10
SENSOR SETUP
Each channel has its own sensor setup menu. The analyzer will select the appropriate menu for the
type of sensor that is currently connected to each channel.
DO Sensor
General
The Model 10 sensor has been designed to require very infrequent calibration. Unlike polaragraphic
systems, light fouling of the sensing element should not affect the accuracy of the reading, but should
only slow the response time of the system. (However, heavy biological fouling that prevents reasonable
sensor contact with the water will cause erroneous readings.) With the sensor kept reasonably clean, the
calibration should hold for 3 months to a year, depending upon conditions.
Note: The Model 10 D.O. sensor undergoes a thorough and
accurate test and calibration procedure before shipment
from the factory. Calibration of the D.O. reading at startup
is not necessary and is not recommended.
The MPA-48 analyzer allows the user to select from two different calibration procedures. The
procedure can be selected by choosing SETUP from the main menu. Once the SETUP menu appears,
use the arrow keys to choose the “SENSOR” option, and then select the desired sensor.
Sensor Calibration to a Reference
Calibration to a known reference is the easiest, simplest, and also the preferred method of calibration
when calibration is required. Calibration option number 1 “SENSOR REF CAL” allows the operator to
make adjustments to the D.O. reading to agree with any other source of D.O. information. THIS
CALIBRATION PROCEDURE MUST ONLY BE USED ON A CLEAN SENSOR. IF THE SENSOR IS
READING ERRONEOUSLY DUE TO HEAVY BIOLOGICAL FOULING, USE OF THIS CALIBRATION
METHOD WILL RESULT IN UNRELIABLE RESULTS. The sensor must be stable in the water to be
used as a reference before beginning this procedure. From the SENSOR SETUP menu, choose the
“Sensor Ref Cal” option, and press ENTER. The analyzer will now read the sensor for the period of time
indicated by the “dampening” parameter, and display the result as D.O. in PPM. If this result matches
the reference, simply press ENTER to exit. Otherwise, use the arrow keys to adjust the reading to match
the reference value, and then press ENTER to store this new value. This procedure is primarily an
adjustment to the offset value of the sensor, but an adjustment in slope will also be made when this
procedure is performed.
Sensor Slope Adjustment (NOT RECOMMENDED)
If performed correctly, the previously described “Sensor Calibration to a Reference” should be all
that is required by the user. “Sensor slope adjustment” should only be attempted upon recommendation
from the factory.
Sensor calibration option 2 “SENSOR SLOPE ADJ” allows the user to adjust the span of the sensor,
but this procedure must only be used immediately AFTER the sensor has been “zeroed” using calibration
option 1 with the sensor submerged in a zero oxygen solution. This zero solution may be prepared by
adding one tablespoon of sodium sulfite salt per liter of tap water in an open container (bucket). The
sodium sulfite salt will remove all oxygen from the water as it dissolves. Stir the water for about one
minute to dissolve the salt. Submerge the Model 10 sensor in this water and allow it to rest for at least
30 minutes. Make sure that no air bubbles are trapped on the face of the sensing element during the
soak. Once the sensor is stable, use the “Sensor Calibration to a Reference” procedure described
