Anyone using a Primary Frequency Standard?

[AlbertPaglinawan]

Particularly the Agilent 5071A Cesium Standard.

If you are using this, do you send this equipment for calibration?

If you do not send this for calibration (or you do not calibrate this equipment), can it still be traceable to NIST? Can you still use this unit as a standard? (After all, it is a Primary Frequency Standard!)

I asked coz I saw a scope of accreditation of a certain calibration lab and the frequency is traceable to a cesium beam and the traceability ends there because cesium beam does not need to be calibrated. (And the irony of it is they still claim the unit to be traceable to NIST because the unit was calibrated once, several years ago)

thanks in advance!

cheers!

 

[Ryan Wilde]

Well, this is a bit dicey, actually. The cesium beam itself is an intrinsic standard, and as such requires no calibration, because the laws of physics are above such trivial things as calibration.

Some people leave it at that, although I disagree with it strongly.

The cesium standards also have detectors and counters which discipline an oscillator, all of which are NOT intrinsic standards. Hence, Agilent DOES recommend recalibration every 12 months. Without calibration, I would say that their standard is not traceable, with one small caveat.

They may be doing regular inter-laboratory comparisons, which would make calibration redundant. If they are within their stated uncertainty, then calibration is not necessary.

The easiest way out is always a good GPS receiver. Great uncertainty, constant traceability (ours tracks and averages up to 8 satellites), much cheaper than a cesium standard.

Ryan

 

[Graeme]

My working assumption is that you already have a 5071 standard. If you don't, I would go along with Ryan and suggest getting a GPS-based system. That can give you frequency traceable to NIST (provided you regularly check the published difference logs) and with the right setup can also give you time-of-day traceable to the US Naval Observatory. (Useful if you work with navigation equipment.)

But I am assuming that you already have a 5071 standard and want to make it as good as possible. It has been a while since I used one, but I do remember a couple of things.

• First, there are certain checks (detailed in the manual) that should be done and logged regularly. (Various voltages, beam current, and so on.) If indicated, some adjustments may be needed to put everything back in tune.
• Second, plan on replacing the Cesium tube eventually. They do go bad, and they are not cheap.

Also, you may find it worthwhile to look at a service available from NIST -- the Frequency Measurement & Analysis Service. This service can be used with any kind of frequency reference you have in the lab, and can also be used with customer's equipment. NIST installs a rack of equipment at your site (including a GPS receiver, computer, software and more) - you only have to provide a dedicated phone line and a place to mount the GPS antenna. You can then check up to five frequency sources at a time (including your 5071), and this system is continually checking everything against NIST references. (There is a small fee, of course.)

A Cesium (or Caesium) beam standard is an intrinsic reference when it is working properly. I don't think it needs to be traceable to anything else. The key is to be able to assure that it is working properly. Using some other system, such as a GPS-disciplined Rubidium or Quartz oscillator or the NIST service (above), effectively compares it to a relatively large group of other standards. (Consider that every GPS satellite has two Cesium or Rubidium standards on board, and they are continually monitored by ground stations!) If the frequency difference is within limits, then it can be considered OK.