In-Situ TROLL 9500 Operators Manual - Manual (Page 67)

60 TROLL 9500 Operator’s Manual 0095110 rev. 007 01/09
Q:
A:
What is the difference between NOMINAL and STABLE?
To meet the criteria for a valid calibration point, the change
(deviation) in sensor response is monitored over time. The
software is looking for the calibration solution temperature
and the sensor readings to settle over a specific time period.
The criteria for STABLE are designed to meet the published
specifications. The NOMINAL criteria are designed to
shorten the calibration time when an approximate calibration
is acceptable. When the deviation falls within the limits of
the “loosened” specifications, NOMINAL is displayed in the
Status area, and the Accept button becomes available to
store the current calibration point.
Accepting a NOMINAL value may save considerable time.
In some cases, especially if the sensors have been soaking
in the solution for several minutes prior to calibration, the
accuracy achieved by accepting a nominal value may be
very similar to that obtained by waiting for complete stability.
sensor
removal
tool
REMOVING SENSORS
Sensors may be removed for inspection, cleaning, routine mainte-
nance, and storage. Because the smart sensors retain calibration
information, they may be removed and re-installed—even in another
MP TROLL 9500— as often as necessary.
Remove a sensor by positioning the yoke of the sensor
removal tool at the point where the sensor enters the
sensor block. Firmly pry the sensor upward until it pops
out.
Sensor O-Rings
Two Viton® o-rings on each sensor provide a watertight seal against
water leakage into the instrument body. We recommend that you
inspect these o-rings each time you remove or install a sensor. Check
carefully for cracks, tears, splitting, shredding, and other damage. If
the o-rings are in good condition, apply silicone lubricant before in-
stalling the sensor again. Remove excess lubricant with a tissue, and
take care to keep grease away from the area around the connector at
the bottom of the sensor. Should lubricant get into this area, it can be
removed with a clean cotton swab.
If the o-rings become damaged to the extent that no longer provide an
effective seal, they should be replaced. Sensor o-rings and lubricant
are available from In-Situ Inc. or your distributor.
CALIBRATION OVERVIEW
The MP TROLL 9500 and its control software provide several options
for calibration of the water-quality sensors. Select the method that
suits the time you have at your disposal and the degree of accuracy
you want to achieve when measuring water-quality parameters.
Satisfactory results may be achieved using the Quick Cal procedure.
Some sensors can even return nominal results straight out of the box
using the factory-supplied default calibration coefficients. However,
for best results we recommend a full traditional calibration procedure
before the first field use, and periodic checks and recalibrations as
necessary thereafter.
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TRADITIONAL CALIBRATION
A full traditional calibration, guided by software wizards, can achieve
the highest level of accuracy. Some sensors require a single-point
calibration, others present a choice of single- or multi-point, requir-
ing more than one calibration standard. A single-point calibration
gives good results in the range of values represented by the selected
calibration solution. When a wide range of values are expected, a
multi-point calibration is recommended.
With the sensor installed in the MP TROLL 9000 and immersed in
calibration solution, the sensor is powered at regular intervals and
its response is monitored. The difference (deviation) between the
minimum and maximum response over a predetermined time period
is tracked by the software. When the peaks of the response fall within
predetermined limits for the time period, the sensor response is
considered sufficiently stable to provide a valid calibration point. The
length of time and allowable deviation are specific to each sensor
type, and furthermore are specific to the determination of nominal
stability or complete stability. The time period of interest is shorter for
nominal stability than for complete stability, allowing for a shortening
of the calibration soak time while still returning a valid calibration point.
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and one or more calibration solutions for each parameter to be
calibrated. Suitable calibration solutions are supplied in In-Situ’s
individual calibration kits.
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SECTION 10: MONITORING WATER QUALITY: OVERVIEW