Re: CO2 regulators

[George Booth <booth at lvld_agilent.com>]

> Date: Sat, 9 Sep 2000 03:09:42 -0400
> From: Ellen & William Beckerman <e_mail at bellsouth_net>
> 
> Anyone else out there with anything info good, bad or indifferent on 
> CO2/pH controllers???

I have an older '98 Pet Warehouse catalog at work and it lists a couple of pH 
controllers. One in particular appears to be marketed by American Marine and is 
a "Pinpoint pH Controller".  This unit looks *exactly* like the original pH 
controller sold by Sandpoint. IMHO, this unit is very poor, unless the design 
has been updated.   

The biggest problem we saw with it was it would oscillate between on and off at 
it's tightest setting. You can adjust both the set point (i.e., "7.0") and the 
hysteresis (i.e., "+/- 0.2"). If you chose the tightest hysteresis, you would 
often wake up to a buzzing noise as it hunted for the right state. My analysis 
was poor power supply bypassing. When the controller actuated the CO2 solenoid, 
the circuit supply voltage jumped, altering the pH value read. The unit would 
then see the pH being above the set point and would turn the solenoid off. Then 
it would see the pH being below the set point. Repeat until whacked upside the 
head by owner.  

Another shortcoming was the ergonomics. It had knobs for doing the calibration. 
It had recessed slotted screws for the set point and hysteresis. It was very 
easy to bump the knobs and knock it out of calibration. Why on Earth did they 
use knobs for cal? 


George Booth in Ft. Collins, Colorado (booth at frii_com)
  http://www.frii.com/~booth/AquaticConcepts

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