Re: [time-nuts] Stanford Research SR620 Measurement Bias
One last follow-on to this thread: In order to speed up the calibration process by being able to see the measurement results in real time while adjusting the two CalByte values, I connected the SR620 scope outputs and monitored the graphical output on my oscilloscope. It turns out that the graphical output still works while adjusting the CalBytes and makes the setup simpler (for me, anyway) than using a terminal emulator on the SR620 serial port to make the adjustments. Stan Message: 1 Date: Wed, 30 Sep 2009 16:05:46 +0200 From: J?rg K?gel j.koeg...@gmail.com Subject: Re: [time-nuts] Stanford Research SR620 Measurement Bias To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: 390229150909300705v1808d748h5376cf05e7ae6...@mail.gmail.com Content-Type: text/plain; charset=ISO-8859-1 Make the adjustment in the correct sequence: 1. Set the Cal jumper to Cal Enable 2. Connect the reference to Ext Ref (rear) and Input A 3. Switch the counter to Ext Ref 4. Set the CalByte 50 for the best display (this is a very fine adjustement) 5. Switch the counter to Int Ref 6. Set the CalByte 4 for the best display (this adjustement is coarse, optimize!) 7. Set the Cal jumper to Cal Disable After this calibration my SR620 is with the external reference +/- 3 counts (9'999'999.9997x10'000'000,0003) previous value -210 counts with the internal reference +/- 6 counts previous value -25 counts Best regards J?rg K?gel ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Thanks for the tip! Your method eliminates the interaction between the effects of the CalByte 50 and CalByte 4 adjustments in a way that makes perfect sense. After some trial and error, I found that it's easier to get the CalByte 50 adjustment right using the short (0.01 s) timebase setting rather than the long (1 s). My SR620 is now a whole lot more accurate and the bias is essentially gone. My one complaint is that I can't see the actual counter readings while I'm adjusting the CalByte values. I haven't looked into this yet, but are the readings being outputted from the scope or printer outputs on the rear panel during the cal adjustments? Stan Message: 1 Date: Wed, 30 Sep 2009 16:05:46 +0200 From: J?rg K?gel j.koeg...@gmail.com Subject: Re: [time-nuts] Stanford Research SR620 Measurement Bias To: Discussion of precise time and frequency measurement time-nuts@febo.com Message-ID: 390229150909300705v1808d748h5376cf05e7ae6...@mail.gmail.com Content-Type: text/plain; charset=ISO-8859-1 Make the adjustment in the correct sequence: 1. Set the Cal jumper to Cal Enable 2. Connect the reference to Ext Ref (rear) and Input A 3. Switch the counter to Ext Ref 4. Set the CalByte 50 for the best display (this is a very fine adjustement) 5. Switch the counter to Int Ref 6. Set the CalByte 4 for the best display (this adjustement is coarse, optimize!) 7. Set the Cal jumper to Cal Disable After this calibration my SR620 is with the external reference +/- 3 counts (9'999'999.9997x10'000'000,0003) previous value -210 counts with the internal reference +/- 6 counts previous value -25 counts Best regards J?rg K?gel ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Stan, Stan wrote: Thanks for the tip! Your method eliminates the interaction between the effects of the CalByte 50 and CalByte 4 adjustments in a way that makes perfect sense. After some trial and error, I found that it's easier to get the CalByte 50 adjustment right using the short (0.01 s) timebase setting rather than the long (1 s). My SR620 is now a whole lot more accurate and the bias is essentially gone. Wonderfull! My one complaint is that I can't see the actual counter readings while I'm adjusting the CalByte values. I haven't looked into this yet, but are the readings being outputted from the scope or printer outputs on the rear panel during the cal adjustments? Use the serial port. You can adjust the calibration values using the BYTE and WORD commands. See page 40. read word 50: WORD?50 write word 50 to 1234: WORD50,1234 That way you can keep the reading on the display while using a terminal emulator to adjust it. It should not be too hard to make a little program to automize this calibration. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Make the adjustment in the correct sequence: 1. Set the Cal jumper to Cal Enable 2. Connect the reference to Ext Ref (rear) and Input A 3. Switch the counter to Ext Ref 4. Set the CalByte 50 for the best display (this is a very fine adjustement) 5. Switch the counter to Int Ref 6. Set the CalByte 4 for the best display (this adjustement is coarse, optimize!) 7. Set the Cal jumper to Cal Disable After this calibration my SR620 is with the external reference +/- 3 counts (9'999'999.9997x10'000'000,0003) previous value -210 counts with the internal reference +/- 6 counts previous value -25 counts Best regards Jürg Kögel 2009/9/28 Magnus Danielson mag...@rubidium.dyndns.org: Ulrich, Ulrich Bangert wrote: Stan, I believe I made it with calbyte 4 as described on page 71 of the manual. How does that explains the shift with time-base? I think it is the wrong way around for a time-bias like this. Tweaking the time-base will maybe fix it for one of the time-bases, but not for the others. I'm digging deeper into this, I want to know how to fix it if I see it on mine. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Hi Jürg, Jürg Kögel wrote: Make the adjustment in the correct sequence: 1. Set the Cal jumper to Cal Enable 2. Connect the reference to Ext Ref (rear) and Input A 3. Switch the counter to Ext Ref 4. Set the CalByte 50 for the best display (this is a very fine adjustement) 5. Switch the counter to Int Ref 6. Set the CalByte 4 for the best display (this adjustement is coarse, optimize!) 7. Set the Cal jumper to Cal Disable After this calibration my SR620 is with the external reference +/- 3 counts (9'999'999.9997x10'000'000,0003) previous value -210 counts with the internal reference +/- 6 counts previous value -25 counts Thanks for that clarification. It seems very reasnoble. I obviously never bothered to do a carefull calibration of my SR620, so I haven't picked up the fine grain details involved with these procedures. This is a good reminder that I should pay attention to those details. I think I can say the same for most of my gear. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Stan, I own a SR620 as well and mine behaves the same (while with a different number of counts) so your's is surely not defective! My understanding a few years ago when I acquired the counter was that this bias is not due to a adjustment in the normal sense but to set a parameter in the counter's eeprom to a correct value. Since this parameter is limited to a certain precisison you can make some effort in minimizing this bias but you should not expect to make it exactly zero. The manual explains how to do but you do not find the procedure where you would have expected it. Best regards Ulrich Bangert -Ursprungliche Nachricht- Von: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] Im Auftrag von Stan Gesendet: Sonntag, 27. September 2009 18:15 An: time-nuts@febo.com Betreff: [time-nuts] Stanford Research SR620 Measurement Bias I just acquired an SR620 that looks to be in excellent condition. I've noticed something in its operation and I'm not sure if it represents a problem, a calibration issue, or if it's just a feature. Yesterday, after letting the counter warm up for an hour, I calibrated the 10 MHz timebase and did a couple of Auto-Cals (just to be sure), but even after all of that, there's still a bias of somewhere between 40 and 70 counts in the frequency readout, independent of the gate time. For example, if I measure the 5 MHz output of my 5065A, and using a sample size of 1, here's what I see (these are representative readings-the values are bouncing up and down by 10 or 20 counts and I'm visually averaging them). Increasing the sample size has no effect other than to reduce the variability of the measurements, but the bias is still the same magnitude: 1 sec Gate: 5,000,000.00054 Hz 0.1 sec Gate: 5,000,000.0060 Hz 0.01 sec Gate: 5,000,000.055 Hz 1 Period Gate: 5,004,7__ Hz I've had several HP 5370A/B counters, but never one of these. As I recall-and it's been a while-there's an adjustment in the 5370A/B for the interpolators that can remove this sort of bias. Is there a similar adjustment in the SR620? I've been through the manual and don't see anything obvious. Thanks for any advice! Stan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Hi Ulrich, Thanks for the insight! I tried manually adjusting the value of CalByte 50 (as per Magnus' suggestion), but it did not make the problem go away. There is interaction between this adjustment and the CalByte 4 adjustment for timebase accuracy, and when all was said and done, I didn't notice any significant difference in the offset. Where in the manual does it describe the procedure to minimize the bias? It's definitely not where I would have expected it to be! Regards, Stan Message: 1 Date: Mon, 28 Sep 2009 09:08:21 +0200 From: Ulrich Bangert df...@ulrich-bangert.de Subject: Re: [time-nuts] Stanford Research SR620 Measurement Bias To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Message-ID: a4d0a2a6239b4798ab28e7193a646...@athlon Content-Type: text/plain; charset=us-ascii Stan, I own a SR620 as well and mine behaves the same (while with a different number of counts) so your's is surely not defective! My understanding a few years ago when I acquired the counter was that this bias is not due to a adjustment in the normal sense but to set a parameter in the counter's eeprom to a correct value. Since this parameter is limited to a certain precisison you can make some effort in minimizing this bias but you should not expect to make it exactly zero. The manual explains how to do but you do not find the procedure where you would have expected it. Best regards Ulrich Bangert ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Stan, I believe I made it with calbyte 4 as described on page 71 of the manual. Best regards Ulrich -Ursprungliche Nachricht- Von: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] Im Auftrag von Stan Gesendet: Montag, 28. September 2009 14:46 An: time-nuts@febo.com Betreff: Re: [time-nuts] Stanford Research SR620 Measurement Bias Hi Ulrich, Thanks for the insight! I tried manually adjusting the value of CalByte 50 (as per Magnus' suggestion), but it did not make the problem go away. There is interaction between this adjustment and the CalByte 4 adjustment for timebase accuracy, and when all was said and done, I didn't notice any significant difference in the offset. Where in the manual does it describe the procedure to minimize the bias? It's definitely not where I would have expected it to be! Regards, Stan Message: 1 Date: Mon, 28 Sep 2009 09:08:21 +0200 From: Ulrich Bangert df...@ulrich-bangert.de Subject: Re: [time-nuts] Stanford Research SR620 Measurement Bias To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Message-ID: a4d0a2a6239b4798ab28e7193a646...@athlon Content-Type: text/plain; charset=us-ascii Stan, I own a SR620 as well and mine behaves the same (while with a different number of counts) so your's is surely not defective! My understanding a few years ago when I acquired the counter was that this bias is not due to a adjustment in the normal sense but to set a parameter in the counter's eeprom to a correct value. Since this parameter is limited to a certain precisison you can make some effort in minimizing this bias but you should not expect to make it exactly zero. The manual explains how to do but you do not find the procedure where you would have expected it. Best regards Ulrich Bangert ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Ulrich, Ulrich Bangert wrote: Stan, I believe I made it with calbyte 4 as described on page 71 of the manual. How does that explains the shift with time-base? I think it is the wrong way around for a time-bias like this. Tweaking the time-base will maybe fix it for one of the time-bases, but not for the others. I'm digging deeper into this, I want to know how to fix it if I see it on mine. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Stanford Research SR620 Measurement Bias
I just acquired an SR620 that looks to be in excellent condition. I've noticed something in its operation and I'm not sure if it represents a problem, a calibration issue, or if it's just a feature. Yesterday, after letting the counter warm up for an hour, I calibrated the 10 MHz timebase and did a couple of Auto-Cals (just to be sure), but even after all of that, there's still a bias of somewhere between 40 and 70 counts in the frequency readout, independent of the gate time. For example, if I measure the 5 MHz output of my 5065A, and using a sample size of 1, here's what I see (these are representative readings-the values are bouncing up and down by 10 or 20 counts and I'm visually averaging them). Increasing the sample size has no effect other than to reduce the variability of the measurements, but the bias is still the same magnitude: 1 sec Gate: 5,000,000.00054 Hz 0.1 sec Gate: 5,000,000.0060 Hz 0.01 sec Gate: 5,000,000.055 Hz 1 Period Gate: 5,004,7__ Hz I've had several HP 5370A/B counters, but never one of these. As I recall-and it's been a while-there's an adjustment in the 5370A/B for the interpolators that can remove this sort of bias. Is there a similar adjustment in the SR620? I've been through the manual and don't see anything obvious. Thanks for any advice! Stan ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Stanford Research SR620 Measurement Bias
Stan. Calibrating the units timebase per page 76 of the manual you can manually adjust the calbyte 4 word until the counter averages zero offset plus minus around the 5Mhz. You will still have the .0060 bias but it will plus and minus 30. Corby Dawson Best Weight Loss Program - Click Here! http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTFoYckJJTSz9ZWtSYYnIdcHHnuViYytOdHmKkw6a10JBXXussDDPq/ ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Corby, Corby Dawson wrote: Stan. Calibrating the units timebase per page 76 of the manual you can manually adjust the calbyte 4 word until the counter averages zero offset plus minus around the 5Mhz. You will still have the .0060 bias but it will plus and minus 30. This will not solve his issue. Notice how the error increases in size by about a decade as the time-base steps down by a decade. This is not a time-base issue, this is a time-delay issue, a static delay between start and stop events. I am preparing a more detailed answer. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Stanford Research SR620 Measurement Bias
Stan, Stan wrote: I just acquired an SR620 that looks to be in excellent condition. I've noticed something in its operation and I'm not sure if it represents a problem, a calibration issue, or if it's just a feature. Yesterday, after letting the counter warm up for an hour, I calibrated the 10 MHz timebase and did a couple of Auto-Cals (just to be sure), but even after all of that, there's still a bias of somewhere between 40 and 70 counts in the frequency readout, independent of the gate time. For example, if I measure the 5 MHz output of my 5065A, and using a sample size of 1, here's what I see (these are representative readings-the values are bouncing up and down by 10 or 20 counts and I'm visually averaging them). Increasing the sample size has no effect other than to reduce the variability of the measurements, but the bias is still the same magnitude: 1 sec Gate: 5,000,000.00054 Hz 0.1 sec Gate: 5,000,000.0060 Hz 0.01 sec Gate: 5,000,000.055 Hz 1 Period Gate: 5,004,7__ Hz Notice how the bias shift up one decade as the time-base shifts down a decade. Consider that this is a reciprocal counter which measures the number of events and amount of time (in its time-base): freq = Events / Time As we step Time a decade down, the error increases by a decade, but an offset in number of Events should produce a much larger error (5 Hz, 50 Hz and 500 Hz respectively) so we must look at the time side of the division. To facilitate this, I make up estimates for the Event counter and Gate Counter and runs the calculation backwards: freq = Events / Time = Events / (GateCount * 90 MHz - Start + Stop) Events = freq * Time Time = Events / freq tauEventsGate Count -Start + Stop 1 s 5.000.000 90.000.000 -107,999 ps 100 ms 500.000 9.000.000 -119,999 ps 10 ms50.000900.000 -109,999 ps 500 ns 1 18 -199,999 ps This is fairly consistent. Notice that the 1 cycle path is different from the internally gated path. However, the cause of this time error needs some more thought. If it where an inconsistens between the start and stop interpolators, the error would shift as the internal time-base beats against the internal 10 MHz oscillator (which is stepped up to the 90 MHz coarse counter clock). However, a voltage error between start and stop trigger voltage would produce a stable offset. Since the start and stop input selection is the same in the SR620 when doing frequency measurments, this flaw is canceled out. The ST620 uses a little dedicated circuit to post-process the frequency measurements and produce the start and stop signals being sent to measurement channel muxes. After this mux signals goes to the event and gate counter setups and also to the interpolator logics. Any systematic time-offset due to propagation delay variations in the start and stop delay of that circuit will introduce a time-bias into frequency measurements. Looking at the overview of calibration bytes, byte 50 looks like the byte of interest. However, it is claimed that byte 50 is among those that is trimmed by AutoCal, which makes the peculiar statement on page 78 that Frequency does not need calibration. It should say it does not need manual calibration. It may be that you could tweak this value and see how it changes your readings. I've had several HP 5370A/B counters, but never one of these. As I recall-and it's been a while-there's an adjustment in the 5370A/B for the interpolators that can remove this sort of bias. Is there a similar adjustment in the SR620? I've been through the manual and don't see anything obvious. It is hidden in the details. I think you with the brief analysis above should be able to come to the same conclusion. Thanks for any advice! Hope I got you onto the track. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
