Design Features

• rigid metallic construction
• available flow ranges starting from 0 to 10 sccm up to 0 to 100 slpm
• maximum pressure of 500 psig (34.5 bars)
• 0-5 Vdc or 4-20 mA signals
• leak integrity 1 x 10^-9 smL/sec of helium
• accuracy of ±1% full scale
• totalizer option
• circuit protection

AFM mass flow meter

Model AFM mass flow meters are designed to indicate flow rates of gases.

Each of these units incorporates an advanced straight tube sensor in conjunction with flow passage elements constructed of stainless steel. LED readouts of command modules are supplied with 0 to 100 percent calibrations. Zero and span adjustments are conviently accessible from outside of the transmitters.

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 or 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.

AFM mass flow meters are designed to meter flow rates of gases, and are available with flow ranges from 10 sccm to 100 slpm [N2]. Gases are connected by means of 1/4”, 3/8”, or optional 1/8”compression fittings. These meters may be used as benchtop units or mounted by means of screws in the base.

Transducer power supply ports are fuse and polarity protected.

Leak Integrity
1 x 10^-9 smL/sec of helium max to outside environment.

Mass Flow Systems
Complete Mass Flow Systems include Command Modules, transducers and cables. Command modules contain appropriate power supplies, digital panel meters with 3-1/2“ digit LED readouts and high precision potentiometers. External RS-232 or RS-485 are optional. Analog outputs are accessible through convenient 9 pin D-connectors.

ACCURACY
: ±1% of full scale, including linearity for gas temperatures ranging from 59 FF to 77 FF (15 FC to 25 FC) and pressures of 10 to 60 psia (0.7 to 4.1 bars); ±2% of full scale including linearity ranging from 41 FF to 122 FF (5 FC to 50 FC) and pressures of 5 to 150 psia (0.35 to 10.3 bars).

REPEATABILITY:
±0.2% of full scale.

TIME CONSTANT:
AFM SERIES - 300 ms
AFC26 (Qmax = 10 sL/min): 300 ms
AFC36 (Qmax = 50 sL/min): 600 ms
AFC46 (Qmax = 100 sL/min): 600 ms

RESPONSE TIME:
AFM SERIES: Approximately 1 second to within ±2% of set flow rate for 25% to 100% of full scale flow.
AFC26 (Qmax = 10 sL/min): Approximately 1 second to within ±2% of set flow rate for 25% to 100% of full scale flow.
AFC36 (Qmax = 50 sL/min) and AFC46 (Qmax=100 sL/min): Approximately 2 second to within ±2% of set flow rate
for 25% to 100% of full scale flow.

TEMPERATURE COEFFICIENT:
0.1% of full scale/ FC.

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

OPTIMUM GAS PRESSURE:
25 psig (1.73 bars).

MAXIMUM GAS PRESSURE:
1000 psig (70 bars) maximum. Standard calibration is at 20 psig (1.4 bars) inlet pressure.

MAX. PRESSURE DROP:
[cm H2O] (at full scale flow)
Refer to Table 13.

GAS AND AMBIENT TEMPERATURE:
41 FF to 122 FF (5 FC to 50 FC).

LEAK INTEGRITY:
1 x 10-9 smL/sec of helium maximum, to the outside environment.

**MATERIALS IN FLUID CONTACT:
316 stainless steel, 416 stainless steel, 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.

OUTPUT SIGNALS:
Linear 0-5 Vdc (2000 W min. load impedance); 4 - 20 mA optional (0 - 500 Ω loop resistance); maximum noise 20 mV peak to peak.

CONNECTIONS:
AFM/AFC26, AFM/AFC36: 1/4” compression fittings.
AFM/AFC46: 3/8” compression fittings.
Optional: 1/8” or 3/8” compression fittings or 1/4” VCR7 fittings.

TRANSDUCER INPUT POWER:
AFM/AFC26: +15 ±5% Vdc, 80 mA max, 1.2W; -15 ± 5% Vdc, 200 mA max, 3W;
AFC36/AFC46: +15 ±5% Vdc, 220 mA max, 3.3W; -15 ±5% Vdc, 600 mA max, 9W.

CIRCUIT PROTECTION:
Circuit boards have built-in polarity reversal protection. Replaceable fuses provide power input protection.