Assigned value for fixed single-value devices

When you use a fixed single-value standard, what value do you use as the reference?

  • The most recent certificate value and uncertainty

    Votes: 1 33.3%
  • The mean of the most recent few values, and the standard deviation of the mean (how many?)

    Votes: 1 33.3%
  • The mean of all values in the device's history, and the standard deviation of the mean

    Votes: 0 0.0%
  • Values taken from a SPC chart of the device history

    Votes: 0 0.0%
  • The manufacturer's original certified value and uncertainty

    Votes: 0 0.0%
  • The manufacturer's nominal value and uncertainty specification

    Votes: 0 0.0%
  • Some other value (please explain)

    Votes: 0 0.0%
  • I don't know

    Votes: 1 33.3%
  • I don't have any fixed single-value standards

    Votes: 0 0.0%

  • Total voters
    3
  • Poll closed .
G

Graeme

#1
Some calibration standards are fixed devices with a single nominal value. Examples are DC voltage sources, standard resistors and so on. When calibrated, the report should include the measured value and the calibration uncertainty.

There are several methods of determining the reference value to be used (the "assigned value"). I need to develop a defined process for my lab, but first I would like to benchmark what others are doing.

The poll lists a number of different ways I can think of, and I am interested in other ways that may be used. Also, of course, the method may vary based on the nature of the device.

It would also be interesting to discuss the good and bad points of various methods.

(I hope this works - it's my first attempt at a poll!)

 
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G

Graeme

#3
Marc said:
What? No takers on this?
Maybe I should vote myself -- but I don't want to risk biasing it.
Maybe it's because this is summer holiday month in Europe. :biglaugh: But hey, I'm headed back to England at the end of the week for my summer holiday ...
 
R

Ryan Wilde

#4
Graeme,

Actually, it varies. For things like DC Voltage Sources and standard resistors, the variation over time is basically linear, and I use the value that it "should" be today with the uncertainty of that trend. For things like gage blocks, which don't tend to have a linear degradation, I use the last calibration value with uncertainty.

Ryan
 
G

Graeme

#5
Is being a generalist a specialty?

Ryan Wilde said:
Graeme,

Actually, it varies. For things like DC Voltage Sources and standard resistors, the variation over time is basically linear, and I use the value that it "should" be today with the uncertainty of that trend. For things like gage blocks, which don't tend to have a linear degradation, I use the last calibration value with uncertainty.

Ryan
Thanks, Ryan - being an electronics person I had not given much thought to the behavior of physical/dimensional standards. If I had thought of it I should have checked to see if the poll engine could handle multiple responses (pick the top 3, for example). But I suspect that trying to cover all possible combinations would overload its ability.

On using "today's" estimated value and uncertainty - I have a couple of questions.
  1. How does a typical bench technician get the values to use?
  2. If you use an automated measurement system, how does that system get the current estimated value of the standard?
Thanks again
 
R

Ryan Wilde

#7
Graeme said:
On using "today's" estimated value and uncertainty - I have a couple of questions.
  1. How does a typical bench technician get the values to use?
  2. If you use an automated measurement system, how does that system get the current estimated value of the standard?
Thanks again
All devices that show a linear trend are actually marked with a label on the unit showing that trend, usually in "x ppm/yr", with the corresponding uncertainty of the trend on the label. The technician takes:

(the last calibrated value)+((# days since last cal/365)*(ppm/yr trend))

For automated measurement systems, we write into the datafile for the standard the trend and have the software do the calculations for us, but we normally write our own software with that in mind. We always make accuracy/actual value files separate from the program, and always in a plain text format for ease of editing when necessary. The datafiles are stored in a protected folder to ensure that they aren't tampered with.

Ryan
 
L

lhiga

#8
Fixed Value Standards

On using "today's" estimated value and uncertainty - I have a couple of questions.
How does a typical bench technician get the values to use?
If you use an automated measurement system, how does that system get the current estimated value of the standard?

Graeme,

We project the value monthly on the certificate. On our automated system the technician makes a change to the reference number at the beginning of the month.
 
G

Graeme

#9
Thank you all!

This poll is closed now, and I want to thank everyone for their input. Now I have to find the time to hide out with the data, study it and see what comes out. I will put results here when available, hopefuly by the end of the year.

THANK YOU :thanx: :applause: :agree1: :thanx: to everyone who voted and/or posted.
 
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