Premium Analog Mass Flow Meter
For precise mass flow measurement of any clean dry gas including mixtures, toxics, corrosives, and combustible gases, consider our Model 830 MFM. The Model 830 is ideal for process monitoring, gas blending and flow calibration applications among many others.
Sierra’s Model 830 uses Sierra’s patented sensor design with access ports to facilitate easy sensor cleaning. In addition, Sierra’s Platinum Sensor Technology eliminates zero-drift and creates excellent long-term reliability.
- Accuracy of +/- 1% of full scale
- 316 stainless steel construction
- Flow ranges from 0-10 sccm to 0-500 slpm
- Direct monitoring of mass flow rate
- “Primary Standard” calibration for best accuracy & NIST traceability
- CE approved
The Series 800 Flow Sensing Principle
The operating principle of Sierra’s Side-Trak and Auto-Trak flow meters and controllers is based on heat transfer and the first law of thermodynamics. During operation process gas enters the instrument’s flow body and divides into two flow paths, one through the sensor tube, the other through the laminar flow element bypass. The laminar flow element bypass generates a pressure drop, P1–P2, forcing a small fraction of the total flow to pass through the sensor tube (m1) which is then monitored.
Two resistance temperature detector (RTD) coils around the sensor tube direct a constant amount of heat (H) into the gas stream. In actual operation, the gas mass flow carries heat from the upstream coil to the downstream coil. The resulting temperature difference (∆T) is detected by the RTD coils.
Figures 1-2 and 1-3 show the mass flow through the sensor tube as inversely proportional to the temperature difference of the coils. The coils are legs of a bridge circuit with an output voltage in direct proportion to the difference in the coils’ resistance; the result is the temperature difference (∆T). Two other parameters, heat input (H) and coefficient of specific heat (Cp) are both constant. The resulting output is nearly linear over the transducer’s normal operating range.
For mass flow controllers, once the gas flows through the monitoring section, it is then controlled by the built-in servo-control valve. For flows up to 500 slpm, Sierra’s proprietary high-efficiency FastTrak Electromagnetic Valve is used. The normally closed FastTrak valve is similar to an on/off solenoid valve, except that the current to the valve coil, and hence the magnetic field, is modulated so that the ferromagnetic valve armature, or valve plug, assumes the exact height above the valve’s orifice required to maintain the valve’s command flow. The result is nearly infinite resolution. All controllers with the Fast-Trak valves are available with a “Soft-Start” option for those processes that require it.
For higher flows of 50 to 200 scfm, controllers are equipped with Sierra’s microprocessor-controlled, motor-operated rotary valve. While the rotary valve does not provide a completely positive shut-off, it does offer accurate control for higher flow installations.