[time-nuts] Stanford Research SR620 Measurement Bias

Stan swperk at earthlink.net
Thu Oct 1 16:22:14 UTC 2009


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.koegel5 at gmail.com>
Subject: Re: [time-nuts] Stanford Research SR620 Measurement Bias
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Message-ID:
	<390229150909300705v1808d748h5376cf05e7ae637a at 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
(9'999'999.9997x....10'000'000,0003)
previous value   -210 counts
with the internal reference  +/- 6 counts
previous value   -25 counts

Best regards

J?rg K?gel





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