Brooks Instrument 5850i User Manual

Installation and Operation Manual

X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December, 2008

Model 5850i

Mass Flow Controller

Brooks® Model 5850i

Installation and Operation Manual

X-TMF-5850i-MFC-eng

Part Number: 541B108AAG

Brooks® Model 5850i

December, 2008

Essential Instructions

Read this page before proceeding!

Brooks Instrument designs, manufactures and tests its products to meet many national and international standards. Because
these instruments are sophisticated technical products, you must properly install, use and maintain them to ensure they
continue to operate within their normal specifications. The following instructions must be adhered to and integrated into your
safety program when installing, using and maintaining Brooks Products.

• Read all instructions prior to installing, operating and servicing the product. If this instruction manual is not the correct
manual, please see back cover for local sales office contact information. Save this instruction manual for future reference.

• If you do not understand any of the instructions, contact your Brooks Instrument representative for clarification.

• Follow all warnings, cautions and instructions marked on and supplied with the product.

• Inform and educate your personnel in the proper installation, operation and maintenance of the product.

• Install your equipment as specified in the installation instructions of the appropriate instruction manual and per applicable
local and national codes. Connect all products to the proper electrical and pressure sources.

• T o ensure proper performance, use qualified personnel to inst all, operate, update, program and maintain the product.

• When replacement parts are required, ensure that qualified people use replacement parts specified by Brooks Instrument.
Unauthorized parts and procedures can affect the product's performance and place the safe operation of your process at
risk. Look-alike substitutions may result in fire, electrical hazards or improper operation.

• Ensure that all equipment doors are closed and protective covers are in place, except when maintenance is being
performed by qualified persons, to prevent electrical shock and personal injury.

Pressure Equipment Directive (PED)

All pressure equipment with an internal pressure greater than 0.5 bar (g) and a size larger than 25mm or 1" (inch) falls under the
Pressure Equipment Directive (PED). The Directive is applicable within the European Economic Area (EU plus Norway, Iceland
and Liechtenstein). Pressure equipment can be traded freely within this area once the PED has been complied with.

• Section 1 of this manual contains important safety and operating instructions related to the PED directive.

• Meters described in this manual are in compliance with EN directive 97/23/EC module H Conformity Assessment.

• All Brooks Instrument Flowmeters fall under fluid group 1.

• Meters larger than 25mm or 1" (inch) are in compliance with category I, II, III of PED.

• Meters of 25mm or 1" (inch) or smaller are Sound Engineering Practice (SEP).

ESD (Electrostatic Discharge)

Handling Procedure:

1. Power to unit must be removed.

2. Personnel must be grounded, via a wrist strap or other safe, suitable means before any printed circuit card or other internal
device is installed, removed or adjusted.

3. Printed circuit cards must be transported in a conductive container . Boards must not be removed from protective enclosure
until immediately before installation. Removed boards must immediately be placed in protective container for transport,
storage or return to factory .

Comments

This instrument is not unique in its content of ESD (electrostatic discharge) sensitive components. Most modern electronic
designs contain components that utilize metal oxide technology (NMOS, SMOS, etc.). Experience has proven that even small
amounts of static electricity can damage or destroy these devices. Damaged components, even though they appear to function
properly, exhibit early failure.

Installation and Operation Manual

X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December, 2008

Dear Customer ,
We appreciate this opportunity to service your flow measurement and control requirements with a Brooks

Instrument device. Every day, flow customers all over the world turn to Brooks Instrument for solutions to their
gas and liquid low-flow applications. Brooks provides an array of flow measurement and control products for
various industries from biopharmaceuticals, oil and gas, fuel cell research and chemicals, to medical devices,
analytical instrumentation, semiconductor manufacturing, and more.

The Brooks product you have just received is of the highest quality available, offering superior performance,
reliability and value to the user. It is designed with the ever changing process conditions, accuracy requirements
and hostile process environments in mind to provide you with a lifetime of dependable service.

We recommend that you read this manual in its entirety. Should you require any additional information concerning
Brooks products and services, please contact your local Brooks Sales and Service Office listed on the back cover
of this manual or visit www.BrooksInstrument.com

Y ours sincerely ,
Brooks Instrument

Brooks® Model 5850i

Brooks® Model 5850i

Installation and Operation Manual

X-TMF-5850i-MFC-eng

Part Number: 541B108AAG

December, 2008

THIS PAGE WAS
INTENTIONALLY

LEFT BLANK

Installation and Operation Manual

X -TMF-5850i-MFC-eng
Part Number: 541B108AAG
December, 2008

Section 1
Introduction

Section 2
Installation

Contents

Brooks® Model 5850i

Paragraph Page
Number Number

1-1 Purpose ............................................................................. 1-1

1-2 Description ........................................................................ 1-1

1-3 Specifications .................................................................... 1-3

2-1 Receipt of Equipment........................................................ 2-1

2-2 Recommended S torage Practice ...................................... 2-1

2-3 Return Shipment ............................................................... 2-2

2-4 Gas Connections............................................................... 2-2

2-5 Installation ......................................................................... 2-3

2-6 In-Line Filter ...................................................................... 2-4

2-7 Electrical Interfacing.......................................................... 2-5

2-8 Configuring the PC Board ................................................. 2-8

Section 3
Operation

Section 4
Maintenance

Section 5
Parts List

3-1 Theory of Operation .......................................................... 3-1

3-2 Operating Procedure ......................................................... 3-2

3-3 Zero Adjustment ................................................................ 3-3

3-4 Calibration Procedure........................................................ 3-4

3-5 Response .......................................................................... 3-8

4-1 General ............................................................................. 4-1

4-2 Troubleshooting................................................................. 4-1

4-3 Sensor Tube...................................................................... 4-6

4-4 Disassembly and Assembly............................................... 4-6

4-5 Use of the Conversion Tables .......................................... 4-10

4-6 Use of Orifice Sizing Nomograph..................................... 4-11

4-7 Restrictor Sizing ............................................................... 4-15

5-1 General ............................................................................. 5-1

Section A
CE Certification

CE Certification of Mass Flow Equipment ......................... A-1

i

Contents

Brooks® Model 5850i

Figures

Installation and Operation Manual

X -TMF-5850i-MFC-eng

Part Number:541B108AAG

December, 2008

Figure Page

Number Number

1-1 Command Steps, Sof t Start Disabled................................ 1-2

1-2 0-100% Command S tep, Soft S t art Enabled ..................... 1-2

2-1 Model 5850i Dimensions ................................................... 2-3

2-2 "D" Type Connector Pin Arrangement ............................... 2-4

2-3 Maximum Allowable Loop Resistance ............................... 2-5

2-4 Common Electrical Hook-Ups ........................................... 2-6

2-5 Recommended I/O Wiring Configuration for Current Signals

(Non-Isolated Power Supply)............................................. 2-7

2-6 Recommended I/O Wiring Configuration for Current Signals

(Isolated Power Supply) .................................................... 2-8

3-1 Flow Sensor Operational Diagram .................................... 3-2

3-2 Flow Control System Block Diagram................................. 3-3

3-3 Model 5850i Calibration Connections................................ 3-6

3-4 Adjustment Potentiometer Location .................................. 3-6

3-5 PC Board Jumper Location & Function ............................. 3-7

3-6 Fast Response Adjustment ............................................... 3-9

4-1 Torque Sequence for the Valve Retainer Plate.................. 4-3

4-2a Valve Adjusting S p acer Locations(Normally Closed Valve N.C.)

.......................................................................................... 4-5

4-2b Valve Adjusting S p acer Locations(Normally Open Valve N.O.)

.......................................................................................... 4-6

4-3 V oltmeter Connections for V alve Adjustment .................... 4-8

4-4 Example Nomograph ....................................................... 4-18

5-1 Model 5850i Parts Drawing ............................................... 5-1

Tables

ii

Table Page

Number Number

2-1 Recommended Filter Size ................................................. 2-4

4-1 Bench Troubleshooting...................................................... 4-2

4-2 Sensor Troubleshooting .................................................... 4-4

4-3 Conversion Factors (Nitrogen Base) ................................ 4-12

4-4 Model 5850i Orifice Sizing Nomograph............................ 4-16

4-5 Model 5850i St andard Restrictors .................................... 4-19

5-1 Model 5850i Replacement Parts List................................. 5-2

5-2 Tool and S pare Part Kits for 5850i Series.......................... 5-3

Installation and Operation Manual

X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December, 2008

1-1 Purpose

Section 1 Introduction

Brooks® Model 5850i

The Brooks® Model 5850i Mass Flow Controller is a mass flow
measurement device designed for accurately measuring and rapidly
controlling flows of gases. This instruction manual is intended to provide
the user with all the information necessary to install, operate and maintain
the Brooks 5850i Mass Flow Controller. This manual is organized into five
sections:

Section 1 Introduction
Section 2 Installation
Section 3 Operation
Section 4 Maintenance
Section 5 Parts List

It is recommended that this manual be read in its entirety before attempting
to operate or repair the Model 5850i.

1-2 Description

The Brooks Model 5850i Mass Flow Controller is used widely in the
Semiconductor Industry as well as many others, where manual, electronic
or computer controlled gas handling occurs. The Model 5850i consists of
three basic units: a flow sensor , a control valve and an integral electronic
control system. This combination produces a stable gas flow , which
eliminates the need to continuously monitor and readjust gas pressures.
Standard features include:

Fast Response Control permits rapid gas settling times with little or no
over/undershoot. Refer to Figure 1-1.

Soft Start provides a flow ramping function which slows down the
introduction of the process gas for those processes which cannot tolerate
rapid flow transition. Refer to Section 2-7 and Figure 1-2.

Valve Override permits the user to fully open and close the control valve
independent of the setpoint (command) setting. Refer to Section 2-6.

Setpoint (Command) permits the user to program the mass flow controller
with an external 0-5 Vdc or 4-20 mAdc signal. Refer to Section 2-6.

Low Command Valve Inhibit (Auto Shutof f) prevent s the valve from
opening whenever the setpoint is less than 2% of full scale.

Removable Cleanable Sensor permits the user to clean or replace the
sensor. Refer to Section 4-4.

Output Limiting prevents possible damage to delicate data acquisition
devices by limiting the output to -0.7 Vdc and +6.8 Vdc on the voltage
signal output and 0 to 26 mA on the current output.

1-1

Section 1 Introduction

Brooks® Model 5850i

Installation and Operation Manual

X-TMF-5850i-MFC-eng

Part Number: 541B108AAG

December, 2008

Figure 1-1 Command Steps, Soft Start Disabled

Figure 1-2 0 - 100% Command Step, Soft Start Enabled

1-2

Installation and Operation Manual

X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December, 2008

1-3 Specifications

Section 1 Introduction

Brooks® Model 5850i

Standard Ranges

3 sccm to slpm* (nitrogen equivalent)

Accuracy

±1% full scale including linearity at calibrated conditions
±1.5% full scale including linearity for flow ranges greater than 20 slpm.

Repeatability

0.25% of rate

Response Time

Less than 6 seconds to within 2% of full scale final value with a 0 to 100%

command step.

Power Requirements

+15 to +28 Vdc — 245 mA @ +15 Vdc to 370 mA @ +28 Vdc

Ambient T emperature Limit s

Operating: 5 to 65°C (40 to 150°F)
Non-Operating: -25 to 100°C (-13 to +212°F)

Working Pressure

1500 psi (10.342 MPa) maximum

Allowable Differential Pressure

5 psi minimum, 50 psi maximum. Higher differential pressures are allow-

able depending on gas and range. Consult factory for details.

Output Signal

0-5 Vdc into 2,000 ohms or greater . Maximum ripple 3 mV.
Jumper selectable 4-20 mAdc or 0-20 mAdc.
Refer to Fig. 2-3 for maximum total loop resistance.

5 V olt Reference Output

5 Volt s ±0.2%. Maximum load 1k ohms.

1-3

Section 1 Introduction

Brooks® Model 5850i

Installation and Operation Manual

X-TMF-5850i-MFC-eng

Part Number: 541B108AAG

December, 2008

T emperature Sensitivity

Zero: Less than ±0.075% full scale per degree C.
Sp an: Less than ±1.0% full scale shif t over 10-50°C range.

Mounting Attitude Sensitivity

±0.5% maximum full scale deviation after re-zeroing.

Command Input

Jumper Selectable: 0-5 Vdc, Input resistance 200k ohm or 4-20 mAdc,

Input resistance 75 ohm.

Leak Integrity

1 x 10-9 Atm. scc/sec Helium

Control Range

50 to 1

Mechanical Connection

Interchangeable with most popular mass flow controllers.
Refer to Figur e 2 -1.

Electrical Connections

D-type, 15-pin connector (DA-15P). Mating connector supplied.

*Standard temperature and pressure in accordance with SEMI
(Semiconductor Equipment and Materials International) standard: 0°C and

101.3 kPa (760 Torr). The mass flow controller can be calibrated to other
reference standard conditions. Specify at time of ordering.

1-4

Installation and Operation Manual

X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December , 2008

2-1 Receipt of Equipment

Section 2 Installation

Brooks® Model 5850i

When the equipment is received, the outside packing case should be
checked for damage incurred during shipment. If the packing case is
damaged, the local carrier should be notified at once regarding his liability .
A report should be submitted to the Product Service Dep artment, Brooks
Instrument, Hatfield, Pennsylvania 19440-0903.

Remove the envelope containing the packing list. Carefully remove the
equipment from the packing case. Make sure spare parts are not
discarded with the packing materials. Inspect for damaged or missing
parts.

Brooks Instrument

407 W. V ine Street
P.O. Box 903
Hatfield, PA 19440 USA
Toll Free (888) 554-FLOW (3569)
Tel [phone]
Fax [phone]
E-m ail: BrooksAm @BrooksInstrument.com
www.BrooksInstrument.com

2-2 Recommended Storage Practice

Brooks Instrument Brooks Instrument

Neonstraat 3 1-4-4 Kitasuna Koto-Ku
6718 WX Ede, Netherlands Tokyo, 136-0073 Japan
P.O. Box 428 Tel [phone]
6710 BK Ede, Netherlands Fax [phone]
Tel [phone] Email: [e-mail]
Fax [phone]

E-mail: [e-mail]

If intermediate or long-term storage is required for equipment as supplied
by Brooks Instrument, it is recommended that said equipment be stored in
accordance with the following:

a. Within the original shipping container.
b. Store in a sheltered area with the following conditions:

1. Ambient temperature 21°C (70°F) nominal.

2. Relative humidity 45% nominal, 60% maximum/25% minimum.

Upon removal from storage, a visual inspection should be conducted
to verify its condi-tion is “as received.” If the equipment has been in
storage for an excess of ten (10) months or in conditions in excess
of those recommended, all pressure boundary seals should be
replaced and the device subjected to a pneumatic pressure test in
accordance with applicable vessel codes.

2-1

Section 2 Installation

Brooks® Model 5850i

2-3 Return Shipment

Installation and Operation Manual

X-TMF-5850i-MFC-eng

Part Number: 541B108AAG

December, 2008

Prior to returning any Brooks equipment to the factory , cont act the factory ­for a Return Materials Authorization Number (RMA#). This can be obt ained
at Brooks Instrument, Product Service Department, 407 West Vine Street,
Hatfield, P A 19440-0903, or call toll free 1-888-554-FLOW (3569).

Brooks Instrument

407 W. V ine Street
P.O. Box 903
Hatfield, PA 19440 USA
Toll Free (888) 554-FLOW (3569)
Tel [phone]
Fax [phone]
E-m ail: BrooksAm @BrooksInstrument.com
www.BrooksInstrument.com

Brooks Instrument Brooks Instrument

Neonstraat 3 1-4-4 Kitasuna Koto-Ku
6718 WX Ede, Netherlands Tokyo, 136-0073 Japan
P.O. Box 428 Tel [phone]
6710 BK Ede, Netherlands Fax [phone]
Tel [phone] Email: [e-mail]
Fax [phone]

E-mail: [e-mail]

2-4 Gas Connections

Also, completion of Form RPR003-1, Brooks Instrument Decontamination
Statement, as well as, a Material Safety Data Sheet (MSDS) for the fluid(s)
used in the meter, is required before any Brooks Personnel can begin
processing the equipment. Copies of the form can be obtained at one of
the locations above.

Standard inlet and outlet connections supplied on the Model 5850i are 1/4"
compression fittings.

Optional 1/8" compression, VCOTM and VCRTM connections are available
upon request. Prior to installation, make certain all piping is clean and free
of obstructions. Install the piping in such a manner that permits easy
removal if the instrument is to be removed for cleaning or test bench
troubleshooting.

2-2

Installation and Operation Manual

X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December , 2008

Connection "X" Dim.

1/8" Compression

Fitting 122.9

1/4" Compression

Fitting 127.5

1/4" Tube VCO

1/4" Tube VCR

3/8" Compression

Fitting 130.5

4.84

5.02

4.56

115.8

4.88

124.0

5.14

Section 2 Installation

Brooks® Model 5850i

Figure 2-1 Model 5850i Dimensions

2-5 Installation (Refer to Figures 2-1 through 2-4)

Recommended installation procedures:

a. The Model 5850i should be located in a clean dry atmosphere

relatively free from shock and vibration.
b. Leave sufficient room for access to the electrical components.
c. Install in such a manner that permits easy removal if the instrument

requires cleaning.

d. The Model 5850i Mass Flow Controller can be installed in any

position. However, mounting orient ations other than the original

factory calibration (see data sheet) will result in a ±0.5% maximum

full scale shift after re-zeroing.
e. When installing controllers with full scale flow rates of 10 slpm or

greater, be aware that sharp abrupt angles in the system piping

directly upstream of the controller may cause a small shift in accu-

racy. If possible, have at least ten pipe diameters of straight tubing

upstream of the 5850i MFC.

2-3

Section 2 Installation

Brooks® Model 5850i

Installation and Operation Manual

X-TMF-5850i-MFC-eng

Part Number: 541B108AAG

December, 2008

1 SETPOINT RETURN 9 SUPPLY COMMON

2 VOLTAGE SIGNAL OUTPUT 10 SIGNAL OUTPUT RETURN

3 NOT USED 11 5V REFERENCE OUTPUT

4 CURRENT SIGNAL OUTPUT 12 VALVE OVERRIDE INPUT

5 +15 TO +28 Vdc SUPPLY 13 NOT USED

6 NOT USED 14 CHASSIS GROUND

7 CURRENT SETPOINT INPUT 15 NOT USED

8 VOLTAGE SETPOINT INPUT

*JUMPER SELECTABLE

2-6 In-Line Filter

NOTE: Cable shield tied to chassis ground in connector. Make no
connection on customer end.

Figure 2-2 "D" Type Connector Pin Arrangement

Note: The control valve in the Model 5850i provides precision control and
is not designed for positive shut-off. If positive shut-off is required, it is
recommended that a separate shut-off valve be installed in-line.

It is recommended that an in-line filter be installed upstream from the
controller to prevent the possibility of any foreign material entering the flow
sensor or control valve. The filtering element should be replaced
periodically or ultrasonically cleaned.

2-4

Table 2-1 Recommended Filter Size

Maximum Flow Rate Recommended Filter Size

100 sccm 1 micron
500 sccm 2 microns

1 to 5 slpm 7 microns

10 to 30 slpm

15 microns

Installation and Operation Manual

X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December , 2008

Section 2 Installation

Brooks® Model 5850i

Figure 2-3 Maximum Allowable Loop Resistance

2-7 Electrical Interfacing

To insure proper operation, the 5850i must be connected per Figures 2-2,
2-3 and 2-4 and configured according to Section 2-7. As a minimum, the
following connections must be made for new installations:

Function

Chassis Ground
Signal Output Return
Volt age or Current Signal Output

22.5-28 Vdc Supply
Supply Common
Voltage or Current Setpoint Input
Setpoint Return

Electrical Hook-up
Setpoint (Command) Input

The 5850i Mass Flow Controller can be used with a current (4-20 mAdc)
or voltage (0-5 Vdc) setpoint. To use the current setpoint, connect the
setpoint (+) signal to pin 7 and the setpoint return (-) signal to pin 1 of the
D-connector and configure the PC Board per Section 2-7. To use the
voltage setpoint, connect the setpoint signal to pin 8 and the voltage
setpoint return to pin 1 of the D-connector and configure the PC Board per
Section 2-7.

(The Brook’s MFC acts as a current sink to a setpoint input signal.
The 0/4-20 mA setpoint signal should be “driven” into the MFC input by a
controlled current source. Reference Brook’s device specifications for the
setpoint input impedance.)

2-5

Section 2 Installation

Brooks® Model 5850i

Installation and Operation Manual

X-TMF-5850i-MFC-eng

Part Number: 541B108AAG

December, 2008

Signal Output

The flow signal output can be measured as a voltage and a current
simultaneously on two different pins of the D-connector. Pin 2 indicates the
flowrate with a 0-5 Vdc signal proportional to the mass flow rate. Pin 4
indicates the flowrate with either a 0-20 mAdc or 4-20 mAdc current signal
as determined by jumpers on the pc board (refer to Section 2-7 for jumper
positions). Both the current and voltage signals are returned on pin 10 of
the D-connector .

(The Brook’s MFC acts as the current source when providing a 0/4-20 mA
output signal to the load. The output signal is “driven” by the MFC into the
customer load. Reference Brook’s device specifications for maximum load
capacity.)

Supply

The power for the mass flow controller is connected to pin 5 (+22.5 to +28
Vdc) and pin 9 (supply common) of the D-connector . Refer to Section 1-3
for the power requirements.

NOTE: The length of wire for the power supply connections (pins 5 & 9)
must be kept as short as possible to insure the minimum voltage (+15) is
available at the mass flow controller .

Figure 2-4 Common Electrical Hook-Ups, Voltage I/O version

2-6

Installation and Operation Manual

X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December , 2008

Section 2 Installation

Brooks® Model 5850i

Chassis Ground

Connect earth ground to pin 14 of the D-connector .

V alve Override (connection optional)
The valve override function allows full opening and closing of the valve

independent of the setpoint:

To open the valve, apply +15 to +28 Vdc to pin 12
To close the valve, connect pin 12 to ground.
Isolating pin 12 (no connection) returns the

controller to normal operation.

NOTE: For normal operation, pin 12 must be left open (floating).

Figure 2-5 Recommended I/O Wiring Configuration for Current Signals (Non-Isolated Power Supply)

2-7

Section 2 Installation

Brooks® Model 5850i

Installation and Operation Manual

X-TMF-5850i-MFC-eng

Part Number: 541B108AAG

December, 2008

Figure 2-6 Recommended I/O Wiring Configuration for Current Signals (Isolated Power Supply)

2-8 Configuring the PC Board

NOTE: To obtain access to the jumpers, the electronics cover can must be
removed. Disconnect the power to the mass flow controller and any cables
to the D-connector and the valve coil connector. Remove the three screws at
the base of the can and remove the top jack post of the D-connector.
Remove the can. The can must be replaced before returning the unit to
service. Refer to Section 2-6 for the proper electrical hook-up. Refer to Figure
3-5 for pc board jumper locations and functions.

Setpoint (Command) Input

The mass flow controller can be configured for voltage or current setpoint
(command) input. Jumper J7 (green) must be in the right-hand position for
0-5 Vdc setpoint and in the left-hand position for a 4-20 mAdc setpoint
input.

Signal Output

A 0-5 Vdc flow signal output is always available. The current signal output
is jumper selectable for either 0-20 mAdc or 4-20 mAdc. Jumpers J3 and
J4 (blue) must be in the upper position for 0-20 mAdc output and in the
lower position for 4-20 mAdc output.

2-8

NOTE: Both J3 and J4 must be in the same position. Jumpers J3 and J4
do not affect the voltage output.

Soft Start

To enable soft start, place Jumper J2 (red) in the right-hand position (SS).
To disable soft start, place jumper J2 in the left-hand position (N).

Installation and Operation Manual

X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December , 2008

3-1 Theory of Operation

Section 3 Operation

Brooks® Model 5850i

The thermal mass flow sensing technique used in the 5850i works as
follows:

A precision power supply provides a constant power heat input (P) at the
heater which is located at the midpoint of the sensor tube. (Refer to Figure
3-1) At zero or no flow conditions, the heat reaching each temperature
sensor (one upstream and one downstream of the heater) is equal.
Therefore, the temperatures T1 and T2 are equal. When gas flows through
the tube, the upstream sensor is cooled and the downstream sensor is
heated, producing a temperature difference. The temperature difference
T2-T1 is directly proportional to the gas mass flow.

The equation is: ΔT = A * P * Cp * m

Where,

ΔT = temperature difference T2 - T1 (°K)

C

P = heater power (kJ/s)
m = mass flow (kg/s)
A = constant of proportionality (S2-°K2/kJ2)

= specific heat of the gas at constant pressure

p

(kJ/kg-°K)

A bridge circuit interprets the temperature dif ference and a differential
amplifier generates a linear 0-5 Vdc signal directly proportional to the gas
mass flow rate. The flow restrictor shown in Figure 3-1 performs a ranging
function similar to a shunt resistor in an electrical ammeter. The restrictor
provides a pressure drop that is linear with flow rate. The sensor tube has
the same linear pressure drop/flow relationship. The ratio of the restrictor
flow to the sensor tube flow remains constant over the range of the meter .
Different restrictors have different pressure drop s and produce controllers
with different full scale flow rates. The span adjustment in the electronics
affects the fine adjustment of the controller's full scale flow.

In addition to the mass flow sensor , the Model 5850i Mass Flow Controller
has an integral control valve and control circuit, as shown in Figure 3-2.
The control circuit senses any difference between setpoint and the flow
sensor signal and adjusts the current in the modulating solenoid valve to
increase or decrease the flow .

The Model 5850i has the following features incorporated in the integral
control circuit:

Fast Response adjusted by the anticipate potentiometer. This circuit, when

properly adjusted, allows the high frequency information contained in
the sensor signal to be amplified to provide a faster responding flow
signal for remote indication and use by the control valve.

3-1