Omega Products FMA6502ST User Manual

GAS MASS FLOW CONTROLLERS

With RS485 Standard and Alarm Functions
For Clean Gases

FMA6500ST Series

Starts at

$

1495

Standard

⻬ Digital and Analog

Modes Operate
Simultaneously

⻬ Programmable Flow

Configurations

⻬ RS485 Standard,

Multi-Drop Capability
of Up to 256 units

⻬ Stores Calibration Data

for Up to 10 Gases

⻬ Totalizer Indicates

Total Gas Quantity

⻬ Alarm Limits for High

and Low Gas Flow

⻬ Conversion Factors

for Up to 256 Gases

⻬ Autotune Function

for Optimum
Control Response

⻬ Self Diagnostic Tests

FMA6502ST, $1495,
shown smaller than
actual size.

Microprocessor driven digital flow
controllers allow one to program,
record, and analyze flow rates of
various gases with a computer via
an RS485 interface (optional
RS232 is available).

Controllers can be programmed for
various control functions including,
flow setpoint, totalizer, stop
totalizer, read totalizer, totalizer
from preset flow, stop at preset
total, auto zero, and more.

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 flow, therefore, the
ratio of their flow rates remains
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. The output of the
Wheatstone bridge is converted to
digital format with a 12-Bit Adc
(analog to digital converter).

An on-board microprocessor and
nonvolatile memory store all
calibration factors and directly
control a proportional
electromagnetic valve. The digital
closed loop control system

D-XX

continuously compares the mass
flow output with the selected flow
rate. Deviations from the setpoint
are corrected by compensating valve
adjustments, with PID algorithm,
thus maintaining the desired flow
parameters with a high degree of
accuracy. Output signals of
0 to 5 Vdc or 4 to 20 mA are
generated indicating mass molecular
based flow rates of the metered gas.

Interface

The digital interface operates
via RS485 (optional RS232) and
provides access to applicable
internal data including: flow
setpoint, actual flow, zero
adjustments, and linearization table
adjustments. The analog interface
provides 0 to 5 Vdc, 0 to 10 Vdc
and 4 to 20 mA inputs and outputs.

Auto Zero

The FMA6500ST automatically nulls
the sensor zero offset whenever the
flow setpoint is below 2% FS. To
accommodate this feature the control
valve must fully close under that
condition. Provisions are made to
either disable, force, or store the
current auto zero via digital
commands.

Totalizer

The firmware for the FMA6500ST
provides functions to register total gas
quantity. The total mass of gas is
calculated by integrating the actual
gas flow rate with respect to time.
Digital interface commands are
provided to: set the totalizer to zero,
start/stop totalizing the flow, read the
totalizer, start the totalizer at a
preset flow, and stop the flow at a
preset total.

Multi-Gas Calibration Option

The FMA6500ST is capable of
storing primary calibration data for
up to 10 gases. This feature allows
the same FMA6500ST to be calibrated
for multiple gases while maintaining
the rated accuracy on each.

Standard 10-Point NIST Calibration

Optional up to 9 additional 10-point
calibration may be ordered at an
additional charge of $250 per gas.

Conversion Factors

Conversion factors for up to 256 gases
are stored in the FMA6500ST.
Conversion factors may be applied
to any of the ten gas calibrations via
digital interface commands.

Flow Alarms

High and Low gas flow ALARM limits
are programmed using the digital
interface. Alarm conditions are
reported via the digital interface or
can activate the contact closure
outputs.

Programmable Flow

OMEGA

®

software supports
programmable flow modes, allowing
execution of custom programming
of up to ten steps. Various flow
configurations include ramping,
linearized increasing, and
decreasing modes.

Autotune

The autotune function allows the
FMA6500ST to automatically
optimize control response for the
gas under actual process conditions.
During the autotune process, the
instrument adjusts PID gains for
optimum step response and

determine key control valve
characteristics (only available on
units with less than 80 L/min
maximum flow).

Contact Closure

Two sets of dry contact relay
outputs are provided to actuate
user supplied equipment. These are
programmable via the digital interface
such that the relays can be made to
switch when a specified event occurs
(e.g. when a low or high flow alarm
limit is exceeded or when the totalizer
reaches a specified value).

Valve Override

Means are provided to force the
control valve fully open (purge) or
fully closed via either the analog or
digital interfaces.

Self Diagnostics

Whenever power is first applied,
the FMA6500ST runs a series
of self diagnostic tests to
ensure that it is in optimum
working condition.

Engineering Units

The flow setpoint, measured gas
flow and associated totalizer data
is scaled directly in engineering
units via digital interface
commands. The following units of
measure are supported: % of FS,
mL/min, mL/hr, scfm, scfh, sL/min,
sL/hr, lbs/hr, lbs/min, and one user
defined unit of measure.

Leak Integrity

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

Balanced Power Supply

The FMA6500ST operates on
±15 Vdc. The current requirements
for the positive and negative power
supplies are balanced such that the
current in the power supply
common connection is minimized.
Maximum power consumption is

13.5 watts at ±15 Vdc.

SPECIFICATIONS

Accuracy (including linearity):

15 to 25°C (59 to 77°F) and 0.7 to 4 bar
(10 to 60 psia): ±1% of FS, 0 to 50°C
(32 to 122°F) and 0.3 to 10 bar (5 to
150 psia): ±2% of FS, ±1% of FS at a
specific temperature and pressure
with special calibration

Repeatability: ±0.15% FS
Turndown Ratio: 50:1
Response Time: 0.6 to 1.0 s to within

±2% of setpoint over 20% to 100% FS

Temperature Coefficient:

0.05% of full scale/°C or better

D-XX

FMA6502ST,
$1495, shown
smaller than
actual size.

Pressure Coefficient: 0.01% FS/psi

(0.07 bar) or better

Leak Integrity:

-9

1 x 10
the outside environment

Optimum Gas Pressure:

1.73 bar (25 psig)

Max Gas Pressure: 34.5 bar (500 psig)
Max Diff. Pressure: 3.4 bar (50 psig)

for up to 10 LPM, 2.8 bar (40 psig) for
15 LPM and greater

Gas and Ambient Temp:

5 to 50°C (41 to 122°F)
Output Signals: Linear 0 to 5 Vdc

(2000 Ω min load impedance);
0 to 10 Vdc (4000 Ω min impedance);
4 to 20 mA optional (0 to 500 Ω loop
resistance)

Communication Interface:

RS485, standard; RS232, optional

Transducer Input Power:

±15 Vdc, 450 mA maximum
Wetted Parts: 316 stainless steel,

416 stainless steel, FKM O-rings
Neoprene or Perfluoroelastomer
O-rings optional

Connections: Standard
compression fittings up to 30 LPM
models; for 60 LPM models and
greater:

Circuit Protection:

Circuit boards have built-in polarity
reversal protection; resettable fuses
provide power input protection

Calibration Options:

Standard 10-point NIST calibration
optional up to 9 additional 10-point
calibrations may be ordered for an
additional charge of $250 per gas

smL/sec Helium maximum to

1

⁄4"

3

⁄8" compression fittings

D