[MyHosting.com]   [KO4BB Home Page]   [Manuals Home Page]   [KO4BB Wiki]
 

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

precision_timing:lpro_disciplining_with_thunderbolt [2013/01/08 19:00]
precision_timing:lpro_disciplining_with_thunderbolt [2013/01/08 19:00] (current)
Line 1: Line 1:
 +===== LPRO disciplining with Thunderbolt =====
 +
 +// From the [[Time Nuts Mailing List]]:
 +//
 +
 +In response to request on how I set up my Tbolt with a long time constant to directly discipline a LPRO 101 Rubidium;
 +
 +I use a standard LPRO 101 Rb as an external replacement for the Tbolt'​s internal OCXO,
 +and connect the LPRO's external C_Field adjustment input to the Tbolt'​s Dac out thru a 1K ohm resistor (added as protection for the Tbolt.)
 +
 +Due to Tbolt'​s software limitations,​ an Extended_TC setting method needs to be used for setting Time Constants above 1000 sec.
 +
 +To calculate the Tbolt'​s Effective TC setting using this extended TC setting method:
 +
 +  - The Effective_TC of the TBolt is Actual_TC setting times the Multiplier_Factor
 +  - The Effective_Damping factor of a Tbolt is Actual_Damping setting divided by the square root of the Multiplier_Factor
 +  - The Multiplier_Factor is equal to "​Dac_Gain used / Actual_EFC_Gain"​
 +
 +
 +**Example for setting Tbolt'​s Effective_TC = 20,000 sec, Effective_Damping factor = 0.6 for a LPRO.**
 +
 +  - Use Multiplier_Factor = 100
 +  - Dac Gain = +0.90 Hz/V
 +  - TC = 200 sec
 +  - Damping = 6.0
 +  - Set Initial Dac value to +2.5V,
 +
 +After adjusting ​ the LPRO's to 10 MHz using it's internal freq C field pot (with the external C_Field input floating ​ at 2.5V), it is a good idea to limit the Tbolt'​s Dac output swing by setting the Max_Dac out to + 3.0 V, and the Min_Dac out to + 2.0 V.
 + 
 +
 +**Example of setting Tbolt'​s Effective_TC = 5,000 sec,  Effective_Damping factor = 0.7**   
 +
 +(I use this setting to discipline a very stable external dual oven HP 10811.)
 +
 +  - Use Multiplier factor = 10
 +  - Dac Gain = -3.24 Hz/V    (Actual Gain for this 10811 is -0.324 Hz/V)
 +  - TC = 500 sec
 +  - Damping = 2.2
 +
 +The effective TC can be measured by how long of time that it takes for a Freq offset error to return to zero, best measured by using LH's Dac voltage plot.
 +
 +The effective Damping can be calculated by how much Freq error overshoots there is, which in turn determines how long of time the Phase error takes to return to zero.
 +
 +For a damping =  0.6  the Freq overshoot is 33% and Phase correction time is about 3.5 times the Freq correction time  (10%  phase overshoot)
 +
 +Using a damping of  0.7,  the Freq overshoot is 25%, & phase correction time is  5x the TC setting. (no phase overshoot)
 +
 +With a damping factor of 1.0, there will be very little Freq overshoot, but that causes the phase correction time to be very long. (overdamped Phase response)
 +
 +Using Lady Heather, the effective TC and Damping_Factor settings can be verified by plotting the offset freq recovery time to an intentional Dac step error:
 +
 +  - Disable the control loop (D D)
 +  - Change the Dac voltage (D S ... ) by an amount equal to 1e-10 or 1e-9 (verify on Osc plot)
 +  - Enable the control loop (D E)
 +  - Plot the Phase, Dac_Voltage and Osc_Freq over at least 5 times the effective TC setting.
 +
 +Before replacing a Tbolt'​s internal Osc with a cheap rubidium, one should understand the noise tradeoffs, especially at low taus.
 +Lots of plots available on request
 +
 +ws
  
 
precision_timing/lpro_disciplining_with_thunderbolt.txt ยท Last modified: 2013/01/08 19:00 (external edit)
 
Recent changes RSS feed Creative Commons License Donate Powered by PHP Valid XHTML 1.0 Valid CSS Driven by DokuWiki
Except as noted, this entire site Copyright © 2002-2017. KO4BB All rights reserved.