Hello: Thanks TVB and Magnus's comment, I think I should ignore that last digit value, it's useless in result. Yes the oscillator in my test is very poor, beacuse it's a OCXO warm-up procedure, the counter's output digit was not regular, I don't know when it add or reduce the digit, but I found in a stablility frequency very close 10Mhz, it not happened. So I powered on a OCXO and observe the output digit in a large range of frequency change.
Hui Zhang At 2013-09-01 01:49:49,"Tom Van Baak" <[email protected]> wrote: >Hi Hui Zhang, > >Yes, I agree it looks strange, but this is normal and correct for the 53132; >or modern frequency counters like it. When it drops a decimal place on the >right it is doing you a favor because that last digit is known to be noise >rather than a real digit of measurement. HP/Agilent has always been concerned >with accuracy and truth. > >In frequency mode, these counters use oversampling algorithms to report the >*best fit* frequency. It works well until the frequency gets very, very close >an exact fractional/multiple of 10 MHz. Then the algorithms no longer improve >phase resolution and the instrument becomes more like a conventional 10 or 11 >digit/second frequency counter. The output is still accurate, but the >precision is reduced accordingly. Again, this is normal. If you've ever >designed a high-resolution frequency counter you understand why. > >Amazingly (and to their credit), the 53132 counter firmware detects this >sub-standard condition and removes digits from the output. It does this >because those digits are recognized to be meaningless. You will also notice in >statistics mode it replaces low order digit(s) with a '*' character. Some >engineer at HP did a lot of work to make sure the instrument did not report >more resolution than was valid. > >There is a footnote in the 53131/53132 manual that explains this: >http://leapsecond.com/pages/53132/53132-reduced-resolution.gif > >In your case, your oscillator is quite poor. Your oscillator varies by >hundreds of microHertz each measurement. The ADEV is about 1e-10. In this >case, it is not a counter problem; it is instability in your oscillator (or >reference). The good news is that for this type of oscillator, your 53132 >counter performs well and you do not need a more expensive time/frequency >comparison instrument. > >If you need more information, let me know. > >/tvb > >----- Original Message ----- >From: "Hui Zhang" <[email protected]> >To: "Discussion of precise time and frequency measurement" <[email protected]> >Sent: Saturday, August 31, 2013 8:06 AM >Subject: [time-nuts] HP53132A's LSD question > > >> Dear group: >> >> I found a strange thing about HP53132A’s output digit, I know the HP53132A >> is a universal counter that have 12 digits per second performance by read >> the manual. By use 10s gate time, I thought it will be 13 digits resolution. >> But I found it can output more digits reads by use GPIB or RS-232 way to >> collect datas. (This is simple way rather than use offset method). I use >> RS-232 cable to connected to my counter to observe the frequency of a OCXO, >> I got these output result ( a part of long sequence): >> >> 9.999,967,286,098,0 MHz >> 9.999,981,814,726,9 MHz >> 9.999,991,573,702,0 MHz >> 9.999,997,482,253,0 MHz >> 9.999,999,945,685 MHz >> 10.000,000,472,030,4 MHz >> 10.000,000,460,991,3 MHz >> 10.000,000,352,570,9 MHz >> 10.000,000,254,108 MHz >> 10.000,000,183,759 MHz >> 10.000,000,136,842 MHz >> .. >> . (Omitted few lines) >> . >> 10.000,000,039,724 MHz >> 10.000,000,006,299 MHz >> 9.999,999,992,692 MHz >> 9.999,999,990,674 MHz >> 9.999,999,989,094 MHz >> 9.999,999,995,662 MHz >> 9.999,999,993,829 MHz >> >> The question is in first four lines the reads is 14 digits, but in line 5, >> the digits reduce to 13 digits, and then, it’s became 15 digits in line >> 6(because over 10Mhz). After 3 lines, the reads reduce one digits again to >> became 14 digits(also over 10Mhz), again after that few lines the frequency >> less that 10Mhz, it return to 13 digits like last few line. My question is >> what determines the HP53132A’s resolution? Why the output is variable digits >> even the had very close frequency? Any comment will be appreciate. >> >> >> >> Hui Zhang > > >_______________________________________________ >time-nuts mailing list -- [email protected] >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
