Philips PM6654 frequency counter

[davorin]

Looking at the Philips PM6654 datasheet it is unclear to me what resolution it has at lower frequencies....

So can it actually show if a frequency is 1.0000001 or 1.0000002 Hz?

[dom0]

(2.5 x 10^-7 s x f) / gate time

So for 1 Hz the resolution is about 25 mHz (at 10 meas/s).

Mind you, these are very good counters and where the highest-end models Philips made for quite some time - especially considering their 2 ns time base.

[davorin]

So who is besides Fluke/Philips the best frequency counter nowadays?

Seems counters have vanished from the market...or I didn't look at them closely lately...

Hmm...25mHz.....I would rather go with 25uHz or less if that's doable... (o;

[edpalmer42]

How about nanoHz?

Here are the readings from my counters.

Racal Dana 1991/1992 measures 1 Hz as
1000.XXXXXXe-3 with a 1 second gate time (measurement takes 2 seconds) or
1000.XXXXXXXe-3 with a 10 second gate time

Agilent 53131A measures 1 Hz as
1.XXX,XXX,XXX,X with a 1 second gate time (measurement takes 5 seconds) or
1.XXX,XXX,XXX,XX with a 10 second gate time

Fluke/Philips PM6681 measures 1 Hz as
1.XXXXXXXXX with a 1 second gate time (measurement takes 5 seconds) or
1.XXXXXXXXX with a 10 second gate time (i.e. same reading)

Some counters measure period faster and/or more accurately than frequency.  Odd, but true.

Ed

[tautech]

So who is besides Fluke/Philips the best frequency counter nowadays?

Seems counters have vanished from the market...or I didn't look at them closely lately...

Hmm...25mHz.....I would rather go with 25uHz or less if that's doable... (o;

Siglent AWG's, the SDG1000 and 5000 series are rated 100mHz~200MHz as a counter.
http://www.siglentamerica.com/pdxx.aspx?id=145&T=2&tid=16
In the "documents" window, you'll find the datasheet and manuals.

[Robert763]

Hmm,
The Siglent AWGs hardly qualify as counters, it's just a utility function. Only 6 digit resolution. The two big players since Fluke dropped the PM66xx range are Keysight and Stanford Research Systems (SRS).  The SRS 620 costs about $5000, The Keysight 53131A costs about $3000. The PM6654 actually compares well to these current models. Modern sub 500MHz counters use reciprocal counting were they count the reference for the period of the signal. This means fo a 1Hz signal and 10MHz refernce you can only get 8 digit resolution. There are two different ways around this. One is to use a higher reference, the other is an analog interpolator the measures how far after the last reference edge the stop signal arrived. The 53131 (and famous predecessor 5370A/B considered on of the best ever) use interpolation, the PM6654 uses a 500MHz reference (multiplied from 10MHz.
 

[dom0]

There's also Spectracom. They acquired Pendulum AB which was a spin-off of Fluke's frequency measurement business, which was acquired from Philips during their T&M merger. Although it would seem that the Pendulum business has little priority for Spectracom.