traceability

[CALSQUID81]

Is a monochromatic light considered to be an intrinsic standard, and if so what kind of traceability will it have?

[calibr8tor]

I'm not a light guy, but I would have to say no.  I would think any light source would change over time, and would have to be calibrated on an interval.

[mdbuike]

You could try here.. http://en.wikipedia.org/wiki/Monochrome 

But I've been calibrating fiber optics for the last seven years, and have found sources rarely drift more than one or two nanometers..not too much, the same for micrometer lights..in fact the USAF considers them NCR



Mike

[CalibratorJ]

Yeah, most military fiber sources are CNR (NCR), but the sources are set at a reference level before and during cal of a DUT (TI, etc) with a Lightwave Multimeter thingie (yes, such advanced metrology terms). Real pain to use as I am sure there are several alternatives out there that could be used as a true calibrated source (versus the old set a reference, disconnect, connect to DUT method).  But be honest, in the military at least, there just isn't much fiber (yet).

In 10+ years of doing calibration and repair, I think I can count on my fingers and toes how many fiber devices I have cal'd (pardon, I'm from Louisiana and live in Alabama- this is the ONLY accepted way of counting above 10) and several of them belonged to the Marines (the devices, not my toes). So, I am by no means an expert, but that just goes to show that there isn't much fiber in the military, well, at least the Army - or it is there, just not being tested (no big shocker there).

Good luck with the monochrome thing, might be easier to buy a meter.

[MIRCS]

Is a monochromatic light considered to be an intrinsic standard, and if so what kind of traceability will it have?

You talking about a light for measuring flatness?

If so, Yes and traceable to a physical constant/standard

[CALSQUID81]

yes I am referring to flatness measurements. Which physical constant/standard? Do I need to perform periodic checks on this item?

[michthai]

I sent your question to the light guru in the NASA Standards Lab at KSC.  See his answer below.

Monochromatic light can be generated many different ways; some are intrinsic; some are not.  For example, a monochromator can generate monochromatic light.  But the purity or bandwidth (just how mono-chromatic), depends on the slit widths, etc..  But more to the point, the accuracy of the wavelength of this light depends on the diffraction gratings, physical angles of turrets, stepper motor repeatability, etc.  The wavelength accuracy of a monochromator is generally calibrated via a spectral line lamp (mercury or krypton).  So the monochromator is not "intrinsic".

However, spectral line lamps (although they generate many different wavelengths and are not mono-chromatic) are intrinsic standards.  If you filter out the unwanted wavelengths, what you're left with is essentially monochromatic light that is intrinsically accurate.  Certain lasers are considered to be "intrinsic" (by some people) and are monochromatic (e.g.  a 632.8 nm iodine stabilized Helium Neon Laser).  The wavelength has been directly measured at NIST by comparison to a cesium oscillator and is accurate to a few parts in 106.

SO the short answer... "NO", not all monochromatic light is intrinsic; but some sources are.  It depends on the physical parameters that influence the wavelength.  If things like temperature, length, pressure, etc. affect the wavelength, then they are not intrinsic.  Spectral line lamps are the most intrinsic light sources I'm aware of, but require filtering to eliminate unwanted wavelengths (to become monochromatic).  Their wavelength (in a vacuum) is unaffected by most phycial parameters.  The wavelength is intrinsically defined or fixed by the atoms comprising the element (gas) inside the lamp.

Traceability is another issue.  For example, the CRC Handbook of Chemistry and Physics says that spectral line lamps are suitable for the calibration of optical spectrum analyzers, wavelength meters, etc and gives their uncertainty to be around ±0.0001 nm (or something like that).  This is how we calibrate OSA's.  But the general consensus is that even intrinsic standards should be compared to other intrinsic standards of other labs (including an NMI).  Even J-Volts are not by themselves "traceable" to an NMI, but are intrinsic.  They become "traceable" to an NMI only when they are involved in Inter-Laboratory Comparisons with other J-Volts (including NIST).  You might say that they are intrinsically traceable to fundamental constants of nature (but not to an NMI; unless involved in an ILC w/ NIST).  See attached file regarding the "traceability" of quantum and/or intrinsic standards.



Ask a simple question....  J

Paul R.



P.S.  The VIM definition of metrological traceability (see notes #1 and #7)... 



2.41 (6.10)

metrological traceability

property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty



Note 1 For this definition, a 'reference' can be a definition of a measurement unit through its practical realization, or a measurement procedure including the measurement unit for a non-ordinal

quantity, or a measurement standard.



Note 2 Metrological traceability requires an established calibration hierarchy.



Note 3 Specification of the reference must include the time at which this reference was used in establishing the calibration hierarchy, along with any other relevant metrological information about the reference, such as when the first calibration in the calibration hierarchy was performed.



Note 4 For measurements with more than one input quantity in the measurement model, each of the input quantity values should itself be metrologically traceable and the calibration hierarchy

involved may form a branched structure or a network. The effort involved in establishing metrological traceability for each input quantity value should be commensurate with its relative contribution to the measurement result.



Note 5 Metrological traceability of a measurement result does not ensure that the measurement uncertainty is adequate for a given purpose, nor that there is an absence of mistakes.



Note 6 A comparison between two measurement standards may be viewed as a calibration if the comparison is used to check and, if necessary, correct the quantity value and measurement uncertainty attributed to one of the measurement standards.



Note 7 The ILAC considers the elements for confirming metrological traceability to be an unbroken metrological traceability chain to an international measurement standard or a national

measurement standard, a documented measurement uncertainty, a documented measurement procedure, accredited technical competence, metrological traceability to the SI, and calibration

intervals (see ILAC P-10:2002).



Note 8 The abbreviated term "traceability" is sometimes used to mean 'metrological traceability' as well as other concepts, such as 'sample traceability' or 'document traceability' or 'instrument traceability' or 'material traceability', where the history ("trace") of an item is meant. Therefore, the full term of "metrological traceability" is preferred if there is any risk of confusion.

[MIRCS]

yes I am referring to flatness measurements. Which physical constant/standard? Do I need to perform periodic checks on this item?

It has to do with interference.  No you don't need to perform periodic checks on your light, just the optical flats.  It's just what they are, HeNe is 632.8nm, which equals 24.8uin, so half the of the wavelength is 12.4uin which is a standard for all who use most Interferometers.

van Keuren uses a Helium bulb which is 587.6nm, which is 23.13uin, which half is 11.565uin. 

I don't believe you need to have anything listed for the light itself. 

[mdbuike]

Yeah, most military fiber sources are CNR (NCR), but the sources are set at a reference level before and during cal of a DUT (TI, etc) with a Lightwave Multimeter thingie (yes, such advanced metrology terms). Real pain to use as I am sure there are several alternatives out there that could be used as a true calibrated source (versus the old set a reference, disconnect, connect to DUT method).  But be honest, in the military at least, there just isn't much fiber (yet).

In 10+ years of doing calibration and repair, I think I can count on my fingers and toes how many fiber devices I have cal'd (pardon, I'm from Louisiana and live in Alabama- this is the ONLY accepted way of counting above 10) and several of them belonged to the Marines (the devices, not my toes). So, I am by no means an expert, but that just goes to show that there isn't much fiber in the military, well, at least the Army - or it is there, just not being tested (no big shocker there).

Good luck with the monochrome thing, might be easier to buy a meter.

Well, the USAF has gotten heavy into fiber, laying out thier base communications with it, and putting it into thier aircraftm as it is more EMP proof, and lighter...I'm doing a lot of fiber, which is cool, I like my job    

Mike

[spanishfly25]

Some physical standards are acceptable as NIST traceable standards, a good example is the triple ice point for water to calibrate temperature. Monochromatic light sources are made with an element that only produces one wavelength. and that wavelength is dependable of the material use to make the light, unless the material changes the wavelength never going to change,  in a simple answer, yes the can be use as standards, they don't need recalibration and for traceability write physical standard