Eureka Manta Manual Page 62 of 67
2 How often should you calibrate your multiprobe?
That depends on a number of factors, including the nature of the waters being monitored and your
expectations for accuracy. We suggest that you start by calibrating once per week and shorten or
lengthen that interval as the data suggest. (D.2)
3 How Do I Choose Calibration Standards?
For best results, choose a calibration standard whose value is close to what you expect to see in the
field. For example, calibrate with a 1413 μS Specific Conductance standard if you expect to see
Specific Conductances between 500 and 1000 μS in the field. Don’t calibrate with a sea water
standard. And if your waters tend toward the acidic, calibrate with a 4-buffer instead of a 10-buffer.
If you are moving your multiprobe across wide ranges of water conditions, you may wish to recalibrate
to match the new situations. For instance, if you are measuring a clear lake during the morning and
a high-sediment stream in the afternoon, you might consider recalibrating at noon with a high-range
turbidity standard. (D.3)
4 What is an SRF?
Suppose that a typical Conductivity sensor reports 100 μA in a 1413 μS/cm standard. If your particular
Conductivity sensor reports 100 μA in that same calibration solution, then your SRF is 100% (some
parameters, such as pH, have a more complex SRF calculation, but the effect is the same). If your
response is 80 μA, your SRF would be 80%. When you click the OK button to accept a calibration, the
Manta automatically accepts your calibration if the SRF is between 60% and 140%. If the SRF falls
outside that range, you will be cautioned to check your standard value, make sure the sensor is clean,
make sure the reading has stabilized, etc. But you can elect to accept any SRF.
Each sensor calibration’s Sensor Response Factor (SRF) is automatically logged into the Cal Record
with the details of that calibration. (D.5)
5 Do I Have to Calibrate Temperature?
No; the Temperature sensor is so stable that it needs no calibration. (D.6)
6 What is the Basic Calibration Procedure?
The Manta never guesses parameter values, so you have to calibrate it from time to time by simply
telling the instrument what it should read in a known calibration situation. The general procedure is
shown below. (D.2)
1) Clean the sensor and perform any necessary sensor-specific maintenance.
2) Select a calibration standard whose value is close to the values you expect to see in the field.
3) Rinse sensors thoroughly (more than once may be required) with DI (deionized) water, especially
if you have been using other calibration solutions. Shake the Manta so the DI can vigorously
remove traces of old calibration solutions and cleaning agents – repeat if necessary.
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