MKS HPS 945 Series User manual

HPS®Products Series 945
DigitalPirani
Vacuum Sensor System
OPERATION AND
MAINTENANCE MANUAL

Digital Pirani Vacuum Sensor System
HPS®Products Series 945
DigitalPirani
Vacuum Sensor System
July 1999
Part #109450020 Rev. A1

Digital Pirani Vacuum Sensor System
Part#945-X-XXX-XX
–__– ____ __–____
Serial # __ __ __ __ __ __
Please fill in these numbers and have
themreadilyavailablewhencallingfor
serviceoradditionalinformation.
(The part number can be found on your
packing slip, and the serial number is
located on the back panel of the
controller.)
© 1999 by MKS Instruments, Inc. HPS®Products, Inc., All rights reserved.
IsaregisteredtrademarkofMKSInstruments,Inc.,HPSTM Products,Inc.
TeflonisaregisteredtrademarkofDuPontCo.
VCRisaregisteredtrademarkofCajonCo.
Formore information or literature, contact:
MKS Instruments, Inc., HPS®Products, Inc.
5330SterlingDrive
Boulder,CO80301USA
Phone: [phone]
800-345-1967
FAX: [phone]

Digital Pirani Vacuum Sensor System
Table of contents
Table of contents
Package Contents ..................................................................... 1
Symbols Used in this Manual.................................................... 2
Safety Precautions .................................................................... 3
Specifications............................................................................ 5
Controller................................................................................................. 5
SensorTube ...................................................................................... 6
Feature and Control Locations .................................................. 7
Typical Applications for the Series 945 Pirani System .............. 8
About the SensaVac® Series 945 Pirani Vacuum
Sensor System .......................................................................... 9
Installing the Series 945 Pirani System................................... 10
Pirani Sensor Installation .......................................................................10
Location ...........................................................................................10
Orientation .......................................................................................10
Contamination..................................................................................10
Vacuum Connection .........................................................................10
PiraniController Installation....................................................................11
ControllerMounting ..........................................................................11
Connectingthe Sensorto theController...........................................12
AC PowerCord ................................................................................12
FuseReplacement...........................................................................13
AccessoryConnector.......................................................................13
Relay Inductive Loads and Arc Suppression ...................................14
Operating the Series 945 Pirani System.................................. 15
Reading Pressure ...................................................................................15
SensorAdjustment.................................................................................16
Calibratingfor Zero and Atmosphere ......................................................17
Adjusting the Set Point...........................................................................17
Venting to Atmosphere ...........................................................................17
BufferedAnalog Output ..........................................................................18
Usewith Computers ...............................................................................18
LeakDetection .......................................................................................18

Digital Pirani Vacuum Sensor System
Using the Series 945 Pirani System with Other Gases............ 20
Nitrogen Equivalent Pressure .................................................................20
Calibratingfor OtherGases ....................................................................21
Maintaining the Series 945 Pirani System............................... 22
Troubleshootingand Service...................................................................22
Cleaningthe Pirani Controller Front Panel ..............................................22
Cleaning the Pirani Sensor .....................................................................23
Testing the Pirani Sensor .......................................................................23
Accessories............................................................................. 24
ProductWarranty ..................................................................... 25
Notes....................................................................................... 26
Appendix A: How the Series 945 Pirani System Works..........A.1
Theory of aThermal Conductivity Sensor............................................. A.1
Measurement Limits............................................................................. A.1
The Series 945 Pirani System Design Overview .................................. A.2
Amplifier ........................................................................................ A.2
Output............................................................................................ A.2
Set Point Relays ............................................................................A.2
Comparator .................................................................................... A.2
Notes......................................................................................A.3

1
Digital Pirani vacuum Sensor System
Before unpacking your Series 945 Digital Pirani Vacuum Sensor System, check
all surfaces of the packing material for shipping damage.
Please be sure that your Series 945 Pirani System package contains
these items:
1Series 945PiraniController
1 female, 9-pin, subminiature D (D-sub) Accessory connector
1powercord
1 Series 945 Digital Pirani Vacuum Sensor System User's Manual.
The Series 945 System's Pirani Sensor and its connecting cable are sold
separately.Please referto page 24 for necessary ordering information.
If any items are missing from the package, call HPS®Products
CustomerServiceat1-303-449-9861or1-800-345-1967.
Inspect the Series 945 Pirani System for visible evidence of damage. If it has
been damaged in shipping, notify the carrier immediately. Keep all shipping
materials and packaging for claim verification. Do not return the product to
HPS®Products.
Package Contents

2Digital Pirani vacuum Sensor System
The first two symbols below, located on your Series 945 Controller and/or
Sensor, identify critical safety concerns. They are used throughout this
manual to further define the safety concerns associated with the product.
The last two symbols identify other information in this manual that is
essential to highlight or useful in achieving optimal performance from your
Series 945 Pirani System.
CAUTION: Risk of electrical shock.
CAUTION: Refertomanual.
Failure to heed message could result in personal injury
or serious damage to the equipment or both.
Failure to heed message could result in damage to the
equipment.
Informationcallingattentiontoimportantprocedures,
practices, or conditions.
Symbols Used in this Manual

3
Digital Pirani vacuum Sensor System
Safety Precautions
Do not use the Series 945 Pirani System's Sensor with
explosive gas mixtures or gases that are combustible in air.
If the control circuit fails or an exothermic catalytic reaction occurs at the
sensor wire, the wire could ignite the gas mixture.
When using the Series 945 Pirani System with gases other
thanair or nitrogen, avoid overpressure to prevent any
possibility of explosion.
Since the Sensor is calibrated for air/nitrogen, the measured pressure of
another gas will differ from its true pressure. Calibrations diverge widely at
higher pressures. Since the different gases are not linearly related, a gas
correctionfactorcouldleadtohazardousoverpressure.Capacitance
manometersand mechanical dial gauges are best suitedfor higherpressures.
Refer to page 20 for use with other gases.
In a system which is filled from a pressurized source, install a safety relief
valve or burst disc to safely limit pressure.
Turn off power to the Controller before connecting or
disconnecting a cable to the Sensor.
Connecting or disconnecting cables while the Controller is on may damage
the Sensor.
Properlyground the Controller.
The Controller is grounded through the conductor of the power cord. If the
protective ground connection is lost, all accessible conductive parts may
pose a risk of electrical shock. Plug the cord into a properly grounded
outlet only.
When applying a voltage or current to the ports on the rear of the panel, do
not exceed manufacturer's specifications. Electrical shock or Controller
damagemayresult.
Allow only qualified technicians to service the Series 945
Pirani System.
Users should not remove covers, casings, or plug-in components. Injury may
result. Any part replacement or internal adjustments must be performed by a
qualified technician only.

4Digital Pirani vacuum Sensor System
TheSeries 945 Pirani Controller contains lethal voltages
within the casing.
Avoid danger of electrical shock. Unplug the power cord before
opening the casing.
To prevent damage to the Series 945 Pirani Controller,
use the correct line voltage.
Use the Controller with the specified line voltage only. Use a fuse of the
correct type, voltage, and current rating. Only qualified personnel should
change line voltage or fuse ratings if required.
Outside of the U.S., use only a detachable cord set that has conductors with
a cross-sectional area equal to or greater than 0.75 mm2. Power cables
should have agency approval, for example, VDE, Semko, or SEV.
The Series 945 Pirani System and all its accessories must be used as
instructed by MKS Instruments, Inc., HPS®Products Inc., to ensure safe
operation. Use or modification of the equipment in a manner not
consistentwithspecificationsmayrendertheproduct'sinherent
protectionuseless.

5
Digital Pirani vacuum Sensor System
Specifications
MeasuringRange 1.0 x 10-4 to 1.0 x 10+2 Torr
1.0 x 10-1 to 1.0 x 10+5 microns
1.0 x 10-4 to 1.3 x 10+2 mbar
1.0 x 10-2 to 1.3 x 10+4 Pa
UsefulSetPointRange 2.0 x 10-3 to 9.9 x 10+1 Torr
2.0 to 9.9 x 10+4 microns
2.7 x 10-3 to 1.3 x 10+2 mbar
2.7 x 10-1 to 1.3 x 10+4 Pa
Resolution 1% of decade, 10% of decade for
pressuresless than 10-3 Torr
OperatingTemperatureRange 5°to 40°C (41°to 104°F)
StorageTemperatureRange -10°to55°C (14°to 131°F)
OperatingHumidity 80%maximum(noncondensing)
InsulationCoordination Installation(Overvoltage)Category
II,Pollution Degree 2
NumberofChannels 1
FrontPanelControls 2nonvolatile,independentrelayset
points; power on-off switch; zero
adjustment;atmospheric
adjustment
RelayContactRating SPDT, 1 A @ 24 VAC/DC, resistive
RelayResponse 150 msec maximum
PowerRequirement 90 to 130 VAC, 50/60 Hz
or
210 to 250 VAC, 50/60 Hz
PowerConsumption 9 W
Output Voltage 0.20 to 3.25 VDC, buffered
analog, 1 kW maximum output
impedance
Fuse Rating, Size T 0.16 A, Ø5 mm x 20 mm
for 90 to 130 VAC;
T 0.063 A, Ø5 mm x 20 mm
for 210 to 250 VAC
Controller

6Digital Pirani vacuum Sensor System
Display LED with 2 significant digits
(1leading)and1signedexponent;
red,3/5"-high,7-segmentdigits; LED
set point indicators; units shown in
either Torr, mbar, Pascal, or microns
ElectronicCasing Aluminum,anodized
Dimensions 3¾" x 7" x 3¾"
(W x D x H) (96 mm x 178 mm x 96 mm)
Size ¼DIN
Weight 2.2 lb (1.0 kg)
SensorTube
CalibrationGas Air/nitrogen
InstallationOrientation Any
Reproducibility 5% of indicated pressure @ Tconst
MaterialsExposed to Vacuum SS 304, platinum, alumina ceramic,
silver brazing alloy, nickel 200
Internal Volume 0.5 in.3(8.0 cm3) maximum
OperatingTemperatureRange 0°to 50°C (32°to 122°F)
MaximumBakeoutTemperature 50°C(122°F)
Diameter 1.3 in. (34 mm)
Length 4.4 in. (112 mm)
TypicalWeight(withKFFlange) 0.5 lb (0.2 kg)
VacuumConnection KF 16
1/8"NPT-M
with ½" compression seal option
8VCR®-F(½")
11/3"CF(non-rotatable)
2¾"CF(non-rotatable)
Ø15.0 mm x 30.0 mm tubing
Ø18.0 mm x 30.0 mm tubing
Design and/or specifications subject to change without notice.

7
Digital Pirani vacuum Sensor System
12
Rear View
Front View
Side View
Controller
Sensor
Feature and Control Locations
DigitalLED Display
PowerOn-Off Rocker Switch
View Set Point Push-buttons
Set Point Adjustment Potentiometers
LED Set Point Indicators
AtmosphericAdjustmentPotentiometer
ZeroAdjustmentPotentiometer
PowerCordInletw/Fuse Holder
PanelMountingFastenerHoles
Female,9-pin Gauge Port
Male, 9-pin Accessory Port
Slots(for Optional Mounting Brackets)
Male Octal Socket
SensorVacuumPort
!
1
!
2
!
3
!
4
!
5
!
6
!
7
!
8
!
9
!
11
!
12
!
13
!
14
!
10

8Digital Pirani vacuum Sensor System
Typical Applications for the
Series 945 Pirani System
Measuringforeline and roughingpressures generatedby
mechanicalvacuumpumps
Controlling valves and pumps to automate system pump down
using the relay set points
Sensingabnormalpressure andtaking appropriatesecurity
measures using the relay set points
Controlling system pressure usingthe analog output as input to
anautomaticpressurecontroller
Starting or stopping system processes usingtherelay set
points
Measuring pressures of backfilled gases in the range of 10-4 to
10+2Torr
Activating high vacuum sensors at the high end of their
operatingpressurerange

9
Digital Pirani vacuum Sensor System
About the SensaVac®Series 945
Pirani Vacuum Sensor System
The Series 945 Pirani System, together with its Sensor and
connecting cable, provides accurate and reliable data for processes
which need pressure measurement from 10+2 Torr down to 10-4 Torr. It
is low in cost and easy to use.
The Pirani Sensor is available with one of several standard fittings for
vacuum connection. The Sensor connects to the Controller with a
cable that has a female octal socket on one end and a male, 9-pin D-
sub connector on the other. The Controller easily mounts into a ¼DIN
panel cutout or stands alone. All controls, even the power switch, are
conveniently accessed from the front panel, and cable connections are
hidden to the rear of the Controller.
The Series 945 Pirani Controller is
useful either as a small system
controller or as a module in
moresophisticated
pressurecontrol
environments.The
Controllerfeatures
twostandard relay
set points for
process
applications.
Thepressure
readout is a large,
easy-to-readdigital
display. LEDs
indicate the status of
relay set points,
whichare
independently
adjusted using both
a push-button and a
potentiometeronthe
frontpanel.
The analog output and relay contacts are accessible from the
Accessory port on the rear panel.
The Sensor can be located away from the Controller using a cable as
long as 500 feet in length.

10 Digital Pirani vacuum Sensor System
Installing the
Series 945 Pirani System
Pirani Sensor Installation
Location
Locatethe Pirani Sensor where it can measurechamber or manifold pressure.
Install it away from pumps and gas sources and where vibration is minimal to
give the most representative values.
Orientation
Since a Pirani Sensor is designed to minimize convection, operating position
does not affect accuracy. In a standard Pirani system, the atmospheric
pressure reading of a horizontal sensor versus a vertical one differs negligibly
due to residual convection.
The Sensor is factory calibrated vertically with the vacuum port facing down.
Contamination
Locate and orient the Pirani Sensor to avoid contamination which would affect
the tube's element. For example, if the Sensor is installed directly above a
roughingpump, oilvapor could contaminate the tube's filament wire and
cause the calibration to shift.
Install the Sensor with the vacuum port facing down whenever possible to
prevent particulates falling or liquids flowing into it. Using a screen or porous
filter at the port is helpful. Try an HPSTM seal and centering ring assembly
with a screen (see Accessories, p. 24).
VacuumConnection
Standard vacuum interfaces for the Pirani Sensor include:
KF 16 flange 8 VCR®-F (½") fitting
11/3"CF flange Ø15 mm x 30 mm tubing
2 ¾" CF flange Ø18 mm x 30 mm tubing
1/8" NPT-M fitting with a ½" compression seal
To fit the KF 16 port to a KF 10 port, use an HPS®adaptive centering ring
(seeAccessories,p.24).
To fit the Sensor with the 1/8" NPT, do not use the case for tightening. The
Sensor’s vacuum tubing has 9/16" hex flats for tightening. Wrap a layer of
Teflon®tape on the threads of the tubing, in the direction of installation, to
ensurealeak-freeseal.
Instead of the NPT fitting, you may opt to use the ½" O-ring compression
seal against the vacuum tubing above the thread, but the O-ring seal cannot
be used for positive pressure applications .

11
Digital Pirani vacuum Sensor System
Ensure a solid electrical connection between the Sensor
and the grounded vacuum system to shield the tube
elementfromexternalelectromagneticsources.In
applications which the System will be exposed to large
voltage fluctuations, install a centering ring with a screen,
and then ground the screen and tubing.
Pirani Controller Installation
ControllerMounting
TheSeries 945Pirani Controlleris designed for either panel mounting or for
stand-aloneuse.Regardlessofthe method you choose, assureadequate
ventilation to the Controller with at least 1 inch left open above and below the
perforatedpanels.
An optional hardware kit, shown below, is also available for mounting the
Controller into a standard ¼DIN cutout in a panel up to 3/16-inch thick (see
Accessories, p.24). Leave at least 3 inches of clearance behind the
Controllertoaccommodate the connectors andcables.
Mount the Controller into the panel by slipping it through the cutout from the
front. Slide the panel mounting brackets into the slots on either side of the
Controllerfrom the rear, and secure them usingthe thumbscrewsprovided.
Adhesive backed rubber feet for bench top use are provided with the
mounting kit. Remove the adhesive backing from each foot and apply one to
each corner of the aluminum bottom surface.

12 Digital Pirani vacuum Sensor System
ConnectingtheSensor tothe Controller
A sensor cable with a standard octal socket (see Accessories, p. 24) is
required for operation but is purchased separately from the Pirani System.
This socket has an integrated polarizing tab.
The socket has sufficient contact pressure so that strain relief is
unnecessary in most applications, but when exerting excessive stress on the
cable, use separate strain relief to prevent damage to the Sensor or
Controller. Cables are available in standard lengths of 10, 25, 50, and 100 feet
and in custom lengths up to 500 feet.
Connect the cable to the rear of the Controller at the Gauge port. Tighten the
connector jackscrews into the mating screw locks to ensure proper electrical
connection and to prevent stress on the connectors.
Turnoff the Controller before connecting ordisconnectingthe
cable from the Sensor or Controller.
Pin 6 of the octal socket is intentionally shorter as a safety
measure.When the cable is connectedordisconnected from
theSensor,thisfeatureprevents a voltage overload on the
Sensor in case the Controller has not been shut off.
However, it is not possible for this preventative feature to always work, so
avoid any possible damage by always turning off the Controller before any
connectionsaremade.
In applications for which special cables are required, i.e., where the
connectionmust berouted through restrictive barriers or through a conduit,
customize a cable using the figure shown on the following page. Use a D-sub
connector with jackscrews for strain relief in all applications.
ACPower Cord
The Series 945 Pirani System includes a standard, 120 VAC, 50/60 Hz power
cordwith a femaleIEC-320 connector.
If the available power source or connection is different, use only a detachable
cord set with conductors that have a cross-sectional area equal to or greater
than 0.75 mm2. The power cable should be approved by a qualified agency
such as VDE, Semko, or SEV.

13
Digital Pirani vacuum Sensor System
FuseReplacement
The Series 945 Pirani System has a combined fuse holder and power
outlet located on the rear panel of the Controller. Replace the fuse with the
following steps.
1. Unplug the power cord from its outlet.
2. Snap out the fuse holder drawer.
3. Replace the fuse(s) with one of the following time-lag fuses:
T 0.16 A (Ø5 mm x 20 mm) –90 to 130 VAC
T 0.063 A (Ø5 mm x 20 mm) –210 to 250 VAC.
4. Close and secure the fuse holder drawer.
AccessoryConnector
Relay set point contacts and the analog output voltage can be accessed from
the Accessory port on the rear panel of the Controller. A connector kit to mate
to the port is provided. The figure and chart on the next page identify the pin
functions of the Accessory port.
Do not inadvertently short circuit the set point relay terminals to
theanalogoutput voltage.

14 Digital Pirani vacuum Sensor System
RelayInductive Loads and Arc Suppression
If the set point relay is used to switch inductive loads, e.g., solenoids, relays,
transformers, etc., the arcing of the relay contacts may interfere with
Controlleroperationor reduce relay contact life.Thereforeanarcsuppression
network, shown schematically below, is recommended. The values of the
capacitance C and the resistance R are calculated by the equations,
C = I
2/(1 x 107) and
R = E/10I
a
where,
C is in farads
R is in ohms
I is DC or ACpeak load current in amperes
E is DC or ACpeak source voltage in volts
a = 1 + (50/ E ).
Note that,
R
min
= 0.5 Ωand C
min
= 1.0 x 10-9 F.
Pin Description
1 Set point relay 1 - normally closed contact
2 Set point relay 1 - normally open contact
3 Set point relay 2 - common
4 Notused
5 Analogoutput voltage(+)
6 Set point relay 1 - common
7 Set point relay 2 - normally closed contact
8 Set point relay 2 - normally open contact
9 Analogoutputvoltage (-)
9-pin Accessory port
15
9
6
E
RC