DEW-POINT SENSOR TRAINING. Moisture Sensors DP & Rh The basic low cost solution With a wide range

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Edwina Dawson
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1 Moisture Sensors DP & Rh The basic low cost solution With a wide range

Moisture technologies and their ranges DEW-POINT SENSOR TRAINING No single technology can cover the entire range All have limitations Impedance and capacitive sensors have certain key advantages

2 Moisture technologies and their ranges DEW-POINT SENSOR TRAINING No single technology can cover the entire range All have limitations Impedance and capacitive sensors have certain key advantages TDL Quartz Sensors Chilled Mirror Hygrometer Impedance Dew-Point Sensors RH Sensors Dew Point o C 10ppb V 10ppm V 1000pp 23000ppm V 20 % V/V >50 % V/V m V

3 2 Technologies IMPEDANCE DEW-POINT SENSOR TRAINING Ceramic nanofarad Polymer Picofarad -100C -20C +60 C Impedance Capacitive

4 Impedance Technology Most widely used in industry Rugged-can work at high pressure Simple and compact Inexpensive Wide measurement range -100 to +20 C DP Ceramic AlOx Less accurate than Cooled Mirror Can be affected by contaminants

5 Capacitive sensor technology DEW-POINT SENSOR TRAINING Polymer Rh & Dew Point - Adsorption of humidity into a porous polymer film - Direct electrical response to changes in relative humidity. - Ambient temperature MUST be measured and recorded to give readings and validity. Fast response Higher dew points -60 to +60 C DP

6 Installation Considerations and Sampling Systems Get the sample system wrong-the answer will never be correct (No matter what technology you use!)

7 General Considerations for the Installation of Dewpoint Systems Materials used Magnitude & direction of step change for moisture System leakage Design to avoid dead spaces, etc Consider flow rates and pressure Volume in the sample system Protect against contamination particles and liquids For high dewpoint sampling, avoid condensation

8 Sample system: materials DEW-POINT SENSOR TRAINING Moisture is polar and stick to surfaces It is not just the sample system that can affect response Rough surfaces increase effective surface area

9 Magnitude and step change Very dry systems: <-80 C Wetting up can be slow - adsorption onto system components starts first - Keep all tubing to a minimum length and size - If high alarms are set then use tight limits Low range systems: -60 to -25 C Wetting up now occurs more quickly, less time lag - If alarms are to be set allow more of a buffer DEW-POINT SENSOR TRAINING Middle range systems: -25 to 0 C Wetting up is now very fast - Set alarms close to the stated limits - Allow process correction to occur more quickly - Helps avoid potential sensor damage or select a mid range senor Upper range system: -20 to +60 C Dry down and wet up are both quick - set tight alarms to overcome process lag

10 Careful Design Ensure smallest possible volume Avoid dead spaces they are hard to flush Avoid too many connections & components Leaks will slow system response and design level for moisture is never reached.

11 Testing for leaks Simplest test..alter the flow.. If the flow increase and moisture decrease it is probably a leak. Dry process systems (<-70 C) helium leak check -60 to -25 C and pressurised: Use a soap solution sparingly -50 to +20 C: Hard to find by flow changes, try dry pressure testing with a sensitive gauge -25 to +25 C: Hard to find by flow change, careful checking of all unions required.

12 Flow Rate Flow Rate. The flow rate must be in the correct range. Flow rate too low:-ineffective purging -Accentuates absorption & desorption -Back migration of moisture Slow response High Readings Flow Rate to high:- Problems with back pressure and slow response Systems with high volumes and low flows should be avoided. Check the flow rate of the device you want to use!!!!

13 Pressure effects Dew point varies with changes in pressure Try to operate in the middle of its moisture range to get best response Sampling at pressure will help this

14 Avoid contamination using filters filters DEW-POINT SENSOR TRAINING

15 Avoid Condensation At high dew points there is always a risk of condensation forming. This can be avoided by:- Close control of temperature (keep well above dew point) Avoid cold spots in system Trace heating if necessary

16 Diurnal temperature effects DEW-POINT SENSOR TRAINING

18 Examples of Installations and Sampling Systems: Direct Insertion Monitor Flow Velocity: Max 20m/sec for impedance Max 1m/sec for DEWMET, 5m/sec with sintered guard (flow baffle and coarse particle protection) or membrane guard (fine particle protection)

19 Examples of Installations and Sampling Systems: Sampling with Suction Pump from Near Atmospheric Pressure Cooling Coil (if required) Diaphragm Pump

20 Examples of Installations and Sampling Systems: On-line, Remote Sampling Particulate and/or Coalescing Filter (if required) Flow Monitoring 5NL/min impedance 0.5NL/min Cooled Mirror Vent Vent Isolation Valve Pressure Let-down Regulator (if > 10barg) Max 300barg impedance 100barg DEWMET atmospheric Pressure Dew Process Pressure Dew Atmospheric

21 Examples of Installations and Sampling Systems: Elevated Temperature Sampling for High Dew-point Measurements with Cooled Mirror Elevated Temperature Sample Enclosure Filter (if required) Trace Heated, Temperature Controlled Sample Tubing * or alternatively, if process temperature is less than +85 o C, Direct Insertion as first example Hot Heat Suction Pump (if required)

22 Simple sampling systems Easidew Sampler Standard range 10b (options to 69b) Filter-particulate Simple flow regulator but no flow meter Allows sampling at pressure or atmosphere Can be used with all Michell hygrometers

23 Drycheck Fully self contained Particulate filtration Flow meter Can be used at atmospheric or pressure up to 10 bar LCD Display

24 ES20 Build off a data sheet Different components can be added Choice of enclosures or none at all Can use IS/IEC rated hygrometers Pressures up to 20 bar Pressure or atmospheric measurement Instrument air Compressed air Medical gases Breathing air

25 Dew-Point Transmitter Products DEW-POINT SENSOR TRAINING IMPEDANCE Hygrometer application

26 Selecting hygrometers The list below is a general check list of what should be considered... Range Resolution Accuracy ppm will vary with C Response time Stability Media- gas or liquid, contaminants, aggressive chemicals Hazardous area rating- Eexd, IS Outputs - ma as C or ppm, RS485/Modbus Location Indoor/outdoor, weather conditions Local support Calibration

Dew-Point Transmitter Building Blocks IMPEDANCE A DEW-POINT SENSOR TRAINING Sensor packaging, type and range will decide suitability for use Mating Conn.

27 Dew-Point Transmitter Building Blocks IMPEDANCE A DEW-POINT SENSOR TRAINING Sensor packaging, type and range will decide suitability for use Mating Conn. Electrical Conn. Electronics Glass Metal Seal Tile Technology Guard Mini DIN PCB Mini DIN 3 wire digital 2 wire 4 to 20 ma 450 bar 20 bar Ceramic Imped. Polymer HDPE or Sintered

Dew Point Application: Compressed Air Process Plant Pneumatic tools Valve control Pneumatic press equipment Breathing air High pressure air systems Automotive (train, bus etc.

28 Dew Point Application: Compressed Air Process Plant Pneumatic tools Valve control Pneumatic press equipment Breathing air High pressure air systems Automotive (train, bus etc.) Excess moisture causes: Premature wear & tear Rust and corrosion in piping and systems Damage to instruments Spoiled paint surfaces in spray booths Increase in scrap rate Potential impact on safety and health

29 What happens when air is compressed Compress air by 7 B = 800% increase in contamination Contaminants come from: Dirt, dusts and other particulates Water vapour Unburned hydrocarbons and oils Oxide and chlorine bases forming caustic gases

30 Compressed air standard ISO Class micron Solid Particles micron micron Water Pressure DP Oil Mg/m3 Inc vapour ,000 1, Not specified Not specified Not specified 10, Not specified Not specified 1, ,00 0 Not specified Not specified Not specified 10 7 Not specified Not specified

31 Types of dryer Refrigerant - Typically gives 2-4 C Dessicant - Typically gives -40 to -70 C Membrane

Air or Gas Dryers DEW-POINT SENSOR TRAINING Compressed Air Dryers Plastic Moulding Dryers Dryers for Ozone Generators Pure Gas Dryers Breathing Air Dryers Measurement

32 Air or Gas Dryers DEW-POINT SENSOR TRAINING Compressed Air Dryers Plastic Moulding Dryers Dryers for Ozone Generators Pure Gas Dryers Breathing Air Dryers Measurement Monitoring of dewpoint at outlet of dryer to ensure specification. Control of regenerative dryers switchover to increase efficiency and save energy costs Spot check of dryer outputs

33 Adsorption Principle DEW-POINT SENSOR TRAINING Regenerated Tower Drying Tower

34 Rotary Adsorption Dryer Hot unsaturated air for regeneration Hot saturated air Dry air Cold saturated air

35 Refrigeration Dryer AIR/AIR HEAT EXCH

Power Generation Hydrogen Coolant Moisture in hydrogen being used to cool electrical generator sets Measurement Techniques: Ensuring that the dewpoint of the hydrogen does not rise above ambient

36 Power Generation Hydrogen Coolant Moisture in hydrogen being used to cool electrical generator sets Measurement Techniques: Ensuring that the dewpoint of the hydrogen does not rise above ambient temperature causing condensation and thus the danger of damaging the generator. Upper limit is usually 0oC dewpoint. Checking outlet from H2 adsorption dryer Limit -20 C dp at operating pressure (typically 4 barg) Checking outlet from generator frame Limit 0 C dp at frame pressure (typically 2 to 4 barg)

Power Generation Application Moisture in Sulphur

severe deterioration of high-voltage switchgear.

SF6 in cylinders by industrial gas producers prior to use

37 Power Generation Application Moisture in Sulphur hexafluoride (SF6) arc quenching gas can cause rapid and severe deterioration of high-voltage switchgear. Measurement Techniques: Checking the moisture content of new SF6 in cylinders by industrial gas producers prior to use Dry gas purging of new switchgear enclosures In service field checks/ continuous monitoring

38 Power Generation DEW-POINT SENSOR TRAINING GAS TURBINES It is important to monitor the dewpoint of the inlet air of a gas turbine in order to ensure that ice does not form on the turbine blades.

cylinders (top picture) filled at a central filling station or in bulk (bottom) from an

39 Industrial Gases Compressed gases are supplied to many industrial and research users by a relatively small number of large gas companies, for example: The gases are supplied either in cylinders (top picture) filled at a central filling station or in bulk (bottom) from an on-site generation plant, often managed by the gas supplier Gas Cylinder Checking Gas Generation Plant

condensation Temperature range 20 to 35 C Humidity range 60-100%

40 Swimming Pool Dehumidifier DEW-POINT SENSOR TRAINING Rh Products and Applications Monitoring ambient humidity for control to prevent condensation Temperature range 20 to 35 C Humidity range % Sensors need to work well as they must have a good resistance to Chlorine

41 Weather Station Provide the %RH monitoring for Delta-T s weather station Humidity range %RH Temperature range -30 to 70 C

42 Salt Spray Chamber Humidity monitoring in corrosion chamber to speed up the ageing process of mechanical parts Humidity range 0-85%RH Temperature range 5 to 30 C

43 Fish Smoker Humidity monitoring of smoke circulation in fish smoker High humidity - up to 100%RH Temperature ranges from 50 C up to 150 C depending on application

be controlled at 97%RH for potatoes, much less for

44 Agricultural Food Storage Monitoring humidity for control in grain & potato stores Humidity needs to be controlled at 97%RH for potatoes, much less for grain Temperatures vary with the ambient condition

45 Fume Cupboards & glove boxes Monitoring ambient humidity within a fume cupboard Humidity range %RH Temperatures are only ambient room conditions

46 Wood Kiln Drying Monitoring of humidity for control and efficiency of the drying system Humidity range 20-75%RH Temperature range 25 to 100 C dependant on application Can also apply to ceramics and brick drying

47 Engine Test Cell Monitoring humidity of the air intake to the engine Humidity range 20-95%RH Temperature range 15 to 50 C Can apply to automotive and marine engines

48 Questions? DEW-POINT SENSOR TRAINING

Dew-Point Transmitters and Instruments

Dew-Point Transmitters and Instruments Reliable moisture measurement for critical process control Moisture Measurement and Analysis Michell Instruments sensors provide accurate and reliable moisture measurement