# [time-nuts] (no subject)

Bob Camp kb8tq at n1k.org
Sat Jan 24 21:05:38 EST 2015

```Hi

A classic control loop in it’s simplest form has only one term. That is often referred to as a proportional term. When the control signal (or error) changes by A the output changes by A times that term. Often in shorthand notation this term is refereed to as a P term.

The next thing that some people add to a control loop is an integrator. It looks at the control signal (or error) has a constant offset of A, the integrator sums up the A’s. The output of an integrator would eventually go to infinity with a constant control input (or error) into it. This term is often referred to as an I term.

Lastly people add a term to the control loop that responds to the rate of change in the control signal (or error). The faster the change, the bigger this signal gets. This is commonly refereed to as a Derivative term. In shorthand it’s talked about as the D term.

The net result is a three element control loop running what’s called a PID algorithm .

The P and I can also be described by a time constant and a damping. That’s what the Trimble software lets you do. The implication is that it’s just a PI loop. In fact it appears to be a PID loop and you can’t get at the D term.

For a much more clearly worded explanation of all this, there’s

http://en.wikipedia.org/wiki/PID_controller

Bob

> On Jan 24, 2015, at 6:35 PM, Cash Olsen <radio.kd5ssj at gmail.com> wrote:
>
> Bob,
>
> I am relatively new to the list and still learning the jargon and
> concepts. You wrote: "There does appear to be a D in the TBolt loop.
> For what ever reason, that’s not a changeable value. The D does scale
> with the time constant."
>
> Could you or one of the other members elaborate on the what is meant
> by "D" above. Does it have anything to do with a flat spot in the
> loop?
>
> --
> S. Cash Olsen KD5SSJ
> ARRL Technical Specialist
>
> Message: 10
> Date: Sat, 24 Jan 2015 09:18:15 -0500
> From: Bob Camp <kb8tq at n1k.org>
> To: Discussion of precise time and frequency measurement
>        <time-nuts at febo.com>
> Subject: Re: [time-nuts] Questions regarding tuning Thunderbolt with
> Message-ID: <6581EB02-9792-432F-B143-25B41FB290DB at n1k.org>
> Content-Type: text/plain; charset=utf-8
>
>
> There does appear to be a D in the TBolt loop. For what ever reason,
> that’s not a changeable value. The D does scale with the time
> constant.
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```