In-Situ TROLL 9500 Operators Manual - Manual (Page 105)

98
TROLL 9500 Operator’s Manual 0095110 rev. 007 01/09
sensor
removal
tool
Pressure/Turbidity
(or plug)
Temperature
Install pH/ORP
sensor in
port 1 only
alignment mark
pH/ORP Sensor Position
F is Faraday’s constant,
T is the temperature in Kelvin,
n is the number of electrons,
[ox] is the oxidant concentration in moles/L, and
[red] is the reductant concentration in moles/L.
Most natural waters contain many species that are involved in the
redox process so that it is not possible to calculate the ORP using
the Nernst equation. All redox species do however reach equilib-
rium. A Standard solution of known redox potential for a particular
ORP electrode is used to calibrate ORP. The sensor then gives a
calibrated response in mV when placed in a sample.
SENSOR INSTALLATION
The MP TROLL 9500 may be shipped with a pH/ORP sensor
installed. If installation is necessary, unpack and install the sensor in
port 1 of the MP TROLL 9500 as follows.
The combination pH/ORP sensor will work properly only
in port 1.
TIP: To ensure optimum response for a new or previously
stored sensor, rinse off the soaking solution, then soak the
sensor in clean water for at least 15 minutes before calibrating.
1. Remove the restrictor or Cal Cup from the front end of the TROLL
9500. This allows access to the sensor block shown below.
2. Remove the sensor hydration bottle and set aside for future use.
3. Rinse the sensor in clean water to remove the soaking solution.
Soak the sensor in clean water for at least 15 minutes before
calibrating.
4. Remove any moisture or dirt from the area around
port 1, then use the sensor removal tool to remove
the plug from the port. Retain the plug for future use.
5. Remove any moisture or dirt from the port connector with a clean
swab or tissue.
6. Remove the cap from the sensor connector. Check lubrication of
the o-rings. If they appear dry, apply a silicone lubricant.
7. Visually align the sensor connector pins with the port connector
pins.
8. Press the sensor firmly into the port until you feel it dock with the
port connector. When properly inserted a small gap (the width of
the sensor removal tool) remains between the widest part of the
sensor and the instrument body, for ease of removal.
CALIBRATION
OVERVIEW
A one-point calibration in a solution with a known potential at a given
temperature is sufficient to calibrate ORP. Software options:
s
and conductivity) at one time with one solution.
s
specifically formulated for calibrating ORP. Results in calculation of
sensor offset.
s
solutions are required.
Nominal vs. Stable
To shorten the calibration time, you have the option to accept the
calibration when “Nominal” stability conditions are achieved. If the
early value is accepted, the calibration point will be designated “USER
SET” in the calibration report. If the calibration was performed through
to stability (“STABLE” in the calibration report), the sensor will operate
as intended by In-Situ’s quality standards.
CALIBRATION SOLUTIONS
Only one solution is required for ORP calibration. Quick Cal and
ZoBell’s solution are available from In-Situ Inc. A custom solution may
be used in a Traditional calibration if its milliVolt value at the calibra-
tion temperature is known.
Please note that a pH/ORP sensor requires separate calibra-
tions for pH and ORP. The Quick Cal procedure produces
excellent results for ORP so long as the solution is stored as
recommended and used before its expiration date. After performing a
Quick Cal for ORP, we recommend a 2- or 3-point Traditional
calibration for pH, as described in Section 11 of this manual.
SECTION 14: ORP