Teledyne HFM-301 User manual

HFM-301/305/306 Flow Meters
HFC-303/307 Flow Controllers
INSTRUCTION MANUAL
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Export, reexport or diversion contrary to U.S. law is prohibited.

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Manual Print History
The print history shown below lists the printing dates of all revisions created for this manual. The revision level
letter increases alphabetically as the manual undergoes subsequent updates. Each new revision includes a
revised copy of this print history page.
Revision G (Document Number 152-102002) ................................................................................................................................. October 2002
Revision H (Document Number 152-082005).................................................................................................................................. August 2005
Revision J (Document Number 152-042006)..................................................................................................................................... March 2006
Revision K (Document Number 152-062008) ........................................................................................................................................ June 2008
Revision L (Document Number 152-082008) .................................................................................................................................. August 2008
Revision M (Document Number 152-082009) ................................................................................................................................. August 2009
Revision N (Document Number 152-102009) ................................................................................................................................. October 2009
Revision P (Document Number 152-082010) ..................................................................................................................................... August 2010
Revision Q (Document Number 152-052012) .......................................................................................................................................... May 2012
Revision R (Document Number 152-072014) .......................................................................................................................................... July 2014
Revision S (Document Number 152-032015) ..................................................................................................................................... March 2015
Revision T (Document Number 152-072016) .......................................................................................................................................... July 2016
Revision U (Document Number 152-042017) ....................................................................................................................................... April 2017
Revision U (Document Number 152-042017) ................................................................................................................................. August 2022
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Description of Symbols and Messages used in this manual
WARNING: indicates a hazardous situation, which, if not avoided, could result in death or
serious injury. Do not proceed beyond a WARNING notice until the indicated conditions are
fully understood.
CAUTION: indicates a hazardous situation, which if not avoided, could result in minor or
moderate injury. Do not proceed beyond a CAUTION notice until the indicated conditions are
fully understood and met.
NOTICE: calls attention to a procedure or practice that if not correctly performed or adhered
to, could result in equipment damage, loss of data, or inaccurate data.
NOTE: is used for tips and other digressions.
Hastings Instruments reserves the right to change or modify the design of its equipment without any
obligation to provide notification of change or intent to change.

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Table of Contents
1. GENERAL INFORMATION ................................................................................................. 5
FEATURES .............................................................................................................. 6
SPECIFICATIONS ......................................................................................................... 7
OPTIONAL 4-20 MA CURRENT OUTPUT .................................................................................. 9
ACCESSORIES ......................................................................................................... 10
1.4.1. Power Supplies.............................................................................................. 10
1.4.2. Cables ........................................................................................................ 10
2. INSTALLATION AND SETUP ............................................................................................ 11
RECEIVING INSPECTION ................................................................................................ 11
POWER REQUIREMENTS................................................................................................ 11
OUTPUT SIGNAL ...................................................................................................... 11
MECHANICAL CONNECTIONS ........................................................................................... 12
2.4.1. Gas Quality (Filtering) ..................................................................................... 12
2.4.2. Mounting ..................................................................................................... 12
2.4.3. Plumbing ..................................................................................................... 12
ELECTRICAL CONNECTIONS ............................................................................................ 13
OPERATION ........................................................................................................... 15
2.6.1. Operating Conditions ...................................................................................... 15
2.6.2. Zero Check .................................................................................................. 15
2.6.3. High Pressure Operation .................................................................................. 15
2.6.4. Vertical Mounting .......................................................................................... 18
2.6.5. Gas Blending ................................................................................................ 18
RANGE CHANGING .................................................................... ERROR! BOOKMARK NOT DEFINED.
OUTPUT FILTER ....................................................................................................... 19
CONTROLLING OTHER PROCESS VARIABLES (EXTERNAL INPUT) ......................................................... 20
COMMAND INPUT ...................................................................................................... 20
VALVE OVERRIDE CONTROL ........................................................................................... 20
GAIN POTENTIOMETER ................................................................................................ 21
TEMPERATURE COEFFICIENTS .......................................................................................... 21
3. MAINTENANCE ........................................................................................................... 22
TROUBLESHOOTING ................................................................................................... 22
ADJUSTMENTS (CALIBRATION PROCEDURE) ............................................................................ 24
ENDCAP REMOVAL .................................................................................................... 24
PRINTED CIRCUIT BOARD REPLACEMENT ............................................................................... 25
SENSOR REPLACEMENT ................................................................................................ 25
4. GAS CONVERSION FACTORS ........................................................................................... 26
5. WARRANTY AND REPAIR ............................................................................................... 27

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WARRANTY REPAIR POLICY ............................................................................................ 27
RETURN POLICY ...................................................................................................... 27
6. DRAWINGS ................................................................................................................ 28
HFM-301 ............................................................................................................ 28
HFC-303 ............................................................................................................ 29
HFM-305 ............................................................................................................ 30
HFM-306 ............................................................................................................ 31
HFC-307 ............................................................................................................ 32

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1. General Information
The Hastings 300 series high range mass flow meters and controllers are designed to accurately measure and
control mass flow at ranges between 25 slm and 10,000 slm with an accuracy of better than ±1% Full Scale
(HFM-306 is 2% FS). Hastings mass flow instruments do not require any periodic maintenance under normal
operating conditions with clean gases. No damage will occur from the use of moderate overpressures or
overflows (~300 psig/2.07 MPa for HFM-306, ~500 psi/3.45 MPa for all other models). Instruments are normally
calibrated with the appropriate standard calibration gas (nitrogen) then a correction factor is used to adjust
the output for the intended gas. Calibrations for other gases, such as oxygen, helium, and argon, are available
upon special order.
NOTICE: The instruments described in this manual may be available with multiple pinouts.
Ensure that all electrical connections are correct.
NOTICE: The instruments described in this manual are designed for INDOOR and DRY use only.
NOTICE: The instruments described in this manual are designed for Class 2 installations in
accordance with IPC standards.
CAUTION: There are no operator serviceable parts or adjustments inside the product.
CAUTION: If this equipment is used in a manner other than that specified, the protection
provided by the equipment may be impaired.

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Features
LINEAR BY DESIGN. The HFM-301/305/306 and HFC-303/307 series are intrinsically linear (no linearization
circuitry is employed). Should field recalibration (a calibration standard is required) be desired, the customer
needs to simply set the zero and span points. There will be no appreciable linearity change of the instrument
when the flowing gas is changed.
NO FOLDOVER. The output signal is linear for very large overflows and is monotonically increasing thereafter.
The output signal will not come back on scale when flows an order of magnitude over the full-scale flow rate
are measured. This means no false acceptable readings during leak testing.
MODULAR SENSOR. The Hastings 300 series incorporates a removable/replaceable sensor module. Field
repairs to units can be achieved with a minimum of production line downtime. Replacing the sensor requires a
recalibration.
FAST SETTLING TIME. Changes in flow rate are detected in less than 250 milliseconds when using the standard
factory PC board settings.
FIELD RANGEABLE. The Hastings 300 series is available in ranges from 0-5 sccm to 0-25 slm. Each flow meter
has a shunt which can be quickly and easily exchanged in the field to select different ranges. Calibration,
however, is required.
CURRENT LOOP. The 4-20 mA option gives the user the advantages of a current loop output to minimize
environmental noise pickup.

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Specifications
WARNING: Do not operate instruments exceeding the specifications listed below. Failure to
heed this warning could result in serious personal injury and/or damage to the equipment.
Accuracy: HFM-301/305 & HFC-303/307: ±1% FS (±2% FS for HFM-306)
Repeatability: ±0.2% FS
Standard Pressure Rating: HFM-301, HFC-303: 500 psig [3.45 MPa]
with High Pressure Option of 1000 psig [6.89 MPa]
HFM-305, HFC-307: 500 psig [3.45 MPa]
HFM-306: 300 psig [2.07 MPa]
Pressure Coefficient: <0.016% of reading/psi (N2)
See pressure section for more information
Operating Temperature: -20 - 70°C in non-condensing environment
Temperature Coefficient (zero): Maximum ±0.12% FS/°C (-20-70°C)
Temperature Coefficient (span): Maximum ±0.08% Reading/°C (-20-70°C)
WARNING: Operation above 60 °C ambient may result in case temperatures capable of causing
burns.
Leak Integrity: < 1x10-9 sccs
Flow Ranges: 25 to 10,000 slm (N2 Equivalent)
Standard Output: 0-5 VDC (load min 2k Ω)
Optional Output: 4-20 mA (see load requirements in section 1.3)
Power Requirements: ±14-16 VDC @ 70 mA (meters absolute max)
±14-16 VDC @ 185 mA (controllers absolute max)
Class 2 power 150VA max fused
NOTICE: Use of an underpowered or under-voltage supply could result in equipment damage.
WARNING: Do not power with isolated drive circuits that are more than 36 volts above ground
potential or could reach 36 volts in the event of a fault. Failure to heed this warning could
result in serious personal injury and/or damage to the equipment.
Wetted Materials: Stainless Steel, Nickel, Viton,
Kalrez ® (Controller only)
Attitude Sensitivity of zero: <±1.4% FS for 90° without re-zeroing
(N2 @ 50 psig [446 KPa])

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Weight: HFM-301 = 3.5 lbs. [1.6 kg]
HFC-303 = 5.3 lbs. [2.4 kg]
HFM-305 = 8.1 lbs. [3.7 kg]
HFM-306 = 28.8 lbs. [13.1 kg]
HFC-301 = 15.2 lbs. [6.9 kg]
Electrical Connector: 15 pin subminiature “D”
Fitting Options: HFM-301/HFC-303: ½”, ¾” tube, 10, 12, 20 mm tube, 3/8”, ½” Male
NPT, ½” and ¾” VCR® and VCO®, ¾-16 and 1-1/16 MS straight female,
Surface Mount (301 small base only)
HFM-305/HFC-307: ¾”, 1” tube, 25 mm tube, ¾”, 1” Male NPT, 1”
Female NPT, 1” VCR® and VCO®, 1 5/16-12 SAE/MS Female thread
HFM-306: 1”, 1 ½”, 2” tube, 25 mm tube

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Optional 4-20 mA Current Output
An option to the standard 0-5 VDC output is the 4-20 mA current output that is proportional to flow. The 4-20
mA signal is produced from the 0-5 VDC output of the flow meter. The current loop output is useful for remote
applications where pickup noise could substantially affect the stability of the voltage output or long cable runs
where cable resistance would cause a voltage signal to decay.
The current loop signal replaces the voltage output on pin 6 of the DA-15 connector. The current loop is
sourced internally from the +15 VDC supply and must be returned to either the signal common (pin 5) or the
supply common (pin 9) after passing through the monitoring circuitry to complete the loop. If returning the
current to pin 5 (signal common), the load must be between 0 and 600 ohms. If returning current to pin 9
(supply common), the load must be between 600 and 1200 ohms. Failure to meet these conditions will cause
the current transmitter to fail.
The 4-20 mA I/O option can accept a current input for flow controllers. The 0-5 VDC command signal on pin 14
can be replaced by a 4 - 20mA command signal. The loop presets an impedance of 75 Ohms and is returned to
the power supply through the valve common.
Current Return Pin
Load Resistance
R Ω
5 (Signal Common)
0<R<600
9 (Negative Rail)
600<R<1200

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Accessories
1.4.1. Power Supplies
Hastings power supplies are available in one or four channel versions. They convert 100, 115 or 230VAC
to the ±15 VDC required to operate the instruments and provide a digital indication of the instrument
output. Hastings power supplies are power limited to no more than 150 VA max (fused). Interface
terminals for the analog output signals and a main power on/off switch are located on the rear panel as
well. For safety reasons it is recommended that the power supply (and on/off switch) be kept near the
flow instruments and that the on/off switch not be blocked. Throughout this manual, when reference is
made to a power supply, it is assumed the customer is using a Hastings power supply. Hastings Power
supplies change as new technology becomes available. For knowledge of the most up-to-date Hastings
power supplies, please consult either Hastings sales staff or our website at http://www.teledyne-hi.com
WARNING: To prevent the spread of fires in the event of a fault, only use power supplies power
limited to no more than 150 VA. The current available from a power supply used with a 300
Series instrument should be no greater than 1.6 A. Hastings power supplies meet these
requirements.
1.4.2. Cables
Cables to power Hastings flow instruments connect from the 15 pin "D" connector on the back of the
power supply directly to any of the 300 Series flow instruments. More information about the available
cables can be found on our website at http://www.teledyne-hi.com

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2. Installation and Setup
This section contains the necessary steps to install a new flow meter/controller into operation as quickly and
easily as possible. Please read the following thoroughly before attempting to install the instrument.
Receiving Inspection
Prior to opening, inspect for obvious signs of damage to the shipment. Immediately advise the carrier who
delivered the shipment if any damage is suspected. If the shipment has arrived intact, carefully unpack the
instrument and any accessories that have been ordered. Check each component shipped with the packing list.
Ensure that all parts are present (i.e., flowmeter, controller, power supply, cables, etc.). Optional equipment
or accessories will be listed separately on the packing list. There may also be one or more OPT (option) items
on the packing list. These normally refer to special ranges or special gas calibrations. They may also refer to
special helium leak tests, or high-pressure tests. In most cases, these are not separate parts, but special
options or modifications built into the flow instrument.
Quick Start
1. Ensure flow circuit mechanical connections are leak free
2. Ensure electrical connections are correct (see label).
3. Allow 30 min. to 1 hour for warm-up.
4. Note the flow signal decays toward zero.
5. Run ~20% flow through instrument for 5 minutes.
6. Insure zero flow; wait 2 minutes, then zero the instrument.
7. Instrument is ready for operation
Power Requirements
At their maximum power draws, the HFM-301/305/306/307 meters require ±15 VDC @ 70 mA, and the HFC-
303/307 controllers require ±15 VDC @ 185 mA (See specifications in sections 1.2). The HFM-300/HFC-302
Series supply voltages should be reasonably regulated as power supply ripple may propagate to the output (less
than 50 mV ripple is preferred). The supply voltage can vary from 14.0 to 16.0 VDC. Surge suppressors are
recommended to prevent power spikes reaching the instrument. The Hastings power supplies in section 1.4.1
are limited to no more than 150VA max and it satisfy all the recommended requirements. If using non-Hastings
power supplies with 300 Series instruments, it is strongly advised that they meet the recommendations in
section 1.4.1. The specs given earlier state the max assuming a 0.026” sensor and 4-20 mA output. In addition
to the specs reported in 1.2, the table below may be useful (the table assumes a 0.026” sensor):
Recommended Current Draws for 300 Series
Instruments
Instrument Type
\
Analog Output
0
-
5 V
4
-
20 mA
Meter
, ±14
-
16 VDC @
5
5
mA
70 mA
Controller
, ±14
-
16 VDC @
1
70
mA
185 mA
NOTICE: Use of an underpowered or under-voltage supply could result in equipment damage.
Output Signal
The standard output of the flow meter is a 0-5 VDC signal proportional to the flow rate. In Hastings power
supplies, the output is routed to the display and is also available at the terminals on the rear panel. If a
Hastings supply is not used, the output is available on pin 6 of the DA-15 connector and is referenced to pin 5.
It is recommended that the load resistance be no less than 2kΩ. If the optional 4-20 mA output is used, the
load impedance must be selected in accordance with Section 1.3.

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Mechanical Connections
2.4.1. Gas Quality (Filtering)
Impurities or foreign debris in the gas lines can have negative effects on device performance. The
smallest of the internal passageways in the HFM-300/HFC-302 Series is the diameter of the sensor tube,
which can be 0.026” (0.66 mm), 0.017” (0.43mm), or 0.014” (0.36mm), so the instrument requires
adequate filtering of the gas supply to prevent blockage or clogging of the tube.
2.4.2. Mounting
There are two mounting holes (#8-32 thread) in the bottom of the transducer that can be used to secure
it to a mounting bracket, if desired (HFM-306 has 4 mounting holes of ¼-28 size).
As explained in section 2.6.3 (High Pressure Operation), pressure can significantly affect readings and
accuracy. When mounting a flow instrument in anything other than a horizontal attitude, consideration
must be given to the fact that the heater coil can now set up a circulating flow through the sensor tube,
thereby throwing the zero off. This condition worsens with denser gases or with higher pressures.
Always check and match the direction of gas flow through the instrument and the arrow marked on the
flow instrument label. Whenever possible, install the instrument horizontally.
Always re-zero the instrument with zero flow, at its normal operating temperature and purged with its
intended gas at its normal operating pressure.
NOTICE: The flow instrument should be installed in a clean and careful manner. Take care not to
drop the product and avoid impacts to prevent damage.
WARNING: Make sure the work area is safe (de-pressurized) before installing a flow instrument.
Make sure emergency shutoff or pressure release valves are available for safe working
conditions. Do not exceed 500 psig unless the flowmeter is specifically rated for higher
pressures
2.4.3. Plumbing
The pressure regulator and the plumbing upstream must be of sufficient size to minimize changes in the
upstream pressure. When switching from full flow to zero flow, the inlet pressure of instrument should
rise to no more that 30% above the inlet pressure at full flow. In general, high-capacity regulators and
large internal diameter plumbing help make the system more stable. The pressure drop between the
regulator and the instrument due to line resistance should be minimized.
See the fitting options in the specifications section (1.2). Note the O-rings for the end cap are Viton
(optional Kalrez, Neoprene or Buna-N). It is suggested that all connections be leak-checked after
installation. This can be done by pressurizing the instrument (do not exceed pressure rating of the
instrument) and applying a diluted soap solution to the flow connections (bubbles would indicate leaks).

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Electrical Connections
If a power supply from Hastings Instruments is used, installation consists of connecting the 300 series cable
from the “D” connector on the rear of the power supply to the “D” connector on the top of the flow
meter/controller. The “H” pin-out requires cable AF-8-AM (grey molded back-shell). The “U” pin-out requires
cable # 65-791 (black molded back-shell).
If a different power supply is used, follow the instructions below when connecting the flow instrument and
refer to either table 2.1 or 2.2 for the applicable pin-out. Also see section 1.3 for the 4-20 mA connections.
The power supply used must be bipolar and capable of providing the appropriate current draws mentioned in
section 2.2. These voltages must be referenced to a common ground. One of the “common” pins must be
connected to the common terminal of the power supply. Case ground should be connected to the AC ground
locally. The cable shield (if available) should be connected to AC ground at the either the power supply end,
or the instrument end of the cable, not at both. Pin 6 is the output signal from the flow meter. The standard
output will be 0 to 5 VDC, where 5 VDC is 100% of the rated or full-scale flow.
The command (set point) input should be a 0-5 VDC signal (or 4-20mA if configured as such) and must be free of
spikes or other electrical noise, as these would generate false flow commands that the controller would
attempt to follow. The command signal should be referenced to signal common.
A valve override command is available to the flow controller. Connect the center pin of a single pole, three-
position switch (center off) to the override pin. Connect +15 VDC to one end of the three-position switch, and
-15 VDC to the other end. The valve will be forced full open when +15 VDC is supplied to the override pin, and
full closed when -15 VDC is applied. When there is no connection to the pin (the three-position switch is
centered) the valve will be in auto control and will obey the 0-5 VDC commands supplied to command (set-
point) input.
WARNING: Care must be taken to avoid any high voltages that may be present when dealing
with power supplies. Power supplies used with 300 Series instruments should be power limited
to no more than 150 VA max. The available current for each 300 Series instrument connected
to a power supply should not exceed 1.6 A.
WARNING: Care must be taken to avoid any high voltages that may be present when dealing
with power supplies.

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Figures 2.1/2.2, and Tables 2.1/2.2, show the 300/302 pin out.
Pin # Pin #
1 Signal Common 1 Do not use
2 Do not use 2 Do not use
3 Do not use 3 Do not use
4 +15 VDC 4 Do not use
5 5 Signal Common
6 Output 0-5 VDC (4-20mA) 6 Output 0-5 VDC (4-20mA)
7 Signal Common 7 Case Ground
8 Case Ground 8 Valve Override
9 Valve Override 9 -15VDC
10 10 Do not use
11 -15VDC 11 +15VDC
12 External Input 12 Signal Common
13 Signal Common 13 External Input
14 Signal Common 14 Set Point 0-5 VDC (4-20mA)
15 Set Point 0-5 VDC (4-20mA) 15 Do not use
Table 2.1
"U" Pin-Out
Table 2.2
"H" Pin-Out

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Operation
The standard instrument output signal is 0 - 5 VDC and is proportional to the flow (0 volts = zero flow, 5 Volts =
100% flow). The 4 - 20 mA option is also proportional to flow (4 mA = zero flow and 20 mA = 100% flow).
2.6.1. Operating Conditions
For proper operation, the combination of ambient temperature and gas temperature must be such that
the flow meter temperature remains between -20 and 70°C. The most accurate measurement of flow will
be obtained if the flow meter is zeroed at operating temperature as temperature shifts result in some
zero offset. Hastings 300 series instruments are intended for use in non-condensing environments only.
Condensate or any other liquids which enter the flow meter may destroy its electronic components.
2.6.2. Zero Check
Turn the power supply on if not already energized. Allow for a 1 hour
warm-up. Stop all flow through the instrument and wait 2 minutes.
Caution: Do not assume that all metering valves completely shut off
the flow. Even a slight leakage will cause an indication on the meter and
an apparent zero shift. For the standard 0 - 5 VDC output, adjust the
zero potentiometer located on the inlet side of the flowmeter until the
meter indicates zero. For the optional 4 - 20 mA output, adjust the zero
potentiometer so that the meter indicates 4 mA. This zero should be
checked periodically during normal operation. Zero adjustment is
required if there is a change in ambient temperature, or vertical
orientation of the flow meter/controller.
2.6.3. High Pressure Operation
Thermal mass flow meters measure the heat transfer caused by gas flow. This heat transfer is a function
of the constant pressure specific heat (Cp) of the gas. For monatomic gases the specific heat is
essentially a constant for all normal pressure/temperature conditions. As the gas structure becomes
more complex and as the molecular weight of the gas increases, the pressure inside of the sensing tube
increases and so does the specific heat of the gas. This is compensated somewhat by the effect of the
hoop strain of the tube wall caused by the internal pressure on the resistance heaters wrapped around
the sensing tube.
Larger tubing will have more strain than the smaller tubing and a larger associated pressure affect.
Charts of the effects of various gases on the span of the flow instruments as a function of pressure are
shown below for each of the available sensor diameters. The sensor tubing diameter is written on a label
mounted on the side of the sensor and is listed in the options in the order acknowledgement.

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If the system pressure is higher than 250 psig (1.7 MPa) the pressure induced error in the span reading
becomes significant. This error will approach 16% for nitrogen at 1000 psig. For accurate high-pressure
measurements this error must be corrected.
The formula for predicting the nitrogen mean error expressed as a fraction of the reading are:
Sensor Type
A
B
0.026”
-
2.2915*10
-
7
5.7198*10
-
5
0.017”
-
7.1066*10
-
8
5.2403*10
-
5
0.014”
-
5.3091*10
-
8
6.1278*10
-
5
𝐸𝑟𝑟𝑜𝑟 = 𝐴𝑃+𝐵𝑃
Where P is the pressure in psig and Error is the fraction of the reading in error.
The flow reading can be corrected as follows:
𝐶𝑜𝑟𝑟𝑒𝑐𝑡𝑒𝑑 = 𝐼𝑛𝑑𝑖𝑐𝑎𝑡𝑖𝑜𝑛 − (𝐼𝑛𝑑𝑖𝑐𝑎𝑡𝑖𝑜𝑛 × 𝐸𝑟𝑟𝑜𝑟)
Where the Indication is the indicated flow and Error is the result of the previous formula (or read from
charts above).

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2.6.4. Vertical Mounting
It is not recommended to mount the
instrument vertically if high pressure or high
density gas is being measured.
If the instrument is not mounted in a level
position and is operating at high pressure or
with high density gases, the increased gas
density will cause convection to flow through
the sensor tube. This natural convection flow
will be proportional to the square of the gas
density and therefore to system pressure. This
will be seen as a shift in the zero flow output
that changes as the system pressure changes.
Heavier gases will have more of an effect than
light gases.
If the error exceeds 20-30% (of full scale), the
zero circuit installed in the instruments may
no longer be able to be adjusted to
compensate for the error.
If the instrument is measuring light gases or low pressure, the change in the zero due to natural
convection will be minimal. Larger shifts could be zeroed out with the zero pot as long as the upstream
pressure is stable. A chart is shown here for nitrogen/air versus pressure.
CAUTION: The HFM-306 does not have a high pressure option and is only rated for a 300 psig
max working pressure.
2.6.5. Gas Blending
Gas blending is achieved by using the output of one flow controller as the control signal (setpoint or
scaled setpoint) to a second flow controller (maintaining a fixed ratio of one gas to another).
Multichannel Hastings Power Supplies allow users to configure this option, but other devices can be used,
provided they can scale and feed the output signal of one controller to another. The following formulas
are useful (Two controllers, unit A and unit B, where FS = Full Scale):
𝐴 𝐹𝑙𝑜𝑤 = (𝐴 𝐹𝑆 𝐹𝑙𝑜𝑤)𝐴 𝑂𝑢𝑡𝑝𝑢𝑡
𝐴 𝐹𝑆 𝑂𝑢𝑡𝑝𝑢𝑡, 𝑙𝑒𝑡 𝐵 𝑆𝑒𝑡𝑝𝑜𝑖𝑛𝑡 = 𝐴 𝑂𝑢𝑡𝑝𝑢𝑡 × 𝑆𝑐𝑎𝑙𝑒 𝐹𝑎𝑐𝑡𝑜𝑟
𝐵 𝐹𝑙𝑜𝑤 = (𝐵 𝐹𝑆 𝐹𝑙𝑜𝑤)𝐴 𝑂𝑢𝑡𝑝𝑢𝑡 × 𝑆𝑐𝑎𝑙𝑒 𝐹𝑎𝑐𝑡𝑜𝑟
𝐵 𝐹𝑆 𝑂𝑢𝑡𝑝𝑢𝑡 ,
𝐹𝑙𝑜𝑤 𝑅𝑎𝑡𝑖𝑜 = 𝐵 𝐹𝑙𝑜𝑤
𝐴 𝐹𝑙𝑜𝑤 =(𝑆𝑐𝑎𝑙𝑒 𝐹𝑎𝑐𝑡𝑜𝑟)(𝐵 𝐹𝑆 𝐹𝑙𝑜𝑤)(𝐴 𝐹𝑆 𝑂𝑢𝑡𝑝𝑢𝑡)
(𝐴 𝐹𝑆 𝐹𝑙𝑜𝑤)(𝐵 𝐹𝑆 𝑂𝑢𝑡𝑝𝑢𝑡)
𝑆𝑐𝑎𝑙𝑒 𝐹𝑎𝑐𝑡𝑜𝑟 = (𝐹𝑙𝑜𝑤 𝑅𝑎𝑡𝑖𝑜)(𝐴 𝐹𝑆 𝐹𝑙𝑜𝑤)(𝐵 𝐹𝑆 𝑂𝑢𝑡𝑝𝑢𝑡)
(𝐵 𝐹𝑆 𝐹𝑙𝑜𝑤)(𝐴 𝐹𝑆 𝑂𝑢𝑡𝑝𝑢𝑡)
In most cases the analog full scale output terms are the same so those two terms cancel out. The flow
ratio is usually known, so the only challenge is finding the value of the scale factor between the output
of A to generate the setpoint of B.
EXAMPLE: Controller A is a 100 SLM Nitrogen 5V controller. Controller B is a 10 SLM CO2 5V controller.
What needs to happen to maintain CO2 at 5% of the Nitrogen flow rate? See solution on following page.

301/303/305/306/307 Flowmeters and Controllers Instruction Manual
EAR99 Technology Subject to Restrictions Contained on the Cover Page Page 19 of 32
SOLUTION:
Use the formulas above:
𝐹𝑙𝑜𝑤 𝑅𝑎𝑡𝑖𝑜 = 5% = 0.05, 𝑆𝑐𝑎𝑙𝑒 𝐹𝑎𝑐𝑡𝑜𝑟 = (0.05)(100)(5)
(10)(5)= 0.5
Scale the output of controller A by 0.5 (half) and route the signal to the setpoint of controller B to flow
5% of controller A.
Output Filter
Occasionally noise from a user’s system is superimposed on
the output signal voltage. This noise may be due to high
turbulence in the flow stream (the sensor is fast enough to
measure this) or it could be electrical noise when the flow
instrument has a high internal gain (flow instruments with low
full-scale flows ~ 25 slm). Varying levels of radio frequency
noise or varying airflow over the electronics cover can also
induce noise.
Noise can be most pronounced when measuring the flow
output with a sampling analog/digital (A/D) converter. When
possible, program the system to take multiple samples and
average the readings to determine the flow rate.
If less noise is desired, install a jumper over the pins of JP1 on
the flow measurement card. See Figure above and right.
Covering the two bottom pins (2 & 3), will activate a resistor-
capacitor (RC) filter that has a time constant of 0.1 second.
This will increase the settling time of the indicated flow rate to approximately 0.4 seconds and remove
much of the noise. Covering the top two pins (1 & 2), will increase the filter time constant to 1
second. This will increase the settling time to approx. 4 seconds and remove most of the noise.
This adjustment will not affect the calibration of the flow meter circuit or the actual flow response to
change in command signal (flow controllers). This will only slow down the indicated response (output
voltage/current).

301/303/305/306/307 Flowmeters and Controllers Instruction Manual
EAR99 Technology Subject to Restrictions Contained on the Cover Page Page 20 of 32
Controlling Other Process Variables (External Input)
Flow controllers usually control mass flow. The control loop
opens and closes the valve to make the output flow signal
match the command signal. Occasionally, gas is added or
removed from a system to control some other process variable.
This could be system pressure, oxygen concentration, vacuum
level etc. If this process variable has a sensor that can supply
an analog signal proportional to its value, the flow controller
may be able to control this variable directly. This analog
output signal could be 0-5 volts, 0-10 volts (or 4-20 mA for units
with 4-20 mA boards) or any value in between.
On the controller card, JP4 sets whether the control loop
controls mass flow (5,6) or an external process variable (7,8).
See right. This process variable signal must be supplied on pin
13 of the D connector for H pinout units (pin 12 for U pinouts)
of the meter card. When the controller is set for external
input, it will open or close the valve as necessary to make the
external process variable signal match the command signal. If
the process variable has a response time that is much faster or
slower than the flow meter signal it may be necessary to adjust
the gain potentiometer (see section 2.11).
Command Input
The flow controller will operate normally with any command input signal between 0-5 volts (4-20 ma for
units with 4-20 ma input/output cards) If the command signal exceeds ±14 volts it may damage the
circuit cards. During normal operation the control loop will open or close the valve to bring the output
of the flow meter signal to within ± 0.001 volts of the command signal. The flow signal will not match
the command signal if there is insufficient gas pressure to generate the desired flow. If the command
signal exceeds 5 volts, the controller will continue to increase the flow until the output matches the
command signal. However, the flow output does not have any guaranteed accuracy values under these
conditions.
If the command signal is less than 2% of full scale (0.1 volts or 4.32 ma) the valve override control circuit
will activate in the closed position. This will force the valve completely closed regardless of the flow
signal.
Valve Override Control
The valve override control line provides a method to override the loop controller and open or close the
valve regardless of the flow or command signals. During normal operation this line must be allowed to
float freely. This will allow the loop control to open and close the valve as it requires. If the valve
override line is forced high (> +5 volts) the valve will be forced full open. If the valve-override line is
forced negative (< -5 volts) the valve will be forced closed.