[time-nuts] Logging the grid frequency....

Tom Van Baak tvb at LeapSecond.com
Fri Feb 22 18:32:48 EST 2013


Bob,

You're right that conventional period, frequency, or universal counters have great difficulty measuring (timing) separate events that occur as fast as 60 Hz. A fine exception is the Pendulum CNT-90/91 which is a time-stamping universal counter. With a few simple GPIB commands, you get data on every rising/falling edge of an input signal. The resolution is 50 ps and the capture rate is 250k sps.

If anyone has been able to collect zero-deadtime per-cycle timing using, say, a HP 5370 or 53132 or SR620 I would be interested to know it was done. It might actually be possible, but I've not tried hard enough. The HP 5372A is another possibility.

/tvb

----- Original Message ----- 
From: "Bob Camp" <lists at rtty.us>
To: "'Discussion of precise time and frequency measurement'" <time-nuts at febo.com>
Sent: Friday, February 22, 2013 5:34 AM
Subject: Re: [time-nuts] Logging the grid frequency....


Hi

Don't have a Picotest, but do have similar counters. It's very common for
them to do what looks like a divide of the input frequency before they
measure it. The net result is that you can't measure 60 Hz in 1/60th of a
second. You measure it in 4/60th's of a second instead.

The next problem you will run into is that the counter takes time to arm.
Even if it did the measure in 1/60th of a second, you would only get every
other cycle. 

One way to get every cycle is to measure time rather than frequency. You
time tag every positive zero crossing and then do the math to get frequency.
If you drive one input with a fixed 60 Hz square wave and put the line into
the other input you can get the time offset between them.  

Another approach is to use two conventional period counters and let them
each measure a cycle. One measures while the other is dumping data and
re-arming. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Daniel Mendes
Sent: Friday, February 22, 2013 7:47 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Logging the grid frequency....


Hi, I have a Picotest U6200A. I´m trying to log the grid frequency 
(60Hz) to generate data for my work. I need to get data from every 
cycle. I setup their program (it always starts in chinese... very funny) 
but seems that it can only log every 100ms. Questions:

1) Is that a limitation of the equipment or the software?

2) Using direct comands, can I get data faster?

Thanks for any help...

Daniel





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