TROLL 9500 Operator's Manual - Geotech Environmental Equipment

Multi-ParameterWater Quality TROLL ®AppendixElectronic Drift and Device RecalibrationThe electronics of the Multi-Parameter TROLL 9500 will experienceaccuracy drift over time. This drift applies to all channels and is additiveto the initial calibration accuracy. Electronic drift does not apply touser-calibrated sensors because the drift is compensated for duringcalibration.The system wide long-term drift is dominated by the stability of thevoltage reference used in the device. Other components exhibit longtermdrift of a much smaller magnitude.The equation used to calculate drift over time is:D = K ∗ √ (t / 1000 hours)where:D is the drift in ppmK is the long term stability coefficient listed as ppm / 1000 hoursbut actual units are ppmt is the time expressed in hoursUsing this information, the maximum drift over time is shown in thetable on this page.Determining DensityThe density of water in a well can be determined using an accuratetape measure and a pressure transducer. A change in pressure isrecorded between two points as the transducer is lowered into thewater and the corresponding change in depth is recorded using themeasuring tape. Density is then calculated using a simple formula.This method is valid if the pressure and depth measurements areaccurate and the water within the well is homogeneous throughout theentire depth of the well.TIP: The recommended frequency of factory recalibration ofthe MP TROLL 9500 depends upon the amount of drift auser is willing to tolerate. For example, if a drift of 0.025% isacceptable, then the recalibration period is 6 months; if a drift of0.05% is acceptable, then the recalibration period is 2 years.TROLL 9500 Operator’s Manual 1450095110 rev. 007 01/09