Stanford Research Systems will not supply a certified calibration

[graybeard]

I need to use a SRS785 for a project to measure low frequency noise.   The SRS785 and other SRS FFT model seem to be the only instruments I can find that will directly measure noise in the sub audio region.

I know it is possible to assemble a system to do this, but I do not have the time or budget for that.  The SRS FFTs do what I need out-of-the-box.

My issue is that Stanford Research Systems will not supply a certified calibration.   They say their calibrations are NIST traceable, but they do not have any form of calibration certification.

I must have a the unit ANSIZ540 certified calibration.

Is there a calibration house that can do a ANSIZ540 or 17025 certified calibration on this instrument?  Is there an alternative instrument that will directly measure sub audio noise levels?

[Tomorokoshi]

As for an alternative instrument, the HP / Agilent / Keysight 35670A is similar:

https://www.keysight.com/en/pd-1000001335%3Aepsg%3Apro-pn-35670A/fft-dynamic-signal-analyzer-dc-1024-khz?cc=US&lc=eng&lsrch=true&searchT=35670A

[graybeard]

We have a few of these that are reaching end-of-life.  I need an instrument I can buy new and I can get a ANSIZ540 or 17025 certified calibration for.

As for an alternative instrument, the HP / Agilent / Keysight 35670A is similar:

https://www.keysight.com/en/pd-1000001335%3Aepsg%3Apro-pn-35670A/fft-dynamic-signal-analyzer-dc-1024-khz?cc=US&lc=eng&lsrch=true&searchT=35670A

[maxwell3e10]

I been wondering for a long time why no one makes a newer version of these low-frequency spectrum analyzers. And also wondering how SRS manages to find 56 lbs of obsolete components to sell as new.

[coppercone2]

if its not broke and unpopular you don't need to fix it until you have competition

[DaJMasta]

Most modern audio analyzers have a DC coupling option, why not look towards some of those options?

Rohde & Schwarz UPV
NI PXI-4461
(I guess the SRS SR1 is out of the question...)
Keysight U8903B
Audio Precision APx series
Not as likely to get a cal for it, but there's the Prism Sound dScope III as well.

Any of those will have comprehensive FFT capability to a couple hundred kHz, it's not exactly a hardware problem these days in terms of processing, and if they have a DC so dedicated FFT analyzers are a lot less common.  Would it be acceptable to buy an instrument through a cal lab that could independently certify it even if the manufacturer doesn't?

[graybeard]

I been wondering for a long time why no one makes a newer version of these low-frequency spectrum analyzers. And also wondering how SRS manages to find 56 lbs of obsolete components to sell as new.

From talking with a sales "engineer" they have an inventory of per-assembled boards and front panels.  The chassis and power supply is common to many of the instruments they make.  Many of the instruments used a common display as well.  They now supply it with an LCD display since the CRTs are no longer made.   The quoted delivery time ARO is 2 weeks.

It has been available since 1995.

I am forbidden from using any instrument that requires a network connection.   IEEE-488 is still the best option available in most cases.   Unfortunately for me many new instruments are forgoing the IEEE-488 interface in favor of the much faster and cheaper network connection.

[graybeard]

Most modern audio analyzers have a DC coupling option, why not look towards some of those options?

Rohde & Schwarz UPV
NI PXI-4461
(I guess the SRS SR1 is out of the question...)
Keysight U8903B
Audio Precision APx series
Not as likely to get a cal for it, but there's the Prism Sound dScope III as well.

Any of those will have comprehensive FFT capability to a couple hundred kHz, it's not exactly a hardware problem these days in terms of processing, and if they have a DC so dedicated FFT analyzers are a lot less common.  Would it be acceptable to buy an instrument through a cal lab that could independently certify it even if the manufacturer doesn't?

Rohde & Schwarz UPV - a possibility but it is not calibrated to directly measure noise density
 
NI PXI-4461 - no for many reasons

(I guess the SRS SR1 is out of the question...) - maybe

Keysight U8903B - the manual makes it seem unlikely

Audio Precision APx series - definitely no for many reasons (I talked with them in December)

Ideally I want an instrument that directly measure noise density (V/Hz^½) down to 0.1 Hz.
Many of the audio analyzers do not measure this low in frequency and/or do not directly measure noise density.   I understand that noise density can be calculated from a power spectrum if the exact equivalent bandwidth is known, but it is much easier to deal with an instrument that directly reads noise density directly.

Would it be acceptable to buy an instrument through a cal lab that could independently certify it even if the manufacturer doesn't?- absolutely if the vendor was ANSIZ540 or 17025 certified.