Operating Principle of Brooks Thermal Mass Flowmeter:
The operating principle of the Brooks Mass Flow Controller is thermodynamic. A precision power supply directs heat to the midpoint of the sensor tube carrying the flow.
On the same tube equidistant upstream and downstream of the heat input, are resistance temperature measuring elements.
With no flow, the heat reaching each temperature element is equal. With increasing flow, the flowstream carries heat, away from the upstream element, T1 and an increasing, away from the upstream element, T1 and an increasing amount towards the downstream element T2.
An increasing temperature difference develops between the two elements and this difference is proportional to the amount of gas flowing or the mass flow rate.
A bridge circuit interprets the temperature difference and an amplifier provides the output to the control circuitry as well as a 0-5 Vdc output signal.
The control circuitry compares the command set-point to the flow signal and positions the precision solenoid control valve. When the command signal is below 1% of full scale, the control valve is positioned fully closed.
The control valve can be latched fully open or closed by activating the valve override circuit.
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