IMHO these systems are not really worth the expense. Infact systems
based on pH can be misleading as the solutions are buffered, this means
they will tend to keep a constant pH right up to the moment they fail,
irrespective of the amount of active chemical in the system.
You need something which measures the actual amount of chemical in the
system and so far as I know this has to be titrated off line. I think
you would be better off initially setting up some off line titrations to
get some idea of the make up/usage. Using this you can then set a
reasonably relevant work order for top up and for setting the period for
routine change. This makes an easily manageable system and although it
could be argued that you would be changing material unnecessarily the
actual incremental cost of this is slight compared to the cost of
continual monitoring.
After the initial period occasionally doing a titration as a check or if
works loads change. The only continuous in line monitoring that I would
suggest would be on conductivity of [exiting] final rinse water. You can
also set an upper limit on this to shut down if something goes
completely wrong up stream.

Regards

Mike Fenner

Indium Corporation
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tom Gervascio
Sent: Thursday, November 20, 2003 12:22 PM
To: [log in to unmask]
Subject: [TN] Automatic monitoring systems for in line cleaners


We are considering using an automatic system to monitor and control
additions of a saponifier to our Electrovert H400+ wash. Any
recommendations on systems that other's have used? Any trade-offs on
closed loop monitoring systems using pH versus refractometer? I thought
that if you use water soluble masks that the dissolved materials might
influence the dissolved solids measured with refractometer. However it
seems that drag out with normal operation approaches 7 gal/8 hour shift.
with a prewash and wash capacity of 95 gallons this means that over 12
shifts that the wash should be turned over but I suspect that all the
material may not be turned over due to dead spots in the construction of
the wash (i.e. 2" level in wash below a U joint that connects the
prewash to the wash section). That said is location of the sensors
critical- i.e. place them in these areas where the wash may be stagnant
or items may settle to the bottom of tanks and heaters.

Thanks for the input

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