116
TROLL
9500
Operator’s Manual
0095110 rev. 007 01/09
SENSOR PREPARATION
To ensure optimum membrane response, the nitrate sensor should
be thoroughly hydrated in an appropriate solution before calibration. A
good way to do this is to allow the sensor to soak in the solution you
plan to use for the first calibration point (lowest concentration) for at
least 15 minutes and up to several days before calibration and use.
s PPM.FORCALIBRATIONINTHELOWERRANGECONCENTRATIONSLESS
than 14 ppm N)
s PPM.FORCALIBRATIONINTHEUPPERRANGECONCENTRATIONSOF
ppm N and up)
The sensor kit includes an empty bottle for this purpose.
SENSOR INSTALLATION
Unpack the nitrate sensor, hydrate it as above, and install in port 1,
2, or 3 in the sensor block at the front end of the MP TROLL 9500 as
follows.
TIP:
Remember that a polarographic D.O. sensor (if present)
will operate properly only in port 2 and a turbidity wiper
accessory only in port 3.
1. Remove the restrictor from the front end of the MP TROLL 9500.
This allows access to the sensor block depicted in the drawing
below.
2. Remove the sensor’s protective cap or storage bottle and set aside
for future storage of the sensor. If the connector end is covered
with a cap, remove it also.
3. Remove any moisture or dirt from the area around
the port where you will install the sensor, then use the
sensor removal tool to remove the plug from the port
where you will install the sensor.
4. Remove any moisture or dirt from the port connector with a clean
swab or tissue.
5. Check lubrication of the sensor o-rings.
TIP:
The sensor o-rings require generous lubrication before
installation. New sensors will be lubricated at the factory. If
the o-rings appear dry, apply apply a silicone lubricant before
installation.
6. Handling the sensor by the sides, not the tip, align the mark on the
side of the sensor with the mark on the port.
Avoid touching the membrane at the tip of the sensor.
Contaminants on the membrane can change its properties
and affect measurements.
7. Use the sensor insertion tool to firmly press the
sensor into the port until you feel it dock with the
connector at the bottom. When properly inserted a
small gap (width of the sensor removal tool) remains
between the widest part of the sensor and the instru-
ment body, for ease of removal.
CALIBRATION
OVERVIEW
The software offers several options for nitrate calibration.
s
Three-point bithermal
(“two-temperature”) calibration. The first
two calibration points are taken in solutions of different concentra-
tions at the same temperature. The third point uses one of these
SOLUTIONSATATEMPERATURETHATISATLEAST½HIGHERORLOWER
depending on anticipated fieldconditions. This type of calibration al-
lows determination of the sensor’s “isopotential point”—the ion con-
centration at which changes in temperature do not cause a change
in sensor response (voltage). A three-point bithermal calibration
is recommended before the first use of the sensor, and regularly
thereafter, to insure accurate readings at all potential temperatures.
s
Two-point isothermal
(“same temperature”) calibration using solu-
tions of two different concentrations. A two-point isothermal calibra-
tion calculates the sensor’s slope and offset but cannot compute
the isopotential point. For best results this type of calibration should
be carried out as close as possible to the temperature at which the
sensor will be used. Or, It may be performed after a previous three-
point bithermal calibration to recalculate the slope and offset of an
aging sensor while retaining the previously calculated isopotential
point.
sensor
removal
tool
sensor
insertion
tool
Pressure/turbidity
(or plug)
Temperature
Nitrate sensor may be installed
in port 1, 2, or 3
alignment mark
SECTION 17: NITRATE