Chemtrac Systems, Inc.
Page 44
less than 50% of what the new probe reads and/or noticeably less stable, it is
recommended to replace the old set unless the operator feels confident that the
old set was performing satisfactorily. Once the signal strength from a probe and
piston set has degraded down to 50% to 25% of what a new set’s signal strength
is, the parts should be considered worn and probably in need of replacing.
It may not be necessary to replace both the piston and the probe at the same
time as usually the piston wears faster than the probe. To check this, simply
install a new piston with the old probe and compare those readings to the ones
obtained with the new piston and new probe combination. If the old probe and
new piston combination produce a reading that is within 50% or more of the new
set, then the probe can still be used as long as the new piston is installed. The
same procedure should be followed with a new probe and old piston to
determine if the old piston is still suitable for use. Using this procedure, the
operator can determine which part, if not both, needs to be replaced. Be sure to
order a replacement part(s) to have on hand as a spare once you have installed
the new probe and/or piston to replace the worn part(s).
Simple Functionality Test
The procedure of pouring raw water into the probe block to check the probes for
wear can also be used to check the probe’s response and/or troubleshoot the
system. Many times when there is a problem associated with the monitor, the
operator will assume the instrument is at fault. If the operator does not have an
easy method of testing the monitor’s functionality, he will most likely not look for
another cause. A simple method of checking the monitor’s performance is to
pour untreated, raw water into the probe as outlined above. First, verify that the
raw water reading is significantly different from the treated water reading. The
raw water reading should be more negative than the treated water sample by at
least 50 units (taking into consideration that the gain has been properly set and
that coagulant dosage is greater than a few ppm). The raw water reading will
also normally be greater than –100 on 1X gain (except with samples that have a
high alkalinity/conductivity). The reading on the raw water should also be stable
and not erratic or oscillating. Finally, add a small amount of coagulant to the raw
water sample and pour the sample into the sensor to verify the reading responds
by moving in the positive direction. If the unit responds as outlined above, the
unit is most likely performing within specifications. If you are unsure about your
results, or cannot find another cause for whatever problems you are having with
the monitor (e.g. lack of response, erratic reading), then contact the factory.
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