TROLL 9500 Operator's Manual - Geotech Environmental Equipment

Section 18: TurbidityManual WipeTo wipe the turbidity sensor optics manually:1. With the wiper installed in port 3, connect the MP TROLL 9500 to aPC and establish a connection in Win-Situ 4 or Pocket-Situ 4.2. Select the Wiper in the Navigation tree.23. Click Wipe. The wiper will pass once over the turbidity sensoroptics and return to its home position.Wiper Guidelines and Precautions• If a wiper is installed during a Quick Cal of the Basic sensors (seeSection 3, Getting Started), steps should be taken to insure thewiper pad material does not absorb the Quick Cal solution. Thereare two ways to do this.– Remove the wiper head before doing the Quick Cal. Refer toWiper Maintenance guidelines later in this section for instructionson removing the wiper head.– Alternatively, soak the front end of the instrument in plain waterbefore calibrating to allow the wiping pad to absorb sufficientwater to prevent its absorbing any Quick Cal solution.• Do not attempt to move the wiper head by hand. Wiper movementis software-controlled.• The wiper pressure may be adjusted if necessary so that the padis effectively cleaning the sapphire windows of the turbidity sensorduring movement. Refer to Wiper Maintenance guidelines later inthis section.• The wiper pad or head may be replaced as needed. Refer to WiperMaintenance guidelines later in this section.• When an RDO optical dissolved oxygen sensor is installed, checkto see that the RDO adapter cable is out of the way of wiper movement.3CalibrationFactory CalibrationThe turbidity sensor has been factory-calibrated to achieve a sensoraccuracy of ± 5% or 2 NTU (whichever is greater). The sensor iscalibrated over its full range, 0 to 2000 NTU, using polymer standards.The resulting calibration coefficients are written to the sensor memory,where they are stored permanently. They may be overlaid by performinga field calibration as described below, or may be recalled from thesensor memory at any time.The MP TROLL 9500’s turbidity sensor is ready to measure turbiditywithout any user intervention. It is advisable to take a turbidity readingfirst in your own calibration solution(s) as a check to ensure the accuracyis within your operational standards and requirements. If thisresult is satisfactory, a field calibration is not required.Field CalibrationField calibration (or “user calibration”) is an overlay function that isapplied after the factory calibration math is done. The factory calibrationapplies across the entire range of NTU, and can be altered in thefield with a 1 to 4 point calibration procedure as described below tocompensate for effects of sensor fouling and other factors. You maywish to perform a field calibration with standards other than polymer(i.e., Formazin).For best results, calibrate as close to field temperature as possible.Calibration SolutionsA nephelometer such as the In-Situ turbidity sensor should becalibrated using standard reference suspensions having reproduciblelight-scattering properties. The sensor has been factory-calibratedwith polymer suspensions, and the resulting calibration coefficientstake into account the light-scattering properties of the suspensionsand the sensor optics.Q:A:Why do I need to calibrate the turbidity sensor if ithas been calibrated in the factory?A new turbidity sensor is ready to measure turbidity withreference to suspended polymer standards. If you preferto reference turbidity measurements to Formazin ratherthan polymer, a field calibration with Formazin should beperformed.After cleaning the sensor, readings should be checkedwith standards and a field calibration performed ifnecessary.TROLL 9500 Operator’s Manual 1240095110 rev. 007 01/09