The ASAIR AS200B is a digital mass flow controller for clean, dry, non-corrosive gases. It combines measurement with an integrated control valve: the instrument measures the gas flow, compares it with the setpoint and adjusts the valve to maintain the requested flow. This is the practical difference between a mass flow controller and a device that only indicates flow.
AS200B and AS200L: keep the ranges separate
The AS200B configuration described here has a range of 0–50 SLM for nitrogen. The 100, 200 and 300 SLM ranges belong to the larger AS200L series. Specify the model, full-scale range, calibrated gas and reference conditions together; the series name alone does not define a usable configuration.
See the AS200B / AS200L equipment specification for a comparison of the two model families.
How the control loop works
- The automation system sends a flow setpoint.
- The MEMS thermal sensing element measures flow through the measuring channel.
- The electronics compare the measured value with the setpoint and command the integrated valve.
- The controller reports the measured flow through the configured RS-485 or analog interface.
Thermal measurement depends on the gas properties. A calibration for one gas must not be assumed to apply unchanged to another gas or mixture. Confirm the calibration gas and any conversion factor for the actual application.
AS200B selection data
The following values describe the AS200B source configuration. Confirm the ordered instrument, operating conditions and calibration documentation before using these values as acceptance criteria.
- Range: 0–50 SLM, nitrogen.
- Accuracy: ±1% of reading above 35% of full scale; ±0.35% of full scale below 35%.
- Linearity: ±0.5% of full scale.
- Repeatability: ±0.2% of full scale.
- Response time: 1 s.
- Maximum pressure: 0.45 MPa.
- Operating temperature: +5 to +45 °C.
- Supply: 15–28 V DC.
- Interfaces: RS-485, 1–5 V or 4–20 mA, depending on configuration.
- Mass: 0.95 kg.
Repeatability and absolute measurement accuracy are different specifications. The response of the complete installation also depends on the gas line volume and pressure dynamics; the controller's stated response time does not describe every installed process.
Gas, pressure and installation checks
SLM expresses mass flow as an equivalent volume flow at specified reference conditions. Use consistent reference temperature and pressure in the instrument specification, calibration certificate and process calculations.
Check the normal operating points as well as the full-scale value. The application needs a suitable minimum stable flow and enough valve control reserve. Confirm inlet pressure, outlet pressure and the required pressure differential. The differential must be sufficient for control without exceeding the pressure limits of the instrument or its connections.
Particles, condensate and corrosive components can change heat transfer or damage the measuring channel and valve. Define gas cleanliness and material compatibility before selecting the controller. Confirm the fitting type, mounting orientation, available space and pipe support against the actual instrument drawing.
Connecting the controller to automation
Confirm the selected interface, connector pinout, protocol documentation and analog scale. For a digital connection, define the device address and communication settings. The system design should also specify the required behavior on loss of communication or power and how flow faults are detected. These details belong in the application specification rather than being assumed from the availability of an RS-485 port.
Information needed for configuration and acceptance
- Gas or mixture composition, full-scale range and normal working points.
- Gas temperature, inlet and outlet pressures, and available pressure differential.
- Required accuracy, repeatability and response of the complete process.
- Wetted materials, cleanliness and leak-tightness requirements.
- Fittings, mounting orientation and installation dimensions.
- Power supply, interface, signal scale and required failure behavior.
- Calibration certificate, bench checks and acceptance report requirements.
For configuration review, provide these operating conditions with the required model and range. Current availability, commercial terms and project-specific compliance requirements must be confirmed for the destination and application.
Technical basis: LeakLab's Russian AS200B application article. This English version preserves the distinction between AS200B and AS200L and the stated conditions of the source data.