In this post, you will find the in-situ gas flowmeter calibration directions. The Sage method to verify that the thermal mass meter is still in calibration allows the meter to remain in the pipe, is easy and quick, and checks both the sensor and transmitter’s performance. If you are interested in comparing the Sage method to various other manufacturers’ onsite calibration methods, visit “Thermal Mass Flow Meter Manufacturers’ In-Situ Calibration Methods.”
Sage In-Situ Calibration Verification
The Sage Prime raw calibration milliwatts (mW), which is required to conduct an “in-situ” calibration check quickly and conveniently, is continuously shown on the top left-hand corner of the meter’s display. When comparing the raw mW data with the initially reported “no ﬂow” value, the meter’s calibration is verified. The initial data is on the data tag on the back of the meter (as well as on the Certificate of Conformance). When the two data points match, it verifies that the meter is calibrated, confirms that both the sensor and transmitter are accurate, that there is no drift or shift, and that the sensor is clean.
Create and verify that there is no gas flow. Any time the user creates a “no ﬂow” condition, they can perform the onsite calibration procedure. The user can accomplish this in a few ways. The obvious way is to close off the process gas flow. However, this is not always easy or possible, particularly in natural gas supply lines. Another inexpensive way to create a no-flow condition is to use one of the Sage Isolation Valve Assemblies (P/N SVA05 or SVA07). These assemblies are an affordable add-on for the Sage meter.
To do this:
- Loosen the lower collar clamp thoroughly using an Allen wrench (for the SVA05, use 9⁄64” and for the SVA07, 3⁄16”).
- Slightly loosen the compression ﬁtting until the probe can easily lift, then raise the meter’s probe until the safety chain becomes taut.
- Tighten the compression ﬁtting.
- Close the isolation valve and check the zero mW as per “2” below.
Alternatively, the user can perform an ambient air test to create a “no-flow” condition. In this case, merely remove the pipe’s probe and cover up the sensor with a plastic bag. Then place the capped probe into an empty plastic water bottle.
Compare the raw data mW display with initial factory data. Note the raw mW number on the top left-hand side of the meter’s display. After one to three minutes of “no ﬂow,” check the reading against the ﬂow meter’s data tag on the back of the meter. This data is also on the last line(s) of the meter’s Certificate of Conformance.
A value within five milliwatts (mW) of the original factory value (assuming the user checks the same gas at the same pressure) indicates that the meter is still in calibration.
A value between 5-10 mW of the initial factory value also means that the meter is still in calibration, but the reading may have been inﬂuenced by one or more of the following factors:
- gas composition
- non-zero conditions
- sensor orientation
If we investigate and correct these factors, one should expect that the difference between the “no-flow” mW display and the initial factory data would be less than or equal to 5 mW.
If the meter fails (or is borderline) the calibration verification, it is more likely that the sensor is dirty, and the next step would be to clean the sensor. A contaminated sensor could create additional heat transfer. One of the advantages of the Sage in-situ analysis is that it will not pass the calibration. In this case, remove the probe and clean the sensor (use a non-corrosive solvent). A soft brush may gently clean the sensor surface; however, use caution and avoid damaging the sensor elements (RTDs).
In any case, a technician in the field may be unable to simulate the initial Sage calibration conditions entirely while in the pipe. For this reason, a difference of 10 mW is acceptable and indicates the meter is still in calibration.
Why do we need In-Situ Calibration?
The Sage onsite calibration verification is a simple procedure that eliminates the need for annual factory calibrations and offers tremendous benefits to the user. This verification, of course, saves time and money for the user. To comply with some greenhouse gas or climate change regulations, Sage Metering recommends a quarterly in-situ calibration check for EPA 40CFR 98 and CDM Methodologies.
For CAR compliance, Sage Metering recommends a quarterly In-Situ Calibration Check for the following Protocols:
- U.S. Landﬁll Protocol, Version 4.0, Par. 6.2
- U.S. Livestock Protocol, Version 3.0, Par. 6.2
- U.S. Livestock Protocol, Version 4.0, Par. 6.3
- Mexico Landﬁll Protocol, Version 1.1, Par. 6.2
- Mexico Livestock Protocol, Version 2.0, Par. 6.2
As per the protocols, the maximum allowable drift is 5%. Calculate the drift by multiplying the mW change from factory value (see 2) by 1.0% (i.e., each mW change equals 1% drift).
Thermal Mass Flow Meters for Greenhouse Gas Monitoring – Part IV