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Roy Moore

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Thin Film Technology. Integrated Circuit Manufacturing Method. Printed and etched ... DO NOT leave the reference electrode in a hot location (e.g. car dashboard) ... – PowerPoint PPT presentation

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Title: Roy Moore


1
CENSAR Technology
  • Roy Moore
  • President
  • CENSAR Technologies, LLC
  • Burlington, Iowa USA

2
CENSAR Device - Why?
  • Use low cost printing technologies
  • Multiple sensors
  • Low cost
  • Reproducible
  • Small
  • Robust
  • New measurement techniques

3
CENSAR Device - How?
  • Thick film Technology
  • Screen Printed and baked
  • Smallest Feature is 0.1mm gap or 0.2mm line
  • Thin Film Technology
  • Integrated Circuit Manufacturing Method
  • Printed and etched
  • Smallest features less than 0.001mm

4
Measurands
  • Chlorine
  • Dissolved Oxygen
  • pH
  • REDOX
  • Temperature
  • Conductivity

5
Electrical Connection to Ground
  • Reference Electrode

6
Principles of Voltammetry
  • Uses three electrodes -
  • Working
  • Counter
  • Reference
  • Maintain 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 concentration!

7
Interfering Effects in voltammetry
  • Conductivity
  • Temperature
  • pH (for some species)

8
Chlorine
  • Electrochemical measurement -
  • Voltammetric technique uses unique proton
    generator and microlines to measure chlorine and
    monchloramine, independently of flow and pH
  • PROTON Generator - for pH adjustment and cleaning
  • Calibrated against standard chemical method (DPD)

9
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 temperature

10
pH
  • Galvanometric Technique
  • Measure the voltage between the reference
    electrode and the pH electrode.
  • Voltage is proportional to pH
  • Interference from REDOX, some anions and
    temperature.
  • Calibration in pH buffer at standard temperature
    near the expected operating conditions

11
REDOX
  • Galvanometric technique
  • Measure the voltage between the reference
    electrode and a platinum electrode.
  • REDOX potential is the voltage measured
  • Typically between /-1.4V
  • No interferences, since REDOX is a general
    measure of the chemical nature of the water.
  • High REDOX can indicate high chlorine
  • Low REDOX might indicate corrosion
  • In general, if the REDOX moves, there is probably
    something wrong in the water.
  • Calibration in standard solution and temperature

12
Temperature
  • Standard solid state sensor built into probe -
    one time only calibration, but slow response.
  • Can be used in modelling to indicate age
  • High temperature reduces the life of chlorine
  • Used to correct the other measurements

13
Conductivity
  • Measure 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 solids
  • Used to distinguish water from different sources
  • Also can be used to correct other measurements
  • Calibration in standard solution at fixed
    temperature

14
Reference Electrode
  • Silver/Silver Chloride type
  • New technology
  • - can be left dry without losing salt
  • - short hydration time of a few minutes

15
Power Supply
  • Low Noise
  • Must be Isolated -
  • even from other probes on the same system
  • custom battery or mains supply is available

16
Limitations of the technology
  • Very acidic environments
  • Very alkaline
  • High content of suspended solids (especially
    organics) or contaminants
  • High temperatures (limitation of the reference)
  • Some chemicals will attack the sensors

17
Care of the Device
  • DO NOT TOUCH the sensing surface
  • DO NOT APPLY silicone or other grease to the
    o-rings
  • Handle by the edge only
  • DO NOT try to clean the chip
  • DO NOT leave the reference electrode in a hot
    location (e.g. car dashboard)

18
Precautions
  • Follow the correct hydration procedure during
    installation
  • If 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 hole

19
Summary and Questions.
  • CENSAR - Low cost, multi-sensor technology.
  • Some measurands better, some not
  • In all cases, the overall device is smaller and
    more robust than competing technologies
  • In some cases, the sensors are an improvement
    over traditional technologies
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