[time-nuts] Fury - Rubidium - PIS

Brian Kirby kilodelta4foxmike at gmail.com
Tue Jul 27 21:51:27 EDT 2010

That part I understand (your drawing), its a basic phase lock loop. 
What I am having trouble with is the Fury's commands relationship.

The Fury controller has the following SERVO commands to set up the loop:

SERVo:DACG which is the DAC gain, a control voltage range ?
range is 0.1 to 10,000 -- the DAC is 0 to +5V

SERVo:EFCS which is the EFC Scale, proportional gain of the PID loop
range is 0.0 to 500.0 -- 0.7 example for a good double oven and 6.0 for 
a simple single oven

SERVo:EFCD which is IIR filter time constant
range is 0.0 to 4000.0 -- example between 10 and 50

Thanks - Brian KD4FM

On 7/27/2010 8:36 PM, J. Forster wrote:
>> I read the article on PID on Wikipedia last night.  I do not fully
>> understand it, but I see/learning some of the relationship.
> Here's a very quick primer:
> Consider a very simple control position servo loop:
> Pos. Input --- + (SUM)--- PID --- AMP>  --- MOTOR ===== Output Pos
>                     |-                               ||
>                     |                               POS Sensor
>                     |                                 |
>                     -----------------------------------
> If you put an upwards step into the Pos Input the output of the SUM goes
> up. This is applied to the AMP via the PID network and the MOTOR stasrts
> up, turning the output shaft. As the Output shaft turns, the position
> sensor output rises. That subtracts from the commanded position in the
> SUM, reducing the AMP input.
> Thats how the P = Proportional signal drives the loop to null.
> However, in order for the motor to turn some non-zero voltage needs to be
> applied. As the SUM output approaches zero the motor drive ceases and the
> loop never reaches null. So the I = Integral term is added. If the loop
> stops just shy of null, the SUM output will not be zero. The I Integrator
> takes the near-null voltage and integrates it (Vsum dT) which will
> eventually rise sufficiently to drive the motor to null.
> However, the motor does not stop instantly when the SUM reaches zero
> because of inertia, so it overshoots. So the D = Derivative term
> (dVsum/dT)is added in to cut the motor drive as the loop approaches null.
> Note, in general the I term is destabilizing and the D term is
> stabilizing, as long as you are considering frequencies below where the
> othy components have significant phase shift.
> -John
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