Oxymax COS61
Device description
Hauser
19
5.3.1
Types of calibration
Types of calibration:
• Air (preferably saturated water vapor, e.g. near the water surface)
– Measured values between 70 and 130 %SAT result in the calibration of the measured value at
air
– Measured values smaller than 15 %SAT result in the calibration of the zero point
• Air-saturated water
– Like air calibration
• Reference measured value (entry at transmitter, sensor remains in the medium).
– Measured values between 50 and 150 %SAT result in the calibration of the measured value to
the reference value while maintaining the zero point
– Measured values smaller than 10 %SAT result in the calibration of the measured value to the
reference value while maintaining the measured value at air
If necessary, calibrate COS61 practically:
• In the
air
(water-vapor saturated) type of calibration in order to calibrate the
measured value at
air.
• In the
air-saturated water
type of calibration, but while using
oxygen-free
water, (see "Sensor
check" section), to calibrate the
zero point
.
5.3.2
Calibration intervals
You can determine the intervals with the following method:
1.
Check the sensor one month after its being put into operation:
– Remove the sensor from the medium.
– Clean the outside of the sensor with a damp cloth.
– Measure the oxygen saturation index at air after 20 minutes.
2.
Decide using the results:
a. If the measured value is not at 100 ±2 %SAT, you have to calibrate the sensor.
b. Otherwise, lengthen the time to the next inspection.
3.
Proceed as per Point 1 after two, four and/or eight months. In this way, you can determine
the optimum calibration interval for your sensor.
5.3.3
Calculation example for the calibration value
As a check, you can calculate the expected calibration value (transmitter display) as shown in the
following example (salinity is 0).
1.
Determine:
– The ambient temperature for the sensor (air temperature for "air" calibration method,water
temperature for "air-saturated water" calibration type)
– the altitude above sea level
– the current air pressure
L
(=rel. air pressure to sea level) at the time of calibration. (If
undeterminable, use 1013 hPa (407 inH
2
O) for an approximate calculation.)
2.
Define:
– the saturation value
S
acc. to the first table
– the factor
K
acc. to the second table
