CENSAR Technology (PPT 1.78 MB)

CENSAR Technology - Introduction© CENSAR 2002-2007*CENSAR TechnologyRoy MoorePresidentCENSAR Technologies, LLCBurlington, Iowa USACENSAR Technology - Introduction© CENSAR 2002-2007*CENSAR Device - Why?Use low cost printing technologiesMultiple sensorsLow costReproducibleSmallRobustNew measurement techniquesCENSAR Technology - Introduction© CENSAR 2002-2007*CENSAR Device - How?Thick film TechnologyScreen Printed and bakedSmallest Feature is 0.1mm gap or 0.2mm lineThin Film TechnologyIntegrated Circuit Manufacturing MethodPrinted and etchedSmallest features less than 0.001mmCENSAR Technology - Introduction© CENSAR 2002-2007*MeasurandsChlorineDissolved OxygenpHREDOXTemperatureConductivityCENSAR Technology - Introduction© CENSAR 2002-2007*“Electrical Connection to Ground”Reference ElectrodeCENSAR Technology - Introduction© CENSAR 2002-2007*Principles of Voltammetry:Uses three electrodes - WorkingCounterReferenceMaintain the working electrode at a fixed voltage with respect to the reference electrode. This voltage is chosen to oxidise or reduce the specific chemical of interest. The current flowing into the working electrode is proportional to concentrationCENSAR Technology - Introduction© CENSAR 2002-2007*Interfering Effects in voltammetry: Conductivity Temperature pH (for some species)CENSAR Technology - Introduction© CENSAR 2002-2007*ChlorineElectrochemical measurement -Voltammetric technique uses unique proton generator and microlines to measure chlorine and monchloramine, independently of flow and pHPROTON Generator - for pH adjustment and cleaningCalibrated against standard chemical method (DPD)CENSAR Technology - Introduction© CENSAR 2002-2007*Dissolved Oxygen (DO)Electrochemical measurement - Voltammetric technique, using the same basic technology as the chlorine sensor, but with different operating parameters.FLOW INDEPENDENT.Most DO meters require some small amount of flow to function properly. Only after 50 years of development are some low/no flow conventional DO sensors being released into the market.Calibration in de-ionised water at 0% and 100% saturation, standard temperatureCENSAR Technology - Introduction© CENSAR 2002-2007*pHGalvanometric TechniqueMeasure the voltage between the reference electrode and the pH electrode.Voltage is proportional to pHInterference from REDOX, some anions and temperature.Calibration in pH buffer at standard temperature near the expected operating conditionsCENSAR Technology - Introduction© CENSAR 2002-2007*REDOXGalvanometric techniqueMeasure the voltage between the reference electrode and a platinum electrode.REDOX potential is the voltage measuredTypically between +/-1.4VNo interferences, since REDOX is a general measure of the chemical nature of the water.High REDOX can indicate high chlorineLow REDOX might indicate corrosionIn general, if the REDOX moves, there is probably something wrong in the water.Calibration in standard solution and temperatureCENSAR Technology - Introduction© CENSAR 2002-2007*TemperatureStandard solid state sensor built into probe - one time only calibration, but slow response.Can be used in modelling to indicate ageHigh temperature reduces the life of chlorineUsed to correct the other measurementsCENSAR Technology - Introduction© CENSAR 2002-2007*ConductivityMeasure of amount of dissolved ions in the water (hard water - high conductivity, soft water - low conductivity)Use four electrodes - measure the current required between one pair to maintain a constant voltage across a second pair - (standard 4 electrode resistance measurement).Can be calibrated to give dissolved solidsUsed to distinguish water from different sourcesAlso can be used to correct other measurementsCalibration in standard solution at fixed temperatureCENSAR Technology - Introduction© CENSAR 2002-2007*Reference ElectrodeSilver/Silver Chloride typeNew technology - can be left dry without losing salt - short hydration time of a few minutesCENSAR Technology - Introduction© CENSAR 2002-2007*Power SupplyLow NoiseMust be Isolated - even from other probes on the same system custom battery or mains supply is availableCENSAR Technology - Introduction© CENSAR 2002-2007*Limitations of the technologyVery acidic environmentsVery alkalineHigh content of suspended solids (especially organics) or contaminantsHigh temperatures (limitation of the reference)Some chemicals will attack the sensorsCENSAR Technology - Introduction© CENSAR 2002-2007*Care of the DeviceDO NOT TOUCH the sensing surfaceDO NOT APPLY silicone or other grease to the o-ringsHandle by the edge onlyDO NOT try to clean the chipDO NOT leave the reference electrode in a hot location (e.g. car dashboard)CENSAR Technology - Introduction© CENSAR 2002-2007*PrecautionsFollow the correct hydration procedure during installationIf the probe is removed it should be rinsed in clean water or kept in a weak solution (a few mg/l of Cl) of sodium dichloroisocyanurate (e.g. instachlor)Do not get water on the connection pins or in the reference electrode holeCENSAR Technology - Introduction© CENSAR 2002-2007*Summary and Questions.CENSAR - Low cost, multi-sensor technology.Some measurands better, some notIn all cases, the overall device is smaller and more robust than competing technologiesIn some cases, the sensors are an improvement over traditional technologies1