The FC-2925 series of Mass Flow Controllers accurately and reliably measures and controls the mass flow rate of gases up to 1000 slm (2100 scfh) of Nitrogen equivalents. The FM- 3925 series of Mass Flow Meters operates over the same flow range and at pressures up to 500 psig.
The FC-2925 and FM-3925 are equipped with a card edge connector. The FC-2926 and FM-3926 are available with a 15-pin subminiature D connector and optional 4-20mA DC input and output signals, 0-SVDC is standard.
The FC-2925 Mass Flow Controller consists of a thermal gas flow sensor, bypass flow splitter, pilot-operated control valve and electronics. Tylan General developed thermal mass flow controllers over twenty years ago and is the worldwide leader today .

Accuracy
Tylan General’s thermal differential flow sensor provides highly accurate and repeatable mass measurement of gas flow. Because the sensor measures the mass flow of gas, it is independent of pressure and temperature changes. This ensures that flow are consistent in different systems or locations.

Thermal Gas Flow Sensor
The FC-2925 measures gas flow rates using Tylan General's patented temperature differential sensing device. The temperature difference of gas flowing past two heated, resistive temperature sensors is directly proportional to the mass flow rate of the gas. An insulated small diameter capillary is used in the sensing element which greatly reduces variations with attitude. This allows the FC-2925 and FM- 3925 to be mounted in any position

Bypass Flow Splitter
The bypass flow splitter smooths the primary gas flow into the laminar flow region and produces sufficient pressure drop to divert a small portion of gas into the thermal sensor. The flow range is factory set by adjusting the position and size of the stainless steel bypass.

Temperature Compensation
An added temperature compensating circuit improves the accuracy of the FC-2925 throughout the operating temperature range of the device. Effects due to ambient temperature fluctuations are reduced, and zero and span stability are greatly improved.

Pilot Operated Control Valve
The control mechanism in the flow controller uses a solenoid valve as a pilot to control a process gas-actuated bellows valve. The valve provides fast speed of response, is easily adjusted and has less than 5% shutoff capability. The bellows, constructed of 350 stainless steel, uses the process gas to open and close the control valve.

PID On-Board Control
On-board PIO control circuitry allows the FC-2925 to control the gas flow to a desired setpoint. A command setpoint of 0-5 VDC is sent to the FC-2925 which compares it to the flow reading and then drives the control valve up or down to achieve the desired flow .
The response to setpoint command is less than three seconds. A 0-5 VDC output signal is returned which indicates gas flow. Optional 4-20 mA DC current signals are available on the FC-2926 and FM-3926.

Autozero Circuit
Long-term repeatability is enhanced in the FC-2925 by a digital circuit which automatically resets the output to zero under no-flow conditions. This feature, standard in all FC- 2900 MFCs shifts the entire calibration curve to cancel many of the effects of temperature coefficient and calibration drift.