pH controller sensitivity

From: Doug Valverde <75051.160 at compuserve_com>
Date: 07 Oct 95 08:43:49 EDT

> Do have a question though for those of you with pH controllers.  How
> precisely is the pH controlled by these?  I have seen some with +-
> 0.02 but am unsure just how precisely I should control the pH of a
> tank.  Is 0.1 enough or should I use finer settings?  I can control it
> up to the precision of the probe itself, but just do not know if I
> need to or if I can use a wider range of control.

The Sandpoint controllers have setpoints at +/- 0.05 around the
desired pH.  The swing of 0.1 seems to work fine and doesn't exhibit
too much solenoid clicking.

The Dupla controllers are supposedly able to "learn" the
characteristics of your system and can compensate for any lag and
overshoot asociated with your reactor, i.e., it will turn on the CO2 a
but before the upper setpoint is reached and turn it off just before
the lower setpoint is reached to avoid over- and under-shoot.  I'm not
sure how tightly they control the pH, but I would guess they try to
keep it very constant.  We have never had a problem with over/under
shoot so I wonder if the extra $$$ is worth it.