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Beta Attenuation Mass Monitors A Discussion of Technology. Dennis Hart Met One Instruments, Inc. Overview. History of beta gauge technology Theory of operation Beta gauge advantages Beta gauge safety BAM-1020 technical overview E-BAM technical overview What’s next in beta technology

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Beta attenuation mass monitors a discussion of technology

Beta Attenuation Mass MonitorsA Discussion of Technology

Dennis Hart

Met One Instruments, Inc.


  • History of beta gauge technology

  • Theory of operation

  • Beta gauge advantages

  • Beta gauge safety

  • BAM-1020 technical overview

  • E-BAM technical overview

  • What’s next in beta technology

  • Conclusion

History of beta technology
History of Beta Technology

  • 1930s - Beta attenuation measurement technology first developed for industrial processes.

  • 1970s - Beta attenuation adapted to measure particulate by Sibata Scientific of Japan.

  • 1990s - BAM-1020 developed with reduced size and advanced microprocessor control.

  • 2002 - E-BAM developed for rapid field deployment and variable data intervals.

History of beta technology1
History of Beta Technology

  • Over 2,000 BAM-1020 units deployed.

  • Over 200 E-BAM units deployed.

Theory of operation
Theory of Operation

  • Beta rays are measured through clean filter tape.

  • Air containing particulate is sampled and deposited on the filter tape.

  • Beta rays are measured through dirty filter tape.

  • The difference between the two measurements is proportional to the mass concentration.

Beta gauge advantages
Beta Gauge Advantages

  • Time proven, stable technology: beta gauges have been in use for over 60 years.

  • Beta attenuation technique is simple, easy to use, and requires less maintenance than other methods.

  • Fewer site trips required, ideal for remote deployment.

  • Met One beta gauges are manufactured and supported from the United States.

Beta gauge advantages1
Beta Gauge Advantages

  • Seasonal and geographical correction factors are not needed.

  • It is not necessary to calibrate the beta measurement system in the field.

  • BAMs provide excellent agreement with gravimetric reference standards when properly maintained and operated.

  • Beta technology is virtually unaffected by the chemical composition of the sampled particulate.

Beta gauge safety
Beta Gauge Safety

  • The BAM-1020 and E-BAM each contain a small amount of 14C, a naturally occurring radioactive isotope of carbon.

  • Activity level of the 60 mCi 14C source is similar to a commercial smoke detector, and is licensed with the NRC under the same provisions.

  • Sources with activity under 100 mCi require no special government licensing to own.

  • Met One Instruments has an “Exempt Distribution License” from the US-NRC to distribute the beta sources.

Beta gauge safety1
Beta Gauge Safety

  • Users are not required to take any specific precautions when handling the beta gauge.

  • USA customers do not require licensing to own a Met One beta gauge.

  • The end user will never need to remove, replace, or handle the beta source.

  • The unit may be returned to the factory for disposal at the end if its service life, although this is not required.

Bam 1020 advantages
BAM-1020 Advantages

  • Continuously samples and measures ambient air for particulate matter.

  • Designed to predict the mass concentration measured by manual gravimetric samplers with the highest accuracy.

  • Does not require the use of correction factors

Bam 1020 advantages1
BAM-1020 Advantages

  • 60 day continuous operation between filter tape changes.

  • Designed for long term operation at a fixed installation.

  • Powerful integrated 6 channel data logger compatible with a wide array of meteorological sensors.

  • Best accuracy of all beta models.

Us epa equivalent method
US-EPA Equivalent Method

  • Met One BAM-1020 is the ONLY US-EPA designated beta gauge currently manufactured.

  • EQPM-0798-122

  • Equivalency for PM10 measurement

Simplicity flow system
Simplicity – Flow System

  • The BAM-1020 airflow system consists of a few simple components:

    • Inlet/Nozzle

    • Temp/RH/BP sensors

    • Debris filter

    • Mass flow sensor

    • Flow controller

    • Pump (external)

Simplicity measurement system
Simplicity – Measurement System

  • The BAM-1020 measurement system consists of a few simple components:

    • Carbon 14 Beta source

    • Filter tape support

    • Photomultiplier tube detector

    • Preamp circuitry

Critical checks
Critical Checks

  • The flow system should be calibrated or verified on a regular basis.

  • A leak check is performed with every flow calibration.

  • The nozzle sealing surface and support vane may need to be cleaned more frequently in humid environments.

Critical checks1
Critical Checks

  • The nozzle seal against the filter tape is important for proper airflow regulation.

  • The nozzle and support vane need to be cleaned at least as often as the filter tape is changed.

Bam 1020 calibration
BAM-1020 Calibration

  • Calibration occurs once at the factory against a transfer standard in a smoke room chamber.

  • There are no environmental correction factors that need to be employed.

  • Zero and Span are checked once per hour during operation. No changes are made however.

E bam advantages
E-BAM Advantages

  • Rapid deployment, portable unit.

  • DC operation for batteries or solar arrays.

  • All weather construction.

  • Easy set up: may be mounted on tripod or existing structure.

  • Compatible with optional wind sensors for smoke tracking.

  • Instrument operating temperature between -30° and +40° C.

E bam advantages1
E-BAM Advantages

  • “As needed” filter tape advance. One roll of tape may last up to a year depending on concentration levels.

  • Real-time data capability due to simultaneous sampling and measurement.

  • Concentration can be calculated on a 5, 15, 30, or 60 minute basis. Higher time resolution than the BAM-1020 is possible.

  • Up to 200 days of data storage, depending on data storage rate.

E bam advantages2
E-BAM Advantages

  • Lower cost and less parts.

  • AirSys satellite communications available for remote data retrieval.

  • Replaceable integral air pump.

Mass calculation1
Mass Calculation


    • I0– beta measurement across clean filter

    • I – beta ray measurement across dirty filter

    •  – calibration coefficient (m2/g)

    • x – mass density on filter tape (g/m2)

    • A – dust spot deposition area on filter tape (m2 )

    • V – sampled volume (m3)

    • C – particulate matter concentration (g/m3)

How performance is measured
How Performance is Measured

  • Accuracy

    • Percentage deviation from 24-hour gravimetric Reference Standard

    • Beta technology has superior 24 hour accuracy compared to other methods.

  • Precision

    • Repeatability of a single measurement.

  • Stability

Measurement challenges
Measurement Challenges

  • Environmental conditions can play a role in the accuracy of beta attenuation measurements. The two main factors are:

    • Air temperature

    • Relative humidity and moisture.

Measurement challenges1
Measurement Challenges

  • Temperature:

    • The BAM-1020 must be in a temperature controlled environment.

    • The temperature of the air flow in the E-BAM is measured and automatically compensated.

Measurement challenges2
Measurement Challenges

  • Humidity:

    • Moisture accumulation on the sample spot may be measures as mass.

    • BAM-1020 and E-BAM use smart heater technology to lower the RH of incoming air.

    • Mild heat and hourly spot changes virtually preclude effects on VOCs.

    • Either unit may be operated at ambient conditions if desired.

What s next in beta technology
What’s Next in Beta Technology

  • Detector sensitivity and noise improvements.

  • New pump options for E-BAM.

  • Advances temperature correction algorithms.

  • Advanced filter tape materials.

    • Less affect on concentration measurement.

    • Tests ongoing to improve nozzle leaks with thinner material.

    • Studies underway for maximum concentration levels.


  • Met One Instruments is constantly testing and experimenting to improve the beta gauge product line.

  • BAM-1020 exhibits documented superior performance to other beta gauges.

  • We welcome suggestions for future improvements.


  • Applications/Sales: David Gobeli, Ph.D.

  • Science: Herbert Schloesser, Ph.D.

  • Service: Mike Putnam, Service Mgr.


  • (541) 471-7111