahn@t-online.de
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Wednesday, September 07, 2011 1:45 PM
Subject: Re: [volt-nuts] Traveling Standards - Measuring Protocol
Attached you see a plot of my LM399 #2 over temperature
as difference to my LM399 #1 at room temperature.
recorded is
red: difference voltage in mV LM399 #1 - LM399 #2
light blue: same but averaged to get the noise out
green: environment temperature of LM399 #2 housing
dark blue: within LM399 #2 housing
yellow: environment temperature of LM399 #1
so the change is around 7uV when regarding the averaged value.
and most of the "tempco" seems to be off the temperature
gradient (thermo voltages) and not from the actual temperature.
Hello,
the red curve is one measurement with an integration time of 1 minute.
(about 350 measurement values of LTC2400 ADC with 10-30uVpp
noise averaged giving around 2 uVpp for 1 minute integration time).
the light blue trace is the sliding average over 21 minutes of
the red curve.10 minutes before, current minute and 10 minutes after.
(so noise is reduced down to below 0.5uVpp).
Total measuremen time (x-Axis) is around 940 minutes.
with best regards
Andreas
Hello Warren,
to come back to your zener diode selections:
- do you have any source where the selection of zener diodes is described?
I have read on a german page that zeners are selected by
their "noise characteristic". And that the noise will show the long term
behaviour.
But its not described which kind of noise has an influence.
Is it broad-band noise? 0.1 to 10 Hz noise? or even the lower frequency
noise (which you have recorded on the strip chart recorder).
From the german link it is not clear wether the selection is
according to the value of the noise or the change before
and after pre-ageing.
And the bad news is that my LM399#1 which is drifting
much more than my LM399#2 has only about 50% of
0.1 to 10 Hz noise than the LM399#2.
By the way how do you make the plots?
Do you always record the difference of two similar devices to
compensate for the DC-Offset?
Has the strip chart recorder 1uV resolution or do you have
to add a pre-amplifier? (which one?).
The 10 second time constant: is it built in within the recorder
or external (low-ohmic / high ohmic resistor + what kind of capacitor)
with best regards
Andreas
----- Original Message -----
From: "WarrenS" warrensjmail-one@yahoo.com
To: volt-nuts@febo.com
Sent: Wednesday, September 07, 2011 6:36 PM
Subject: Re: [volt-nuts] Traveling Standards - Measuring Protocol
Bob
First I'd like to say that what your doing is a great idea and could be a
great benefit to the Volt nut group.
Now for some comments that I hope you will find useful to get the most
from
this exercise.
I'm still hoping you will post more details and if need be get suggestions
for the measurement that YOU should make before sending the TS out.
When doing short term stability testing better to do it at a Higher
resolution than 1.7 PPM / count.
One way to do that is to put your 6 digit voltmeter on the 1V or better
yet,
the 0.1V range and measure the difference between the Device you're
testing
and
a similar stable non-effected voltage such as a second device of the same
type that is not being subject to the things you're testing for.
Then taking into consideration that noise measurements are the RMS sum of
the two devices and Drift measurements are the Difference between devices,
it is possible to greatly increase the accuracy of the measurements.
Also very useful to measure the actual Temperature Coefficient of the
devices so that the temperature readings have more meaning.
When evaluation precision voltage references,
I find it very helpful to make a High Resolution strip chart recording, be
it Analog or Digital,
Preferable showing Both temperature and voltage.
For an example of how I get much better than 0.1 PPM resolution using 50
year old technology,
See attached plot comparing two 10 volt devices, using a slow, dual
channel
analog Rustrak recorder and Fluke 845A/B null meter
Just my two cents worth to the bigger picture.
It is hard to properly evaluate a precision Voltage source unless you
first
know the measurement uncertainties 'aka noise' including any Temperature
Coef.
AND if the temperature coef is known and not zero (over the measurement
temperatures), why not add a simple compensating voltage to reduce the
effect of temperature to insignificant levels?
ws
[volt-nuts] Traveling Standards - Measuring Protocol
Bob Smither smither at c-c-i.com
I guess it makes sense to define the set of measurements to be made on a
Traveling Standard and how those measurements are to be made. I have
put a draft protocol for making TS measurements here:
http://c-c-i.com/tsp
This is all pretty new to me, so I would appreciate any feedback from
the list members, especially those that have agreed to make measurements.
Thanks!
Bob Smither, PhD Circuit Concepts, Inc.
---=====
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