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

43

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”