MKS MKSINST IE1000A, Инструкция по эксплуатации

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Operation of the MFC with Gases other than Air Chapter One: General Information
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The controller accepts a setpoint signal, compares it to the measured flow rate, and generates an offset error
signal. The error signal is conditioned, using a model based control algorithm, to provide a drive signal to the
low power, solenoid operated, pilot proportional control valve so that it can reposition the valve and reduce
the offset error signal to zero.
The pilot proportional control valve is a specially constructed solenoid valve in which the armature (moving
valve mechanism) is suspended. The arrangement ensures that minimal friction is present and makes precise
control possible. In the normally closed control valve, the solenoid lifts the armature and plug assembly away
from the valve seat to regulate the gas flow rate.
The pilot proportional control valve controls the pressure differential across the diaphragm of the main flow
valve.
Note The MFC must have sufficient differential pressure from inlet to outlet to achieve the setpoint.
If the device does not reach setpoint for lack of differential pressure, either increasing the inlet
pressure or decreasing the outlet pressure may be necessary.
Note For optimal control performance, the user should specify the inlet pressure provided to the MFC
through the diagnostic user interface.
When the actual flow rate reading is less than the setpoint value, the MFC opens the pilot valve to increase
the amount of gas entering the system. As the valve opens, assuming adequate differential pressure across the
flow controller, gas enters the process, so the flow rate rises to meet the setpoint value.
When the actual flow rate reading is more than the setpoint value, the MFC closes the pilot valve to decrease
the amount of gas entering the system. As the valve closes, there is a reduced flow of gas entering the process,
so the flow rate decreases to meet the setpoint value.
The flow exits the instrument at the established rate of flow downstream of the main flow valve.
Real-time accurate flow control is provided through advanced digital algorithms. Enabling real-time control
of process gas flow, accuracy and repeatability are significantly improved over conventional PID based digital
MFC’s.
Operation of the MFC with Gases other than Air
The IE500A / IE1000A High Flow Rate Mass Flow Controller does not use gas correction factors (as many
other mass flow controllers do) to control process gases other than air. The use of gas correction factors can
cause accuracy errors when running non-linear gases through the device.
IE500A / IE1000A High Flow Rate Mass Flow Controller multi-gas, multi-range functionality is based on
thermodynamic principals and multi-component functions that have been developed to accurately calculate
the non-linear gas flow of non-calibration gases, with respect to the calibration gas. The current MKS library
of gases and functions is in excess of 120 in number and includes most gases in common use within the
process industries. For gases whose parameters that are not already stored on the MFC, please consult an
MKS applications engineer.
When a gas other than the calibration gas is selected by the user, the MFC automatically pulls up the correct
functions that calculate the flow of that gas with respect to the original calibration, allowing the MFC to
report the gas flow for the gas in use immediately and with better accuracy than has previously been available.
In comparison, the typical MFC uses Gas Correction factors for converting the calibration gas flow into the
flow of the gas being used. This may lead to inaccuracy in the flow reported to levels as high as 6-10% (of
FS) depending on the gas used.