I guess it's semantics. If an undesired output event causes a corrective action
to be taken in a previous stage isn't this a closed loop? I believe it is, even
if it's a "man-in-the-loop" system, i.e. I see on the oscilloscope that I'm flat
topping so I turn the audio gain down to correct it.
On 2/12/2015 9:59 PM, Don Wilhelm wrote:
Wes,
An analog open loop ALC is one in which the drive is reduced in response to an
overload condition (high SWR, power level that exceeds the maximum set
level). The response is applied only after the offending condition occurs -
that is an open loop system.
With the K3, KX3 and K2 power control system being a closed loop system, that
condition does not exist. The overshoot possibility is detected early and the
power is reduced accordingly without PA overshoot and the PA going into a
distortion region.
If you have any understanding about closed loop control systems, you will then
understand 'damping' conditions. Underdamped systems will oscillate near the
'set point' while overdamped systems will never come up to the set point.
Critically damped systems will quickly settle to the set point and maintain
the proper condition (power level, temperature, you 'name it' condition). In
the case in point, the power level is the 'set point' that is considered. An
open loop system is totally undamped and will only respond 'after the fact' to
conditions that exceed certain thresholds. Closed loop systems approach those
thresholds with actions that will result in critical damping of the response
mechanism.
73,
Don W3FPR
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