Thermal Mass Flow Meters for Greenhouse Gas Monitoring – Part IV

U.S. facilities emitting 25,000 metric tons of CO2e per year are required by EPA 40 CFR Part 98 Regulations to report greenhouse gas emissions. The new regulations create the need to monitor greenhouse gases, but the conditions associated with many emitters’ applications make measuring GHG challenging for most flow meters. Thermal flow meters perform well in many of these applications to comply with the strict EPA calibration requirements. This post discusses how the Sage Thermal Mass Flow Meter is the best choice for many greenhouse gas reporting applications because it fully complies with EPA calibration requirements.

SAGE has brought to market the first digitally-driven circuit design, which eliminates the traditional analog Wheatstone bridge. This feature provides SAGE products with the ability to:

1. Eliminate analog drift, which improves stability and long term reproducibility
2. Show a reproducible zero flow point, permitting reliable and straightforward calibration verification
3. Maintain higher resolution providing greater rangeability
4. Eliminate self-heating because of the digitally-driven temperature sensor
5. Match overheat to an application for greater signal resolution
6. Offer a remote style up to 1000’ from the probe, and lead-length compensated (since the junction box has no circuitry, it is suitable for harsh environments)
7. Ensure accurate flow measurement over a wide range of process temperatures due to improved temperature compensation

SAGE has brought to market the first graphical display in the thermal flow industry, which provides:

1. Flow rate, temperature, totalized flow, diagnostics, and a signal at a single glance
2. A high contrast graphic display that adjusts to ambient lighting, making it easy to read

EPA Calibration Requirements

Installation variances and the gas composition often impact flow meter performance. Most TMFM manufacturers require periodic recalibration to assure accuracy; in that case, the meter must be taken offline and returned to the factory (or a third party), which can be expensive and inconvenient.

The EPA greenhouse gas rule requires that the meters be checked frequently for calibration. The SAGE meter offers the convenience of efficiently verifying that the meter is accurate through the SAGE In-Situ Calibration. The SAGE product does not have to be removed. Calibration verification can be performed quickly and inexpensively in the pipe, which saves time and money from removing the meter and returning it for periodic re-calibration.

All SAGE meters can perform the in-situ calibration check as long as a “no-flow” (0 SCFM) condition is created. “No flow” is easily created using an isolation valve assembly with the insertion meter style. Unlike other TMFMs, the SAGE In-Situ Calibration not only verifies that the unit is accurate; it also indicates that the sensor is clean. If the meter does not pass the calibration check the first time, in most cases, merely cleaning the sensor and re-testing will verify that the meter is accurate and hasn’t drifted or shifted.

When the SAGE meter is manufactured, the SAGE Zeroing Chamber is used to record the “no flow” or 0 SCFM data point while subjecting the unit to the customer’s specified conditions (i.e., the gas or gas mix and pressure). This data point at “no flow” is one of many data points used for the flow meter’s NIST traceable calibration and is used as a convenient standard for the calibration check. This data point is conveniently recorded on the meter’s tag and the meter’s Certificate of Conformance.

Traditionally, TMFMs have relied upon the Wheatstone bridge, an electrical circuit used to measure resistance, but it is prone to drifting. One of the unique elements of SAGE’s approach is using a digital method of driving the sensors. The proprietary technology provides additional benefits, which include: improved signal stability, enhanced temperature compensation, better sensitivity to detect flow changes, improved resolution, and the capability of adjusting the meter’s operating range to match the customer’s specific operating conditions.

The EPA regulations (CFR 40 Part 98) require TMFMs to regularly be calibrated per manufacturer’s recommendations. Other TMFM manufacturers have recognized the benefit of an in-situ calibration verification, and a few manufacturers have developed their methods to verify calibration for their meters:

1. One manufacturer’s verification process requires the purchase of expensive add-on hardware. Read more.
2. Other manufacturers require the TMFM to be returned to the factory or a third party for recalibration, which is inconvenient and expensive, especially if the meter is out of the manufacturer’s country, which is typical for measuring carbon credits.
3. Another manufacturer’s process only verifies the electronics are operational and not that the meter is calibrated. Read more.

SAGE’s In-Situ Calibration verification process is straightforward, can be performed in the pipe quickly, and is inexpensive. The process verifies that the sensor and electronics are operational, eliminates the need for a factory recalibration, and meets all EPA regulations. Read more.

Sage Meter excels in many applications commonly associated with measuring greenhouse gases and is compliant with EPA strict calibration requirements. It may very well be the best choice for measuring GHG in many environmental applications.

To read the Sage Metering white paper in its entirety, visit “Greenhouse Gas Emissions Monitoring Using Thermal Mass Flow Meters.”