Dwyer Omega – FMA6500 Series Mass Flow Controller w/RS485 Standard and Alarm Functions
Product Code: FMA6500
Manufacturer: Dwyer Omega
Microprocessor driven digital flow controllers allow one to program, record, and analyze flow rates of various gases with a computer via an RS485 interface (optional RS232 is available). Controllers can be programmed for various control functions including flow setpoint, totalizer, stop totaliser, read totaliser, totaliser from preset flow, stop at preset total, auto zero, and more.
Principles of Operation
Metered gases are divided into two laminar flow paths, one through the primary flow conduit, and the other through a capillary sensor tube. Both flow conduits are designed to ensure laminar flows and, therefore, the ratio of their flow rates is constant. Two precision temperature sensing windings on the sensor tube are heated, and when flow takes place, gas carries heat from the upstream to the downstream windings. The resultant temperature differential is proportional to the change in resistance of the sensor windings. A Wheatstone bridge design is used to monitor the temperature dependent resistance gradient on the sensor windings which is linearly proportional to the instantaneous rate of flow. The output of the Wheatstone bridge is converted to digital format with a 12 Bit ADC (analog to digital converter). An on-board microprocessor and nonvolatile memory store all calibration factors and directly control a proportional electromagnetic valve. The digital closed loop control system continuously compares the mass flow output with the selected flow rate. Deviations from the setpoint are corrected by compensating valve adjustments, with PID algorithm thus maintaining the desired flow parameters with a high degree of accuracy. Output signals of 0 to 5 Vdc or 4 to 20 mA are generated indicating mass molecular based flow rates of the metered gas.
Interface
The digital interface operates via RS485 (optional RS232) and provides access to applicable internal data including FLOW SETPOINT, ACTUAL FLOW, ZERO ADJUSTMENTS, and LINEARIZATION TABLE ADJUSTMENTS. The analog interface provides 0 to 5 Vdc, 0 to 10 Vdc and 4 to 20 mA inputs and outputs.
Auto Zero
The FMA6500 automatically nulls the sensor zero offset whenever the flow setpoint is below 2% of full scale. To accommodate this feature the control valve must fully close under that condition. Provisions are made to either disable, force or store the current auto zero via digital commands.
Totaliser
The firmware for the FMA6500 provides functions to register total gas quantity. The total mass of gas is calculated by integrating the actual gas flow rate with respect to time. Digital interface commands are provided to: SET the totalizer to ZERO; START /STOP totalizing the flow; READ the totalizer; START the totalizer at a preset flow STOP the flow at a preset total.
Multi-Gas Calibration
The FMA6500 is capable of storing primary calibration data for up to 10 gases. This feature allows the same FMA6500ST to be calibrated for multiple gases while maintaining the rated accuracy on each.
