Principles of Operation:
Metered gases are divided into two laminar flow paths, one through the primary flow conduit, and the other through a capillary sensor tube. Both flow conduits are designed to ensure laminar flows and therefore the ratio of their flow rates is constant.  Two precision temperature sensing windings on the sensor tube are heated, and when flow takes place, gas carries heat from the upstream to the downstream windings.  The resultant temperature differential is proportional to the change in resistance of the sensor windings.  A Wheatstone bridge design is used to
monitor the temperature dependent resistance gradient on the sensor windings which is linearly proportional to the instantaneous rate of flow.  Output signals of 0 to 5Vdc and 4 to 20mA are generated indicating mass molecular based flow rates of the metered gas.  Flow rates are unaffected by temperature and pressure variations within stated limitations. 

General Description:
Compact, self contained GFM mass flow meters are designed to read flow rates of gases. The rugged design coupled with instrumentation grade accuracy provides versatile and economical means of flow control.  Aluminum or stainless steel models with readout options of either engineering units (standard) or 0 to 100 percent displays are available.  The mechanical layout of the design includes an LCD readout built into the top of the transducer. This readout module is tiltable over 90 degrees to provide optimal reading comfort. It is connected to the transducer by a standard modular plug, and is also readily removable for remote reading installations.

Transducers without LCD readout are offered for OEM applications.  GFM mass flow meters are available with flow ranges from 10 mL/min to 1000 sL/min N2. Gases are connected by means of 1/4” 3/8” 1/2” compression fittings and 3/4” FNPT fittings. Optional fittings are available.  These meters may be used as bench top units or mounted by means of screws in the base.  Transducer power supply ports are fuse and polarity protected. 

Leak Integrity 1 x 10-7 smL/sec of helium max to outside environment.

Design Features

• Rigid metallic construction
• Maximum pressure of 1000 psig (70 bars)
• Leak integrity 1 x 10-7 of helium
• NIST traceable certification
• Built-in tiltable LCD readout
• 0-5 Vdc and 4-20 mA signals
• Circuit protection
• Can be used as a portable device
• Engineering units or 0 to 100% displays
• Totalizer option.

ACCURACY (including linearity):
±1.5% of full scale, including linearity for gas temperatures of 59 FF to 77 FF (15 FC to 25 FC ) and pressures of 5 to 60 psia (0.4 to 4.1 bars). Optional ±1% of full scale (certified calibration accuracy) associated with a given set of temperature and pressure values.

REPEATABILITY:
±0.5% of full scale

RESPONSE TIME:
Generally 2 seconds to within ±2% of actual flow rate over 25 to 100% of full scale

TEMPERATURE COEFFICIENT:
0.15% of full scale / FC

PRESSURE COEFFICIENT:
0.01% of full scale / psi (0.07 bar)

MAXIMUM PRESSURE DROP:
See table 1

GAS and AMBIENT TEMP:
32 FF to 122 FF (5F to 50 FC)

OUTPUT SIGNALS:

Linear 0-5 Vdc. 1000 ohms min. load impedance and 4-20 mA 0-250 ohms loop resistance

TRANSDUCER INPUT POWER:
+12 Vdc; 200 mA of maximum. +24 Vdc optional

TIME CONSTANT:
800 ms

GAS PRESSURE:
1000 psig (70 bars) maximum GFM 17, 37, 47. 20 psig (1.4 bars) optimum 500 psig (34.5 bars) GFM 57, 67, 77. 20 psig (1.4 bars) optimum

** MATERIALS IN FLUID CONTACT:
a. Aluminum models GFM Series: anodized aluminum, 316 stainless steel, brass and Viton7 O-rings
b. Stainless Steel models GFM17S, 37S,47S, 57S, 67S and 77S: 316 stainless steel and Viton7 O-rings.
Optional O-rings: Buna, EPR and Kalrez7
ATTITUDE SENSITIVITY:
No greater than +15 degree rotation from horizontal to vertical; standard calibration is in horizontal position

CONNECTIONS:
GFM 17 and 37: 1/4” compression fittings. Optional: 1/4” VCR7, 1/8”or 3/8” compression fittings (GFM17)
GFM 47: 3/8” compression fittings
GFM 57: 3/8” compression fittings
GFM 67: 1/2” compression fittings
GFM 77: 3/4” FNPT fittings or 3/4” compression fittings (GFM 77)

LEAK INTEGRITY:
1 x 10-7 smL/sec of helium maximum to the outside environment

CE COMPLIANT: EN 55011 class 1, class B; EN50082-1**The selection of materials of construction, is the responsibility of the customer. The company accepts no liability.