Post on 24-Dec-2015
transcript
Monitoring Systems
Gaseous Pollutants mini-courseTAMS Center February 2009
Can Be Simple
Source: CTUIR Ozone QAPP
Temp Sensor
Can Be More Complex
Cherokee Nation Ambient Air Monitoring
Meteorological
FRM PM 2.5 Sampler
(Filter Based)
Air Quality Monitoring Shelter
Inside the Monitoring Shelter
Gas Analyzer Rack
Data Logger
Calibrator
Continuous Particulate
Monitor Control Units
Zero Air Generator
NOy
NOx
SO2
Ozone
Toxics Flow Controller
Continuous Particulate Sensor Unit
Vertical manifold
Tubing for NOy
The First Rule: Make everything at the monitoring site as easy to get to as possible. If it’s hard, the quality of your data
may suffer.
What’s materials are allowed? Teflon and borosilicate glass (Pyrex)Types of Teflon: PTFE, FEP, PFA
Compression Union Tee
StopcockCompression Union
Cap Nut (seal)
Ferrule nutCompression Union Reducer
Compression to NPT adapter
Use FEP (clear) ¼ inch Outside Diameter tubing. Typical inside diameters are 1/8, 5/32 and 3/16.
1/8 inch ID can restrict flow (1/8 = 0.125) (thick wall)5/32 is middle ground (5/32 = 0.156) 3/16 inch ID kinks easily (3/16 = 0.186) (thin wall)
Possible water trap
http://www.savillex.com/catalog/index.php
Residence time must be less than 20 seconds and should be less than 10 seconds
In order to collect air for analysis at the minimum required 3-meter height from ground level, the air entering the analyzer must be captured and moved to the analyzer without causing any condition that will change the composition of the sample air. All components of the sample collection system that contacts sample air will be made of Pyrex glass or Teflon to minimize the potential for reaction once air enters the system. Also, all components in the sample collection system will be replaced or cleaned at least quarterly. Residence time, the time from when air enters the system until it enters the analyzer, will be kept below EPA’s maximum recommended 10 seconds (EPA requires residence time not to exceed 20 seconds). CTUIR will use 5/32 inch inside diameter and 1/4 inch outside diameter Teflon tubing as the intake probe. The maximum tubing length at the maximum 10 second residence time is calculated as follows.
The residence time section of the CTUIR Ozone QAPP
To calculate the maximum total system collection volume in liters while achieving a 10-second residence time when flow is 0.5 liters per minute0.5 Liters per minute * (1 minute/60 seconds) = 0.00833 liters per second 0.00833 liters per second * 10 seconds = 0.0833 liters To calculate volume in liters per foot of tubing5/32 inches (tubing inside diameter) = 0.15625 inches = 0.01302 feetArea of tubing opening = 3.1416 * (0.01302/2)2 = 0.0001331 square feet0.0001331 square feet = 0.0001331 cubic feet in 1-foot of tubing length. 0.0001331 ft3 * (28.31685 liters / 1 ft3) = 0.003769 liters of volume per foot of 5/32 ID tubing Water TrapSince the air may be cooled in the climate controlled enclosure and this process may condense moisture, and/or rain may enter the sample collection system under extreme conditions, a water trap may be needed to protect the equipment. CTUIR will use a glass water trap no larger than 25ml (.025 liters).
Source: CTUIR Ozone QAPP
Maximum tubing lengthMax tubing volume = (Maximum allowed total intake system volume) - (volume of water trap)0.0833 liters - 0.025 liters = 0.0583 litersMaximum tubing length in feet = (max tubing volume) / (tubing volume per foot)0.0583 liters / (.003769 liters/foot) = 15.47 feet of tubing To ensure an acceptable residence time CTUIR will limit the 5/32-inch ID tubing length to 15 feet or less and will not exceed 25ml volume in the water trap.
Source: CTUIR Ozone QAPP
In this instance we wanted to know the maximum length of tubing we could use and still maintain a 10 second residence time at a flow rate of 0.5 liters per minute if we put a 25ml water trap in the line.
So, what did we do?
1.We determined the maximum volume of air the analyzer would use in 10 seconds.2.We calculated the volume in 1 foot of our tubing (V = pi * (d/2)2 * L) 3.We subtracted the water trap volume from the maximum volume in step 14.Then we divided the remaining volume from step 3 by the volume per foot of tubing
The rest was just getting things into the same units
Small Pump
Ozone Analyzer
Water trap and long line¼-Inch Teflon tubing
Teflon Compression Tee
Need a longer line?Use a small pump to decrease residence time
Caution: warm moist air may condense when inside an air conditioned shelter.
Anemometer measures wind speed
Calibration SystemDon’t pressurize analyzers; you must vent. Total flow from calibrator must exceed combined analyzer demand
Calibrator
Analyzer Analyzer Analyzer
Vent
Zero Air
Exhaust manifold
Cal gasmust pass through filter
Wall
Insect screen
Regulator(2 stage stainless steel match fittings & purge
CGA 660)
EPA Protocol GasMost have 2-year certification
Source: CTUIR Ozone QAPP
Each monitoring organization must have at least one Local Primary Standard which serves as the point of traceability (comparison) for each ozone analyzer used by that monitoring organization. The LPS must include an ozone generator, an output port or manifold, an UV photometer and a zero air source, and must be verified to be within limits of the average of six comparisons between it and the EPA SRP, and the result of each concentration’s comparison must be less than + 4% (relative percent difference) AND + 4 ppb. The Local Primary Standard can be used for routine verifications (span checks) of local equipment as long as the requirements for the LPS are met, including the restriction that the LPS never measures ambient air, etc. However, audits must be performed with a system that is two levels of authority removed from the LPS; e.g., the LPS is calibrated to the EPA SRP, and the audit equipment is verified against a DIFFERENT EPA SRP.
20 to 30 degrees Celsius
Probe Siting
Difference in height
2X Difference in height
270 degrees must beopen at 30 degrees from horizontal
Obstacle1/3 of 90 degrees
Datalogger and data flow
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ReportingData
StorageTelemetry System
PC System or Data Logger
Monitors
Calibration System
Data Validation
Data flow in Ambient Air Monitoring Systems
Graphic Courtesy of U.S. EPA Office of Air Quality Planning and Standards -Nealson Watkins & Lewis Weinstock
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Common Types of Datalogger Communication
• Analog– Instrument outputs a voltage– Datalogger senses voltage– Both must know what the voltage represents
• The range of voltage used, and the concentration range of the instrument must be coordinated between the datalogger and the instrument
• Digital– Direct communication – data streams
• Compatibility and connection/communication parameters• Current
– Instrument outputs current– Current is passed through a close tolerance resistor– Datalogger senses voltage drop across the resistor
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Basic Analog Concept
Voltage PPM Voltage PPM
10 Volts 0.500 ppm
Full Scale
If 10 volts = 0.500 ppmThen 5 volts = 0.250 ppm
5 Volts 0.250 ppm
Change is proportional
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Basic Analog Concept
Voltage PPM Voltage PPM
10 Volts 0.500 ppm
Full Scale
If 10 volts = 0.500 ppmThen 1 volt = 0.050 ppm
1 Volt 0.050 ppm
Change is proportional
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MultiplierFull range of analyzer/sensor
Full range of voltage = Multiplier
0.500 ppm
2.5 volts= 0.2 ppm / volt
Example: An ozone analyzer is set to a full scale of 0.500 ppm, and it’s analog output is set to a full scale of 2.5 volts
If the datalogger sees a voltage of 0.67 it will have to multiply the voltage by the multiplier to get the concentration
0.67 volts X 0.2 ppm/volt = 0.134 ppm
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Analog Example
Full Scale 0.500 PPM2.5 Volts Datalogger
Monitor
0.134 ppm
.134 ppm / 0.500 ppm = 0.2680.268 x 2.5 volts = 0.67 volts
0.67 volt
Multiplier = 0.500 ppm / 2.5 volts = 0.2 ppm / volt0.2 ppm/volt X 0.67 volt = 0.134 ppm
0.67volt
Converts digital concentration to a voltage output
0.134 ppm
Converts the voltage to a digital concentration and logs it
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Datalogger Configuration Differences
• Some dataloggers need a multiplier and an offset for configuration
• ESC asks for:– Volts High Input– Volts Low Input– High Output E.U.s– Low Output E.U.sAnd then calculates multiplier and offset
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Analog Examples
ESC
Where is the wire connected?
Analog outputs on API Teledyne NOx analyzerNOx, NO2, NO, Status
Datalogger analog in
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Analog ExamplesCampbell
Where is the wire connected?
Volt rangePPB Range 500Volts 5000 mV
500
5000= 0.1
UNITS !!!
Multiplier
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Single Ended & Differential Voltage(Campbell Scientific – SE & DIFF)
2.5 VoltsDatalogger
2.4 VoltsDatalogger
Ground
.1 Volt(L)
2.5 Volts(H)
Differentialmeasures betweentwo voltages
2.5 Volts
Single Endedmeasures betweenSE terminal and ground
Sensor Sensor
1
H L
Diff
SE 1 2
(Differential Channel 1)
(Screw on datalogger)
(Single ended channel 2)
Zeno has A, B and C in their configuration.
A is for non-linear instruments (not used here)B is the multiplierC is the offset
Offsets
Think of the range of the instrument• -50º C to +50º C• 223º Kelvin to 323º Kelvin• 0 ppm to 0.500 ppm
Then think: Where is the low end of the range in relation to 0?
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Offset examples
• A barometric pressure sensor has a range from 26 to 32 inches of mercury– This is an offset of +26
• An ozone analyzer senses ozone between 0 and 500 ppb– This is an offset of 0
More offset examplesWhere is the low end of the instrument range in relation to 0?
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0
0
Temperature ºC
-50 ºC +50 ºCRange = 100 ºCLow end of range = -50Offset = -50
Ozone
500 ppbRange = 500ppbLow end of range = 0Offset = 0
28” 32”Barometric Pressure
Rang = 4” of HgLow end of Range = 28”Offset = +28
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Contrasting Digital vs. Analog Connectivity
• In high sensitivity precursor gas applications, signal exists at bottom of usable voltage range and data stream may be affected by noise.
• D/A range may be limited to 10 bit (1024 steps) in some cases (TEI-C series).
• D/A calibrations may be required to “match” analyzer output to data logger input readings.
• Many instruments have limited analog-out capability, restricting availability of diagnostic data (e.g., R&P TEOM has only 3 analog outputs).
• Acquiring auxiliary data requires additional wiring creating opportunities for loose or broken physical connections.
Analog Connection
Analog: Established method using ranged line voltage across a connection to track a single data type.
Slide Courtesy of U.S. EPA Office of Air Quality Planning and Standards -Nealson Watkins & Lewis Weinstock
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Contrasting Digital vs. Analog Connectivity
• Multiple data types can stream across single connection.
• Nearly unlimited diagnostic retrieval capability.• No risk of data corruption due to analog noise
at very small voltage signal levels or due to ground loop effects.
• A/D calibrations not required.• Addressable monitors can be individually
interrogated and multi-dropped to reduce wiring.
• Additional flexibility in tracking over-range conditions where analog signal “pegs.”
• Digital systems sensitive to changes in instrument firmware and output formats!
Digital Connection
Digital: Uses connection such as RS-232 to track and log all available monitor information.
Slide Courtesy of U.S. EPA Office of Air Quality Planning and Standards -Nealson Watkins & Lewis Weinstock
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Envidas for Windows (EFW)• PC based system (no “logger” required).• 64 available channels for analog or
digital inputs.• Access via serial, digital I/O, analog I/O,
or other data loggers.• Standard configurations facilitate digital
connectivity with commercially available monitors.
• Real-time data, on the fly corrections, data validation, alarms, diagnostics.
• Multi-site, remote command and control capable (over TCP/IP).
• Easily configurable for internet-based polling via broad-band.
• Capability to emulate a data logger allows its insertion into existing data acquisition network.
Digital I/O & Relay Control
Slide Courtesy of U.S. EPA Office of Air Quality Planning and Standards -Nealson Watkins & Lewis Weinstock
AQS File for SO2
Tire chains – “Practical bag”