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GAS THERMAL MASS PRODUCTS

Thermal mass meters feature fast response, virtually zero maintenance, and precise measurement - all very important qualities among today's variety of applications.

McMillan Gas Thermal Mass products utilize this thermal sensing technology. Flow enters the unit, and a portion of the flow is redirected into a small tube. This tube has two coils, one downstream from the other. Each coil is heated, and, as the gas passes through the tube, the smart electronics sense the amount of heat transferred from one coil to the other. McMillan Company's patented* system insures that the zero remains stable and the sensor is extremely repeatable. The diagrams on the right illustrate both the principle of operation and a cutaway of a FLO-CONTROLLER (FLO-SENSORS AND METERS are very similar, but without integrated valve).

SENSING ELEMENT DIAGRAM



FLO-CONTROLLER CUTAWAY
If the product is a FLO-CONTROLLER, flow will then pass into the proportional solenoid valve. This valve is controlled by the active servo electronics, which compare a setpoint (either internal or provided by the customer) to the actual flow rate provided by the flow sensor and adjust the valve accordingly.

Q1 / Q2 = K1 / K2

Q1 is flow rate of new gas
Q2 is flow rate of calibration gas
K1 is K factor of new gas
K2 is K factor of calibration gas

Q1 = (K1 / K2) Q2


K FACTOR FORMULAS

The output of the thermal mass flow sensor is directly related to the specific heat characteristic of the gas being measured. Therefore, if a unit is calibrated for air, it is a relatively simple calculation to figure the calibration for nitrogen or some other similar gas. This advantage offers flexibility not found on many other types of flow sensors.

*US Patents 6,038,921 & 6,240,776. Other patents pending.