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Dry Gas Meter (DGM) Calibration - US EPA Methods

This page contains the details of how to calibrate the Dry Gas Meter (DGM) used in the United States Environmental Protection Agency (US EPA) smokestack testing and isokinetic sampling Methods for stationary sources of air pollution.

DGMs are usually inside a Meter Console (Automatic or Manual). The sampled gas from the flue gas inside the smokestack goes into the DGM, and then to an Orifice Meter (or Orifice Tube). The Orifice Meter/Tube helps us know how to adjust the leak-free vacuum pump to increase or decrease the sampled gas velocity at the nozzle.

The gas volume measured by the DGM is very important, because it validates that the sample was collected isokinetically. 


List of reference smokestack testing methods:

  • US EPA Method 5 (Revision: December 7, 2020 version)
    • Download free PDF online here at the US EPA webpage on Method 5
    • Download free backup PDF copy from Aer Sampling here
  • US EPA Method 17
  • US EPA Method 23
  • US EPA Method 201
  • And many other methods based on US EPA Method 5
    • Download latest version of all US EPA Stack Testing Methods for free online at the US EPA Air Emission Measurement Center (EMC) general webpage here



Dry Gas Meter (DGM)

Dry Gas Meter (DGM) PN-119 Aer Sampling

Automatic Console (DGM is invisible) 

Manual Console with digital manometers (DGM is visible)

Manual Console with analog liquid manometers (DGM is visible)

Critical Orifices (Kit of five flowrates)

Reference Dry Gas Meter "Dry Test Meter"

Wet Test Meter (WTM) "Wet Gas Meter"

Bell Spirometer "Bell Prover"



What to calibrate

  • Dry Gas Meter (usually inside a Meter Console)


    Goal of calibration

    • To get the DGM Calibration Factor (Y), which is used to correct the reading of the DGM, and also to calculate the final isokinetic rate (US EPA Method 5, Section 12.11.1)
    • To get the Orifice Meter (Orifice Tube) Calibration Factor (ΔH@), which is used to check quickly that Y is still valid before the next calibration (US EPA Method 5, Section


      When is it required (calibration frequency)

      • After each field use (usually done on-site)
        • US EPA Method 5, Section 10.3.2
        • US EPA Method 17, Section 10
        • US EPA Method 23, Section 6
        • US EPA Method 201, Section 5.3.1
        • And many others


      How to calibrate?

      • Choose one of the below options:
        • Option A1: Critical Orifice at a single flowrate
          • Procedures: US EPA Method 5, Section 16.2
          • Easiest and most common option chosen because the Critical Orifice is light weight and the setup is minimal
          • Choose the Critical Orifice with a delta H (ΔH) value that is between the largest and smallest ΔH recorded during the sampling run). One Critical Orifice generates one flowrate (at a critical vacuum)
          • Only works if the Critical Orifice can operate at a "Critical Vacuum" of 0.472 of barometric pressure
          • At "critical vacuum", both the velocity and mass flowrate of the gas entering the Critical Orifice is constant at the velocity of sound
          • Critical Orifices themselves require calibration. Recommend to send for annual traceable calibration, because they are important calibration standards
        • Option A2: Reference Dry Gas Meter "Dry Test Meter"
          • Procedures: US EPA Method 5, Section 16.1
        • Option A3: Wet Test Meter (WTM) "Wet Gas Meter"
          • Procedures: US EPA Method 5, Section 10.3
        • Option A4: Bell Spirometer "Bell Prover"
          • Procedures: US EPA Method 5, Section 10.3


      Calibration Pass/Fail Criteria

      • For the DGM Calibration Factor (Y):
        • Individual Y value must be within 2% from the average Y
          • US EPA Method 5, Section 10.3.1 and Figure 5-5
        • Average Y value must be within 5% of the previous average Y
          • US EPA Method 5, Section 10.3.2 and 10.3.3
      • For the Orifice Meter (Orifice Tube) Calibration Factory (ΔH@):
        • Individual ΔH@ value must be within 0.2 inch (5.08 mmH2O) from the average ΔH@
          • US EPA Method 5, Section 10.3.1 and Figure 5-5


      Related topics: ISO/IEC 17025, ILAC MRA, scope of accreditation, traceability


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      In case of discrepancy between English version and the non-English version, the English version shall prevail.
      Doc ID: AERHQWW-page-cal-dgm-en
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