NIVELCO AnaCONT LE-100 Installation And Programming Manual

NIVELCO AnaCONT LE-100 Installation And Programming Manual Manual pdf 6 page image

6 / 60 le00100a0600p_05 BKI 11 ATEX 0012 X1.2.2. Characteristics of an ideal ORP electrode Negative voltage output in liquids with reduction potential, Positive voltage output in liquids with oxidation potential, Output voltage is equal to the redox potential (according to the Nernst equation) pH independent measurement with certain typesTo achieve reliable measurement and accuracy, these electrodes have to be thoroughly checked beforeinstallation and during usage from time to time. The time interval between two calibrations depends on theapplication and conditions where the ORP probes are used.1.2.3. Characteristics of an ideal DO sensorThe dissolved oxygen level indicates the amount (in mg/l or ppm) of physically dissolved gas-form oxygen inliquid phase.Oxygen-permeable membrane amperometric DC sensor wetted in the measurement medium gives outputcurrent proportional to the dissolved oxygen concentration of the medium.i airizeroOutput currentof the DO sensorDissolved oxygen (DO), ppm sat´n0Slope = /ppm oxygenOutput current of theDO sensorThe ideal DO sensor has: Izero=0, Temperature independent output currentReal DO sensor gives off a minimal I zero≠0ppm current in case of 0 ppm dissolved oxygen concentration and its oxygen-permeable capability is temperature-dependent. Oxygen-permeable capability of the membrane is increasing according to the increase of the temperature, at 25 °C it can be 4%/°C. Temperatureproportional correction is necessary for reliable measurement.The DO sensors in deed are not ideal (their properties depend on the design of the electrode, manufacturing tolerances and most of all the age of the electrode),so the parameters differ from the given values above. To give reliable DO measurement and accuracy these electrodes must be calibrated from time to time. Incase of DO sensors the calibration means that 0 ppm output value have to be set by offsetting in an oxygen-free solution. For DO measurement of othermediums (for example dry air 20.95%@25°C or oxygen-saturated water) adjustment of slope (nA/ppm) has to done accurately according to the properties ofthese mediums.