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 todays 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 Companys 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