Thermal (Hot Wire) Design

Thermal mass flow sensors, meters, and controllers feature many benefits.  Fast response, virtually zero maintenance, and precise measurements are very important among today’s variety of applications.

The McMillan Company Model 50 & 80 Series 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 ensures the zero remains stable and the sensor is extremely repeatable. 

Figure 2: Sensing Coil on McMillan Thermal Sensors

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.

If you need to accurately measure or control a dry gas, the McMillan 50/80 Series may be the best choice for you.

*Patent #’s 6,119,730; 6,038,921; 6,240,776; GB2358930; GB234722; GB2370647. Other patents pending.