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Thermal Mass Flow Meters

A brief history and comparison

Thermal Technology and the Evolution of Mass Flow

Thermal mass flow controllers were originally developed in the 1960s and 1970s for the semiconductor industry for gas vapor deposition in semiconductor fabrication.

As time went on the thermal mass flow controller found it's way into other processes such as pharmaceutical drug discovery, leak testing and aerospace. Mass flow controller and mass flow meters are now used in any application that requires the precise control and measurement of process gasses.

Thermal technology is based on the principle of thermal convection. Thermal technology is based on anemometer technology that began in the early 1900s. The technology is longstanding and it works very well.

As the demand had risen for mass flow meters and mass flow controllers, so did the demand for expanded functionality in mass flow meters and mass flow controllers. Consumers required increased accuracy, increased speed of response, more features and easier operation. The expanding market for mass flow meters and mass flow controllers created new demands for existing thermal technology. Operating characteristics inherent to thermal technology such as long warm up times and slow response speed began to create opportunity for new technologies to fill the void inside the mass flow market. Inventors began finding new opportunity in the mass flow market and new technology slowly began to be introduced. Thus came the introduction of new style of devices such as coriolis and laminar, each having thier own new sets of strengths and weaknesses. Along with new technologies, thermal mass flow meters and mass flow controllers have continued to evolve.

Laminar vs Thermal

A side by side comparison

  

Alicat Mass Flow Devices

  		  

Typical Thermal Mass Flow Devices

  
 Sensor Solid-State Silicon Based Differential PressureRTD or Thermocouple
 Response Speed 10 milliseconds (no software corrections required)0.5-3.0 seconds (no software), 500 milliseconds (software corrections predict flow)
 Display Standard, IntegratedOptional if available, External Mount
 Totalizer Optional, IntegratedOptional if available, External Mount
 Process Data Integrated Display shows Mass Flow Rate, Volumetric Flow Rate, Line Temperature and Line Absolute Pressure Mass flow rate
 Output Options Standard integrated display, analog (either 0-5 Vdc, 0-10 Vdc, 1-5 Vdc, or 4-20mA), and Standard RS-232 (no special software required).
Optional 2nd analog output can be ordered to output either mass flow, volumetric flow, temperature, or absolute pressure.		Standard analog, optional display if available, optional digital output if available.
 Digital Output Standard output includes mass flow rate volumetric flow rate, line temperature, line absolute pressure, selected gas, AND total if ordered with totalizer option.Digital output of mass flow if available.
 Power 7-30 Vdc, 35mA. Standard AC/DC adapter jack AND cable connector pins. Can run off anything from a standard 9 Volt battery to 12 or 24 volt systems from supplies or an inexpensive wall plug adapter.Special supply with + and – regulated 15 Vdc
 Fittings Standard NPT or miniature pneumatic fittings. Inexpensive, adaptable to common components. Swage-lok® style fittings are also available upon request.Specialized Swage-lok®, VCR, etc.
 Multi-gas Versatility Standard 14 gas select menu from integrated display.Single gas, conversion charts
 Inherent Linearity YesNo
 Documentation Integrated display shows model number, serial number, date of manufacture, calibration technician, and software revision number. Model/Serial number label also standard.On paper included with unit, sticker
 Flow Ranges Ranges available from full scales of 0.5 standard cubic centimeters/min to full scales of 1500 standard liters/minRanges available from 10 standard cubic centimeters/min to 50 standard liters/min full scale.