Verifying Thermal Mass Flow Meter Calibration in the Field

When Magnetrol® sends a Thermatel® TA2 to a customer, the instrument is already pre-configured and calibrated for the specific application where it will be used. Whether the TA2 is being used to measure natural gas at an upstream oil and gas facility, nitrogen tank blanketing in a chemical plant or digester gas in a wastewater treatment plant, it arrives to the customer ready to use. However, many customers utilize these meters for regulatory purposes or for energy management projects, and want to verify reliability and performance in the field, most often on an annual basis. If the instrument has to be sent back to the manufacturer, recalibrations can cost tens of thousands of dollars and cause process downtime or loss of measurement. To meet these needs, MAGNETROL has developed a procedure to verify thermal mass flow meter calibration at the customer site with no external equipment necessary to purchase.

Verifying TA2 Calibration

In order to verify calibration, low flow and high flow conditions are simulated. This establishes baseline values that can be used for comparison at a later date. These baseline values are stored in the TA2 and located in the calibration certificate. All verification procedures should be conducted at room temperature.

A Thermatel® TA2 thermal mass flow meter

Low Flow Validation

To test low flow validation, the heater power is set and a temperature difference between the resistance temperature detectors (RTDs) is measured. In order to do this, first wrap the sensor tips of the TA2 to prevent air flow. On the TA2 display, select the diagnostic section and enter the Low Cal validate option. Once you enter, the test begins to run. In a short time, the temperature difference will stabilize and two temperatures will show on the display. One of the two is the original temperature difference between the sensors when the TA2 left the factory. The other is the new temperature difference that has just been measured. If the values are within 1.5 °C, the device is still within calibration. Some variance in temperature difference is given for variation of ambient temperatures as well as test methods. The user can store the value obtained (if it is different from the original value) and use it as the new baseline value or keep the original value that is reflected on the calibration certificate.

High Flow Validation

In order to test high flow validation, the TA2 must be placed vertically in a water bath. An easy way to do this is to hold the TA2 in place with a test stand and let the water settle. Select High Cal validate from the diagnostics section, just as you did with Low Cal validate for the low flow test. The heater power is once again set and the temperature difference is measured. These steps can be completed exactly as they were with the low flow validation to verify thermal mass flow meter calibration.

Both the low flow and high flow tests verify if the RTDs still measure the same amount of heat transfer in low and high flow conditions covering the entire calibration curve. Since thermal mass flow measurement is based on heat transfer, this is a true calibration test. All the features needed to test your TA2 are included at no extra charge and require no special equipment.

More Information 

For more information on the TA2 or to watch a video that demonstrates thermal mass flow meter calibration, visit flow.magnetrol.com.

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