Thermal Flow Meter In-Situ Calibration Leader

Sage Metering has led the industry in introducing thermal mass flow meter in-situ calibration. In my earlier article, “Benefit of in-situ calibration for thermal flow meters,” I discussed the apparent advantages of being able to calibrate flow meters onsite. Specifically, an “in position” calibration saves time and money. By having a calibration check in the field, the meter does not have to be removed from service each year and returned to the manufacturer (or lab) for calibration. This post discusses Sage Metering’s approach to onsite calibration verification.

All Sage Meters can perform the In-Situ Calibration Check as long as a “no-flow” (0 SCFM) condition can be created. This check is quick and easy and doesn’t require a highly skilled technician to perform it. Additionally, other than an isolation valve assembly for the insertion-style meter to create a “no-flow” condition, this feature’s cost is built into the Sage Metering low price.

The Sage In-Situ calibration is truly a check. It not only verifies that the unit is accurate; it also indicates that the sensor is clean. If, for some reason, the meter does not pass the calibration check the first time, in most cases simply cleaning the sensor and re-testing will verify that the meter is accurate and hasn’t drifted or shifted.

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

While the meter is manufactured, the Sage Zeroing Chamber records 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 on the meter’s Certificate of Conformance.

To view how easy and quick the Sage Metering operation is, visit In-Situ calibration as easy as 1-2-3. As other manufacturers bring their in-situ calibration solutions to the market, it becomes clear that Sage is still leading the way. At first glimpse, the advantages of the Sage Metering approach over other thermal manufacturers with in-situ calibration capability are:

• Sage has no additional cost for this feature, while one company charges a $2,000 premium per meter for their in-situ method.
• The Sage approach is easy as 1-2-3 and fast, while one company requires multiple data points to verify accuracy.
• A leading thermal mass meter manufacturer also requires a highly skilled technician to verify the accuracy using a nitrogen tank and a pressure regulator, and a gauge kit at the meter site.
• If a Sage Sensor is dirty, the in-situ check will not pass, giving the technician a chance to clean the sensor. If the sensor is damaged, it will not pass either. In contrast, one company’s in-situ check cannot determine if the sensor is contaminated or damaged and will continue to provide inaccurate data.

Next, I’ll discuss one of the largest, if not the largest, thermal mass flow meter manufacturers’ approach to onsite verification in my next post.

Competitor Approach #1 – Expensive & Time Consuming

A leading thermal mass flowmeter manufacturer striving to contend with Sage Metering’s In-Situ Calibration Check recently introduced the option to purchase an in-situ calibration verification system for one of their models. It should be no surprise that other manufacturers are striving to offer alternatives to Sage’s award-winning flowmeter, which has set a new standard in gas mass measurement.

In “Leading the way for thermal flowmeter in-situ calibration,” I shared the Sage Metering approach to in-situ calibration. Here I explain how perhaps the largest gas mass flowmeter manufacturer is offering onsite calibrations too. A key difference between this manufacturer’s approach and Sage Metering is that they offer the option to buy the meter with a calibration verification system.  Like any option, an added expense is associated with it, and it carries a hefty price tag of about $2,000 per meter in addition to the meter cost.

The manufacturer provides a calibration certificate with data from various pressure points and recommends the customer to repeat the calibration check at the same points to establish a baseline.

Their patented process involves installing a plumbing module near the meter, including a check valve and sonic nozzle. To calibrate the thermal mass meter, a trained technician must loosen the locking collar and packing gland nut on the meter’s insertion probe, rotate it, and lift the probe from the pipeline.  Another module (pressure regulator and gauge kit) is set up near the meter to regulate a secondary gas source where a nitrogen bottle is connected. This module includes a pressure regulator and digital output.  The regulated nitrogen flows to the plumbing module near the meter, where the check valve is opened, and gas flows to the sensor.  After a couple of minutes, allowing the electronic readings to stabilize, values are taken from the digital readout. This process is repeated at various pressure points, which the factory used in their initial factory calibration. The data points should comply with the factory-provided calibration data, and if they do, the process has verified the unit is accurate.

From an operations perspective, it would appear that a highly skilled technician would be required to install the calibration verification plumbing module, and the regulator module and calibrate the meter using bottled nitrogen. Nevertheless, this company should be commended for this unique approach since it does validate on-site that the thermal mass flow meter is accurate. The downside of this approach is that it is time-consuming and expensive.

Next, I discuss another manufacturer’s in-situ validation attempt.

Competitor # 2 – Validation – Not Verification

In-situ Validation

A popular thermal mass flow meter manufacturer claims to have a feature that “validates the flow meter’s calibration accuracy by testing the functionality of the sensor and associated signal processing circuitry.” This manufacturer suggests that the operator can validate flow meter calibration while the meter is still in the pipe at operating conditions by simply pushing a button. The company claims that the operator will receive a pass or fail message in three to four minutes, and the data is stored in the meter.

While the meter is being “validated,” an integrated circuit within the meter regulates the sensor’s signal. Data is collected and compared to the original factory calibration records. If the data matches within a customary range of tolerance, the meter is apparently validated. A validation certification can even be produced if a software tool is used to activate the process.

While this company claims the meter’s accuracy is validated by testing the sensor functionality, the only thing verified is that the flow meter is working properly, not its accuracy. Without testing at a known flow point, there is no way to confirm if the meter is truly in calibration. In contrast, Sage uses “no flow” (0 SCFM) as a known, dependable and repeatable flow point – and with our digital circuitry, any known flow point, even 0 SCFM, is an indicator of the absolute calibration curve. The other drawback of this company’s method is that you cannot verify if the sensor is clean or dirty. When the sensor is dirty, the meter continues to measure flow producing inaccurate data, and the operator never knows.

In the Sage Metering In-Situ Calibration method, a “no flow” condition is easily created using an isolation valve assembly. If the sensor is dirty, the meter will not pass the calibration check. This gives the technician a chance to inspect and clean the sensor and recheck the calibration.

On another point, the Sage Metering thermal mass flowmeter is less expensive. In fact, when comparing Sage Prime with this model, the customer could save $825-$1,175 depending on which options are selected.

While this manufacturer’s attempt is certainly simpler than the last method I discussed, it is not a true calibration check and another indicator that Sage Metering still leads the way in in-situ calibration.