[time-nuts] Parallel voltage regulators

Bill Hawkins bill at iaxs.net
Fri Oct 26 20:06:33 EDT 2007


Well, there is another trick of the control trade, used to bring
batch process reactors up to the desired temperature in a hurry.

At first, you turn on full heat for an experimentally determined
time. You turn it off at the end of that time, before the oven has
reached final temperature. You leave it off for an experimentally
determined time while the oven coasts up to the peak temperature.

If you've done it right, the peak temperature is the oven setpoint.

Then you preset the oven controller to its normal output. This is
the value that you read when the output is settled out from a plain
old startup.

Now the controller is at its setpoint, and the output is at its
operating point. Turn on the oven supply regulator and enjoy 
relatively stable control. This method is considerably faster
than letting the controller respond to the turn on transient by
oscillating its way into steady state.

Bill Hawkins
 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Max Robinson
Sent: Friday, October 26, 2007 4:08 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Parallel voltage regulators

); SAEximRunCond expanded to false
Errors-To: time-nuts-bounces+bill=iaxs.net at febo.com RETRY

I do have some experience with temperature controlled ovens.  I found
that a long term plot of the temperature while using an unregulated
supply on the oven heater showed small random variations due to voltage
variations.  When the oven heater was put on a regulated supply the line
became flat.  The problem here seems to be during the heat up cycle.
The voltage doesn't need to be regulated during that time.  You might
try sensing the error signal and when it is outside of the linear
control range you could switch in a parallel transistor and resistor to
handle the warm-up current and it would switch out when the oven has
stabilized at the lower current.

Regards.

Max.  K 4 O D S.

Email: max at maxsmusicplace.com

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----- Original Message -----
From: "Bill Hawkins" <bill at iaxs.net>
To: "'Discussion of precise time and frequency measurement'" 
<time-nuts at febo.com>
Sent: Friday, October 26, 2007 1:21 AM
Subject: Re: [time-nuts] Parallel voltage regulators


> There is a concept in temperature control called feed-forward.
>
> In this case you would sample the supply line with an inverting
> amplifier and use it to increase the oven drive signal as the
> line voltage decreases. The goal is to keep the integral term
> from changing as the line voltage changes. It is not as easy
> as it sounds.
>
> Bill Hawkins
>
>
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