Teledyne Hastings Instruments Blog

Calibration is the cornerstone of measurement accuracy, ensuring that instruments deliver reliable and precise data. Thermal mass flow meters play a pivotal role in providing a dependable solution for various industries. The calibration of these instruments is a critical factor that demands meticulous attention. In this blog, we delve into the intricacies of thermal mass flow calibration, unraveling the science behind it and its significance in achieving accurate measurements.

 

The Basics: What is Thermal Mass Flow Meter Calibration?

Teledyne Hastings’s flow meters and flow controllers use thermal mass flow sensors. The Teledyne Hastings Instruments 200 Series thermal mass flow meters operate on the principle of heat transfer using thermocouple technology. The flow sensor consists of a capillary tube that is heated at the midpoint. Thermocouples are used to measure the temperature on both the inlet and outlet ends of the tube. As gas molecules travel through the flow sensor, heat is transferred downstream. The temperature differential between inlet and outlet correlates to the molecular flow rate of the gases. The molecular flow rate is directly proportional to the mass flow rate of the fluid. This relationship forms the basis for the calibration process, as accurate calibration ensures that the meter provides reliable measurements across a range of flow rates and conditions.

Calibration is indispensable for maintaining the accuracy and reliability of thermal mass flow meters. Over time, factors such as contamination, sensor degradation, environmental changes, or wear and tear can impact the meter's performance. Calibration allows for the correction of these deviations, ensuring that the meter consistently produces accurate readings. Moreover, many industries are subject to regulatory standards that mandate regular calibration to guarantee the reliability of the data collected.

 

How To Calibrate Your Mass Flow Meter

1. The first step in thermal mass flow calibration is establishing a reference standard. This is typically a device with a known and traceable accuracy. The reference standard is used to compare and verify the accuracy of the mass flow meter being calibrated. This can be a reference standard or another flow meter. A high accuracy 300 Vue thermal mass flow meter or mass flow controller with local touchscreen display would create a standard that the unit under calibration will match to.
   
   
2. Calibration involves subjecting the flow meter to controlled flow rates covering its entire operating range. The meter's response to these different flow conditions is carefully observed and compared to the reference standard. The best calibration would be used with actual gas to get the most accurate data points. Since the actual gas (e.g. Helium) could be expensive or rare, then a more accessible gas such as N2 or Air is used with a conversion factor to calculate the actual flow rate in the desired gas.
   
   
3. As the flow meter undergoes calibration, data on its performance at various flow rates is collected. This data is then analyzed to identify any deviations from the reference standard. The reference temperature and pressure may differ from the actual process temperature and pressure. Calibration software may be employed to streamline this process.
   
   
4.  If discrepancies are detected, adjustments are made to the thermal mass flow meter to correct its readings. This may involve recalibrating sensor elements or updating compensation factors. The goal is to align the meter's measurements with the reference standard. It is important to note how large these discrepancies are as it may require repair instead of calibration.

 

 

 

In the world of fluid dynamics and process control, selecting the appropriate flow measurement parameter is crucial for accurate and reliable data. Teledyne Hastings’s uses heat transfer technology to indirectly measure the molecular flow rate of dry gases. Our instruments can be used with volumetric flow units as they are converted to find the mass flow rate.

 

 

What is the Thermal Mass Flow Meter Working Principle?

Basic Design:

A mass flow meter consists of four basic components:

1. Electronic Circuit Board
2. Flow Sensor
3. Bypass Shunt
4. Base

*See Figure on right

 

In the world of fluid dynamics and process control, selecting the appropriate flow measurement parameter is crucial for accurate and reliable data. Teledyne Hastings’s uses heat transfer technology to indirectly measure the molecular flow rate of dry gases. Our instruments can be used with volumetric flow units as they are converted to find the mass flow rate.

 

 

 

 

 

 

 

 

 

There are numerous thermal mass flow sensor designs.  The Teledyne Hastings’ 200 Series sensor is shown in image on left.  This thermal mass flow sensor consists of a small 316SS capillary tube with a heater winding located in the center.  A thermocouple (TC-1) is located on the inlet side and another thermocouple (TC-2) is located on the outlet side.  At zero flow (no gas flow), the heat is transferred through the capillary tube in both directions towards the two thermocouples, each of which has the same temperature (see image on right, ZERO FLOW condition).  As gas flow moves through the capillary tube (inlet to outlet), heat is then transferred downstream by the gas molecules.  The temperature of TC-2 will increase, while the temperature of TC-1 will decrease.  This temperature differential correlates to the molecular flow rate of the gases (mass flow). 

 

Output:

A majority of thermal mass flow meters provide an analog output signal (0-5vdc, 4-20mA, etc.) that is directly proportional to the gas flow rate.  System integrators can directly acquire this signal for process control.  

If the installation is not configured for data acquisition, Teledyne Hastings offers convenient power supplies with integrated displays (see models THCD-101 and THCD-401 in image on right) and ready-to-use connector cables for quick start-up.

 

 

 

 

 

Some mass flow meters offer digital communication to convey the flow rate, while other models have a built-in color touchscreen display (See model HFC-D-302B Vue in image on left).​

 

 

 

 

 

 

Thermal Mass Flow Meter Advantages

Thermal mass flow meters have gained widespread popularity in various industries due to their numerous advantages in measuring the flow of gases. Let's explore some of the key advantages of thermal mass flow meters:

 

1. Direct Mass Flow Measurement:

One of the primary advantages of thermal mass flow meters is their ability to directly measure mass flow rate. Unlike other flow measurement methods that may require additional measurements or assumptions about fluid properties, thermal mass flow meters provide a direct and accurate measurement of gas flow.

2. Insensitive to Changes in Pressure and Temperature:

Thermal mass flow meters are less affected by variations in pressure and temperature compared to some other flow measurement technologies. This robustness allows for accurate measurements even in environments where these conditions may fluctuate, reducing the need for extensive compensation or correction factors.

3. Wide Range of Applicability:

Thermal mass flow meters can be used across a broad range of gas flow applications. They are suitable for measuring the flow of various gases, including compressed air, natural gas, and specialty gases. This versatility makes them valuable in industries such as pharmaceuticals, petrochemicals, automotive, aerospace, and more.

4. Low Pressure Drop:

Thermal mass flow meters typically have a low-pressure drop across the sensor, minimizing the impact on the system being measured.

 

As technology continues to advance, these instruments are likely to play an increasingly integral role in optimizing processes and improving overall efficiency.