Download 344 Vacuum Gauge Controller Manual

Series 344
Granville-Phillips® Series 344
Vacuum Gauge Controller
Instruction Manual
Instruction manual part number 344005
Revision C - November 2016
16
Series 344
Granville-Phillips® Series 344
Vacuum Gauge Controller
This Instruction Manual is for use with the following GranvillePhillips catalog numbers:
344001, 344002, 344003, 344011, 344012, 344013, 344014,
344015, 344016, 344017, 344018
Customer Service / Technical Support:
MKS Pressure and Vacuum Measurement Solutions
®
MKS Instruments, Inc., Granville-Phillips Division
6450 Dry Creek Parkway
Longmont, Colorado 80503 USA
Tel: 303-652-4400
Fax: 303-652-2844
Email: [email protected]
MKS Corporate Headquarters
MKS Instruments, Inc.
2 Tech Drive, Suite 201
Andover, MA 01810 USA
Tel: 978-645-5500
Fax: 978-557-5100
Email: [email protected]
Instruction Manual
© 2016 MKS Instruments, Inc. All rights reserved.
®
®
Granville-Phillips and Stabil-Ion are registered trademarks, and mksinstTM is a
trademark of MKS Instruments, Inc. All other trademarks and registered
trademarks are the properties of their respective owners.
RECEIVING INSPECTION
On receipt of your equipment, inspect all material for damage. Confirm that the shipment includes
all items ordered. If items are missing or damaged, submit a claim as stated below for a domestic
or international shipment, whichever is applicable.
If materials are missing or damaged, the carrier that made the delivery must be notified within 15
days of delivery, or in accordance with Interstate Commerce regulations for the filing of a claim.
Any damaged material including all containers and packaging should be held for carrier
inspection. Contact our Customer Service Department, 6450 Dry Creek Parkway, Longmont,
Colorado 80503, telephone (303) 652-4400, if your shipment is not correct for reasons other than
shipping damage.
INTERNATIONAL SHIPMENT
Inspect all materials received for shipping damage and confirm that the shipment includes all
items ordered. If items are missing or damaged, the airfreight forwarder or airline making delivery
to the customs broker must be notified within 15 days of delivery. The following illustrates to
whom the claim is to be directed.
• If an airfreight forwarder handles the shipment and their agent delivers the shipment to
customs, the claim must be filed with the airfreight forwarder.
• If an airfreight forwarder delivers the shipment to a specific airline and the airline delivers the
shipment to customs, the claim must be filed with the airline.
Any damaged material including all containers and packaging should be held for carrier
inspection. If your shipment is not correct for reasons other than shipping damage, contact our
Customer Service Department, 6450 Dry Creek Parkway, Longmont, Colorado 80503, U.S.A., or
telephone (303) 652-4400.
LIMITED WARRANTY
These Granville-Phillips products are warranted against defects in materials and workmanship for
one year from the date of shipment provided the installation, operating and preventive
maintenance procedures specified in this instruction manual have been followed. Granville-Phillips
will, at its option, repair, replace or refund the selling price of the product if Granville-Phillips
determines, in good faith, that it is defective in materials or workmanship during the warranty
period, provided the item is returned to Granville-Phillips together with a written statement of the
problem.
Defects resulting from or repairs necessitated by misuse or alteration of the product or any cause
other than defective materials or workmanship are not covered by this warranty. GRANVILLEPHILLIPS EXPRESSLY DISCLAIMS ANY OTHER WARRANTY, WHETHER EXPRESSED OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. UNDER NO
CIRCUMSTANCES SHALL GRANVILLE-PHILLIPS BE LIABLE FOR CONSEQUENTIAL OR
OTHER DAMAGES RESULTING FROM A BREACH OF THIS LIMITED WARRANTY OR
OTHERWISE.
WARNING
READ THIS INSTRUCTION MANUAL BEFORE INSTALLING, USING, OR SERVICING THIS
EQUIPMENT. IF YOU HAVE ANY DOUBTS ABOUT HOW TO USE THIS EQUIPMENT
SAFELY, CONTACT THE GRANVILLE-PHILLIPS CUSTOMER SERVICE DEPARTMENT AT
THE ADDRESS LISTED ON THIS MANUAL.
DANGER, HIGH VOLTAGE
180V is present in the power supply, on the cable, and at the ion gauge tube when the tube is
turned on.
EXPLOSIVE GASES
Do not use the 344 Vacuum Gauge Controller to measure the pressure of explosive or
combustible gases or gas mixtures. Ionization gauge filaments operate at high temperatures.
IMPLOSION AND EXPLOSION
Glass ionization gauges if roughly handled may implode under vacuum causing flying glass which
may injure personnel. If pressurized above atmospheric pressure, glass tubes may explode. A
substantial shield should be placed around vacuum glassware to prevent injury to personnel.
Danger of injury to personnel and damage to equipment exists on all vacuum systems that
incorporate gas sources or involve processes capable of pressurizing the system above the limits
it can safely withstand.
For example, danger of explosion in a vacuum system exists during backfilling from pressurized
gas cylinders because many vacuum devices such as ionization gauge tubes, glass windows,
glass bell jars, etc, are not designed to be pressurized.
Install suitable devices that will limit the pressure from external gas sources to the level that the
vacuum system can safely withstand. In addition, install suitable pressure relief valves or rupture
discs that will release pressure at a level considerably below that pressure which the system can
safely withstand.
Confirm that these safety devices are properly installed before installing the 344 Vacuum Gauge
Controller. In addition, check that (1) the proper gas cylinders are installed, (2) gas cylinder valve
positions are correct on manual systems, and (3) the automation is correct on automated
systems.
WARNING
Operation of the 344 Vacuum Gauge Controller with line voltage other than that selected by the
power supply voltage selector switch can cause damage to the instrument and injury to personnel.
WARNING
Do not attach cables to glass gauge pins while the gauge is under vacuum. Accidental bending of
the pins may cause the glass to break and implode. Cables once installed should be secured to
the system to provide strain relief for the gauge tube pins.
WARNING
Safe operation of vacuum equipment, including the 344 VGC, requires grounding of all exposed
conductors of the gauges and the controller and the vacuum system. LETHAL VOLTAGES may
be established under some operating conditions unless correct grounding is provided.
Research at Granville-Phillips has established that ion producing equipment, such as ionization
gauges, mass spectrometers, sputtering systems, etc., from many manufacturers may, under
some conditions, provide sufficient conduction via a plasma to couple a high voltage electrode to
the vacuum chamber. If conductive parts of the chamber are not grounded, they may attain a
potential near that of the high voltage electrode during this coupling. Potentially
fatal electrical shock could then occur because of the high voltage between these chamber parts
and ground.
During routine pressure measurement using ionization gauge controllers from any manufacturer,
about 160V may become present on ungrounded chambers at pressures near 10-3 Torr. All
isolated or insulated conductive parts of the chamber must be grounded to prevent these voltages
from occurring.
Grounding, though simple, is very important! Please be certain that the ground circuits are
correctly utilized, both on your ion gauge power supplies and on your vacuum chambers,
regardless of their manufacturer, for this phenomenon is not peculiar to Granville-Phillips
equipment. Refer to Safety Instructions and Section 2.4, Installation, for additional information. If
you have questions, or wish additional labels or literature, please contact one of our technical
personnel.
TABLE OF CONTENTS
Page
CHAPTER 1 INTRODUCTION
CHAPTER 2 VGC INSTALLATION AND OPERATION
2.1 AC Line Voltage
2.2 Mounting
2.3 Ionization Gauge Types and Installation
2.4 System Ground Test Procedure
2.5 Control and Status Connector
2.6 Degas
2.7 Emission Current Adjustment
2.8 Ion Gauge Cables
2.9 Electrometer Operation
2.10 Protective Shutdowns
1-1
2-1
2-2
2-2
2-3
2-4
2-4
2-7
2-8
2-9
2-12
CHAPTER 3 VGC CALIBRATION
3.1 Introduction
3.2 Relative Gas Sensitivities
3.3 Adjusting Emission Current
3.4 Electrometer Calibration
3-1
3-3
3-3
3-4
CHAPTER 4 THEORY OF OPERATION
4.1 Ion Gauge Theory
4.2 Vacuum Gauge Controller
4-1
4-2
CHAPTER 5 SPECIFICATIONS
5-1
CHAPTER 1
INTRODUCTION
General Description
The 344 Vacuum Gauge Controller (VGC) provides power, control, biasing and ion
current measurement for up to eight hot filament ionization gauges. All gauges can be
operated simultaneously while one gauge at a time can be degassed using resistance
2
grid heating (I R). Control and status of the gauges are electrically isolated logic
inputs/outputs and pressure is monitored via analog outputs. All signals are through a 40
pin header connector on the rear panel.
The 344 VGC is packaged in a 19 inch x 5.25 inch high rack mount chassis. The chassis
is a card cage accommodating one I/O (input/output) module and a maximum of eight IG
modules. The IG modules may be removed through the front panel without removal of
the chassis from the instrument rack. Blank modules are available for unused spaces.
Components
344001 - Vacuum Gauge Controller Basic. This is comprised of the chassis, power
transformer, bus circuit board and I/O module. It requires one IG module for each ion
gauge to be operated.
344002 - Ion Gauge Module. The IG Module houses circuitry to control the emission
current and grid voltage of the gauge as well as the electrometer circuit for measuring ion
current. Protective shutdowns for filament over-power, grid over-current and overpressure also are on the IG module. The filament protection fuse is on the front panel
while the Ion Gauge connector is on the rear.
344003 - I/O Module. The Input/Output Module circuits electrically isolate external logic
signals from internal logic levels and ground. Logic decoding and line voltage selection
are also provided here. The front panel holds the grid and degas fuses. The I/O
connector to the system control is on the rear panel.
344004 - Blank Module. This module fills a space not occupied by an IG Module. It
provides a cosmetic function as well as a safety barrier when fewer than eight IG Modules
are used.
CHAPTER 2
VGC INSTALLATION AND OPERATION
2.1 Line Voltage Selection
The 344 VGC is designed to operate from 115 Vac nominal line voltage, 50 to 60 Hertz.
Verify power source before connecting the controller.
WARNING
Operation of the VGC with incorrect line voltage applied can cause damage to the
equipment and injury to personnel.
2.2 Mounting
The 344 VGC can be easily rack mounted in a standard 5.25 inch space using supplied
hardware. The chassis is ventilated by vents on each side. These areas must be free of
obstructions and access should be provided to the connectors and fuse holder on the rear
panel and to the fuse holders on the front. Ambient air temperature should not exceed
o
o
50 C (122 F).
2.3 Ionization Gauge Types And Installation
WARNING
Do not attach cables to glass gauge pins while the gauge is under vacuum.
Accidental bending of the pins may cause the glass to break and implode. Cables,
once installed, should be secured to the system to provide strain relief for the
gauge tube pin.
The 344 VGC is designed to operate 8 Bayard-Alpert type or equivalent ionization gauges.
Coated iridium filament type gauges are recommended since at higher pressures iridium
filaments provide longer operating life and greater burnout resistance. When installing
your ion gauge, note that if placed near the pump, the pressure in the gauge may be
considerably lower than in the rest of the system. If placed near a gas inlet or source of
contamination, the pressure in the gauge may be higher.
If an unshielded gauge is placed near an electron beam evaporation source or used in a
sputtering system, spurious electrons or ions may disturb the measurement. Screens or
other shielding should be placed between the gauge and the system if spurious charged
particles or severe electromagnetic interference is present. Consideration should also be
given to electrostatic shielding of glass tubulated gauges when measuring pressures near
their x-ray limits.
2.4
System Ground Test Procedure (Refer to the Safety Instructions on p. 0-4 for further
information)
Procedure: Physically examine the grounding of both the 344 VGC and the vacuum
chamber. Is there an intentional heavy duty ground connection to all exposed conductors
on the vacuum chamber? There should be. Note that an "O" ring or "L" ring gasket,
without metal clamps, can leave the chamber on one side electrically isolated. Power can
be delivered to mechanical and diffusion pumps without any ground connections to the
system frame or chamber. Water line grounds can be lost by a plastic or rubber tube
interconnection. What was once a carefully grounded vacuum system can, by innocent
failure to reconnect all ground connections, become a very dangerous device. Use the
following procedure to test each of your vacuum systems which incorporates an ionization
gauge.
This procedure uses a conventional Volt-Ohm Meter (VOM) and Resistor (10 ohm,
10 watt).
1.
With the gauge controller turned off, test for both dc and ac voltages between the metal
parts of the vacuum chamber and the power supply chassis.
2.
If no voltages exist, measure resistance. The resistance should not exceed 2 ohms. Two
ohms, or less, implies commonality of these grounds that should prevent the plasma from
creating a dangerous voltage between them. This test does not prove that either
connection is earth ground, only that they are the same. If more than 2 ohms is indicated,
check with your electrician.
3.
If ac or dc voltages exist and are less than 10 volts, shunt the meter with a 10 ohm, 10
watt resistor. Repeat the voltage measurement. With the shunt in place across the meter,
if the voltage remains at 83% or more of the unshunted value, commonality of the grounds
is implied. Repeat the measurements several times to be sure that the voltage ratio is not
changing with time. If
Voltage(shunted)
= .83moremore,
Voltage(unshunted)
this should prevent the plasma from creating a dangerous voltage between these grounds.
If more than 10 volts exists between grounds, check with your electrician.
4.
If the voltage change in step 3 is greater than 17% due to the placement of the shunt, it
complicates the measurement. The commonality of the grounds may be satisfactory and
the coupling poor, or the commonality could be poor! Your electrician should be asked to
check the electrical continuity between these two ground systems. The placement of a
second ground wire (dashed line in Fig. 2.2) between the vacuum chamber and the ion
gauge controller chassis is not a safe answer, for large currents could flow through it.
Professional help is recommended.
2.5
Control and Status Connector
The 344 VGC is intended as a slave device to a programmable controller, system
computer or manual switch panel. All inputs and outputs are electrically isolated from
internal circuitry, thus an external power supply must provide 24 Vdc to implement the
control inputs and status outputs. Connections to the I/O of the 344 VGC are via a 40 pin
header connector on the rear panel of the I/O Module.
The logic states shown are positive true logic and the voltages are with reference to the 24
volt Logic Power Supply negative terminal.
2.6 Degas
One gauge tube may be degassed at a time. The gauge is selected with the three Degas
Select inputs and the Degas Enable input according to the truth table of Fig. 2.5. Again,
the logic is positive true and voltages reference to the Logic Power Supply negative. Note
that Degas Enable must go to logic 1 state (no gauge selected) when switching degas
among gauges to avoid ambiguous logic combinations. Also, the 344 VGC requires that
the IG filament be on in order to degas the gauge.
Pressure within the gauge is measured by the electrometer during degas. It is strongly
-5
recommended that the pressure be below 5 x 10 Torr when degas is switched on. This
pressure is sufficiently low to pump degassed contaminants from the gauge elements as
they are heated.
Function
Filament On/Off (Input)
Emission Current Select (Input)
Degas Select (Input)
(See Fig. 2.5)
Pin
IG1
IG2
IG3
IG4
IG5
IG6
IG7
IG8
1
3
5
7
9
11
13
15
IG1
IG2
IG3
IG4
IG5
IG6
IG7
IG8
4
8
12
16
19
23
20
24
Bit 3
Bit 2
Bit 1
26
27
25
Most Significant Bit (4)
(2)
Least Significant Bit (1)
28
Low = Enable
Must go to Hi while Degas Select data
is changing.
+
-
40
39
24 Vdc ± 10%
Isolated from internal
supplies and analog ground
IG1
IG2
IG3
IG4
IG5
IG6
IG7
IG8
2
6
10
14
17
21
18
22
Degas Enable (Input)
(see Fig. 2.5)
Logic Power Supply (Input)
Gauge Status (Output)
Analog Ground
Electrometer
Analog Outputs
Comments
29,30
IG1
IG2
IG3
IG4
IG5
IG6
IG7
IG8
31
32
33
34
35
36
37
38
Low = 0 V or short to Logic Supply negative terminal (pin 39)
Hi = 24 V or open circuit (internal passive pull-ups provided)
Low = On
Low = 1 mA Emission
Hi = 0.1 mA Emission
Low = On
*Important* This Must Be Isolated
From Logic Supply For Input/Output
Isolation
-v
Pressure = 10
Refer to Fig. 2.9, 2.10, 2.11
Function
Degas
Sel 3
Degas
Sel 2
Degas
Sel 1
Degas
Enable
Pin #
26
27
25
28
Degas
Selected
IG1
IG2
IG3
IG4
IG5
IG6
IG7
IG8
None
1
1
1
0
0
0
0
1
X
1
0
0
1
1
0
0
1
X
0
1
0
1
0
1
0
1
X
0
0
0
0
0
0
0
0
1
0 = Low Input = 0 Vdc or short to logic supply negative terminal
1 = Hi Input = 24 Vdc or open circuit (internal passive pull-ups are provided.
X = Don't care = 0 or 1
NOTE: IG filament must be on to enable degas for that gauge.
NOTE: Degas enable must go to logic 1 (no gauge selected) when changing Degas Select inputs to avoid
ambiguous logic combinations.
2.7
Emission Current Adjustment
The 344 VGC is factory calibrated to operate gauges with a sensitivity of 10/Torr for
nitrogen gas. This calibration is valid for both glass tubulated (encapsulated) and nude
2
Bayard-Alpert ionization gauges with I R degassable grids. (The grids of these gauges
are typically configured as a bifilar helix). When using a gauge with a sensitivity
different than 10/Torr or when measuring a gas other than N2 consult paragraphs 3.1
through 3.3 of this manual to compensate for this difference. The emission adjust
potentiometer is located at the top edge of the IG Module as shown in Fig. 3.1. It is
accessed by either connecting the Module to the chassis with an extender board or by
removing the top cover of the chassis.
2.8
Ion Gauge Cables
Ionization gauge connections are accessed at the rear panel on four pin, twist lock
connectors, AMP #206430-1. Granville-Phillips can supply cables for glass tubulated or
nude ion gauges in lengths of 10 to 60 feet. In special installations as where the cable
must route through bulkheads or conduit, it may be necessary to build a custom cable to
suit your needs. Figures 2.6, 2.7 and 2.8 show gauge tube connections and cable
wiring for standard Bayard-Alpert type gauges. The coaxial cable from the gauge tube
collector to the VGC electrometer is bundled within the gauge cable (in Granville-Phillips
cables). If necessary the coax could be routed separately; however, it is advisable to
route the collector cable parallel with the gauge cable to minimize inductively coupled
ground currents which may cause pressure reading errors.
Cable for Glass Tubulated Ion Gauge (Bayard-Alpert)
Cable for Nude Ion Gauge
2.9
Electrometer Operation
The electrometer circuitry of the IG Module is a logarithmic amplifier which produces an
output voltage proportional to the logarithm (base ten) of the gauge pressure.
For a 10/Torr gauge with emission current of 1.0 mA
V out = - log10 P oreP = 10V out
For a 10/Torr gauge with emission current of 0.1 mA
(1-V out )
V out = 1 - log10 P oreP = 10
The electrometer analog output is accessed on the rear panel connector of the I/O
Module. Refer to figures 2.3 and 2.4.
Figures 2.9, 2.10 and 2.11 show Vout versus pressure for 1 mA and 0.1 mA emission
currents in tabular and graphical formats. If emission current is other than 1 or 0.1 mA
or if gauge sensitivity is not 10/Torr, refer to section 3.1 to calculate resultant ion
current. Analog output voltage is related to ion current by:
V out = -(2 + LogI + )
EMISSION CURRENT (I-) = 1 mA
PRESSURE (TORR)
Gauge Off
-9
1 x 10
-8
1 x 10
-7
1 x 10
-6
1 x 10
-5
1 x 10
-4
1 x 10
-3
1 x 10
-3
2 x 10
ION CURRENT (I+)
(AMPERES)
0
-11
1 x 10
-10
1 x 10
-9
1 x 10
-8
1 x 10
-7
1 x 10
-6
1 x 10
-5
1 x 10
-5
2 x 10
VOUT (VOLTS)
_10.000
9.000
8.000
7.000
6.000
5.000
4.000
3.000
2.699
Electrometer Response, I- = 1 mA, S = 10/Torr
EMISSION CURRENT (I-) = 0.1 mA
PRESSURE (TORR)
Gauge Off
-8
1 x 10
-7
1 x 10
-6
1 x 10
-5
1 x 10
-4
1 x 10
-3
1 x 10
-2
1 x 10
-2
1 x 10
ION CURRENT (I+)
(AMPERES)
0
-11
1 x 10
-10
1 x 10
-9
1 x 10
-8
1 x 10
-7
1 x 10
-6
1 x 10
-5
1 x 10
-5
1 x 10
VOUT (VOLTS)
_10.000
9.000
8.000
7.000
6.000
5.000
4.000
3.000
2.699
Electrometer Response, I- = 0.1 mA, S = 10/Torr
2.10
Protective Shutdowns
The 344 VGC provides three detection circuits which limit damaging conditions in the ion
gauge tube. Any of these protective circuits will shut off the affected gauge but will not
affect operation of the remaining seven gauges. The protective circuitry is located on
the IG Module.
Overpressure Shutdown
This circuit compares the electrometer output with a fixed reference voltage. Thus the
overpressure shutdown is at a fixed ion (collector) current (100 µA). The gauge
pressure for this ion current is dependent on the selected emission current since
P=
1 I+
S I-
where P = Pressure (Torr)
S = Gauge sensitivity (1/Torr)
I+ = Ion current (Amperes)
I- = Emission current (Amperes)
-2
For an emission current of 1 mA (10/Torr gauge), the gauge will shut off at 1 x 10 Torr.
-1
For an emission current of 0.1 mA, the gauge will shut off at 1 x 10 Torr.
Filament Overvoltage Shutdown
This circuit indirectly measures the RMS voltage applied to the gauge filament and shuts
off the gauge if this exceeds a limit. This situation can occur if the gauge is not
connected to the VGC or if the pressure in the gauge is so high that no emission current
can flow (e.g., atmospheric pressure) or if the emissive coating on the filament has
eroded. Since the filament power control circuit responds relatively slowly (to prevent
thermal oscillation) the overvoltage shutdown may take several seconds to respond to
an error condition.
Grid Overcurrent Shutdown
Each IG Module employs a circuit to turn off power to the gauge if the grid current
exceeds a fixed limit of 15 milliamperes. Such a condition implies that a short circuit or
shunt has occurred in the gauge or the cable. The circuit responds very quickly to an
overcurrent condition removing grid and filament voltage.
CHAPTER 3
VGC CALIBRATION
3.1
Introduction
The 344 VGC is factory calibrated to measure pressure of nitrogen gas using gauge tubes
with sensitivity of 10/Torr. To conveniently read the pressure in gauges of a different
sensitivity or of other gases, it is necessary to adjust the emission current in the gauge.
The adjustment is described in paragraph 3.3.
Calibration of the electrometer circuitry is a delicate procedure requiring precision
laboratory instruments. It is unlikely that this calibration will change over time; however,
the procedure is detailed in paragraph 3.4.
Gauge Sensitivity
An ionization gauge determines pressure by measuring the ratio of two currents in the
gauge where:
Pressure =
1 I+
1 collector current
=
S emission current
S I-
S = gauge sensitivity constant
Sensitivity, S, is a value determined by design and measured empirically under controlled
conditions. A typical Bayard-Alpert ionization gauge, such as the Granville-Phillips 274,
measuring nitrogen gas has a sensitivity of 10/Torr. Several companies, in addition to the
National Institute of Science and Technology, offer the service of measuring the sensitivity
of a gauge. This may be necessary for precise low pressure measurement although
manufacturer's specified sensitivity is sufficient for the vast majority of applications.
Since the electrometer measures the collector current, I+, of the above equation with a
fixed gain, variation of gauge sensitivity may be compensated by changing the emission
current, I-, or by mathematically manipulating the electrometer output voltage to know the
pressure. The examples below illustrate these two methods.
Example: In using the 344 VGC, I would like to measure pressure with a gauge which has
a sensitivity of 8/Torr instead of the calibrated 10/Torr. I have two ways to accomplish this:
1)
For the electrometer to have the same output voltage as for a 10/Torr gauge (i.e.,
indicate the same pressure): Collector current (10/Torr) = Collector current
(8/Torr) or:
I + (10) = I + (8)at Pressure = P
where I+ (10) = collector current for a 10/Torr gauge. From the ion gauge
equation:
P=
1 I + (8) 1 I + (10)
=
8 I - (8) 10 I - (10)
re-arranging:
I - (8) = 1.25 I -(10)
Therefore, to make the 8/Torr gauge read the same electrometer output voltage as
a 10/Torr gauge at any pressure, I can adjust the emission current to 1.25 · 1.0 mA
= 1.25 mA. Pretty easy, huh?
2)
If I wish to read pressure for the 8/Torr gauge from my system control computer I
can do so without adjusting emission current by applying some simple software
math. In this case at pressure, P:
P=
1 I + (8)
1 I + (10)
=
as above
8 I - (8)
10 I - (10)
where,
I + (10) = collector current for a 10/Torr gauge
In this case, though, I will leave the emission current the same, i.e., I- (8) = I- (10),
so,
1 I + (8)
1 I + (10)
=
8 I - (10)
10 I - (10)
re-arranging:
I + (10) = 10 = 1.25
8
I + (8)
So the collector current from the 10/Torr gauge is 1.25 times the collector current
from a 8/Torr gauge at any pressure. Since the voltage output of the electrometer
-V
is a logarithmic relationship: (for I+ = 1.0 mA) P = 10 , the pressure in an 8/Torr
-V
gauge as output from a 10/Torr calibrated electrometer is simply: P = 1.25 x 10 .
Hence, I will put a gauge calibration factor of 1.25 in my pressure calculation
software.
3.2
Relative Gas Sensitivities
Sensitivity depends on the gas being measured as well as the type of IG tube. Fig. 3.1
lists the relative gauge sensitivities for common gases. These values are from NASA
Technical Note TND 5285, "Ionization Gauge Sensitivities as Reported in the Literature",
by Robert L. Summers, Lewis Research Center, National Aeronautics and Space
Administration. Refer to this technical note for further definition of these average values
and for the gauge sensitivities of other gases.
To calculate the sensitivity Sx for gas type x:
S x = R x . SN 2
Where SN2 is the gauge sensitivity for N2 and Rx is found from Fig. 3.1.
GAS
Rx
GAS
Rx
He
Ne
D2
H2
N2
Air
02
0.18
0.30
0.35
0.46
1.00
1.00
1.01
H20
N0
Ar
C02
Kr
SF6
Xe
1.12
1.16
1.29
1.42
1.94
2.50
2.87
Fig. 3.1 Relative Gas Sensitivities
To correct for change in sensitivity due to gas composition, apply the corrections as shown
in the preceding example.
3.3
Adjusting Emission Current
To set emission current in the 344 VGC, extend the appropriate IG Module on an extender
board or remove the chassis top cover by loosening the two screws on the back panel at
the top. Locate the emission adjust potentiometer using Fig. 3.2. Connect a voltmeter (2
volts full scale) across CR6 located to the left of the pot. 1.0 volt across the diode is
equivalent to 0.1 mA emission with the Emission Current Select input (of I/O connector) in
the logic high or open circuit state. 1.0 volt across the diode is equivalent to 1.0 mA
emission with the Emission Current Select input in the low state. Adjust the potentiometer
to give the emission current required. The range of adjustment is 0.85 to 1.35 volts.
Fig. 3.2 IG Module
3.4
Electrometer Calibration
-
The electrometer of the IG Module is calibrated at the factory for accuracy between 1 x 10
-3
Torr and 1 x 10 Torr. Normally, no further adjustment is required; however, the
following procedure may be used to re-calibrate.
9
The electrometer has three potentiometers to adjust: OFFSET, SCALE, and ZERO.
These pots are labeled on the circuit board silkscreen as R32, R33 and R34 and are
shown in Fig. 3.2.
Equipment required:
DC picoampere current source - 10 pA to 10 µA (e.g.,
Cable for current source to electrometer input
Digital voltmeter, 4-1/2 digit
Extender card for IG Module
Adjusting screwdriver
Keithley 220)
Procedure:
1)
Connect cable from current source to the IG coax input.
2)
Connect DVM to IG analog output and ground (refer to Fig. 3.3) of the I/O module
connector.
3)
Connect an ion gauge simulator or an ion gauge to the IG gauge connector and
turn on the gauge.
4)
-8
Set current source to 1 x 10 Amp (10 nA).
5)
Adjust IG OFFSET pot (R32) to give a DVM reading of 6.000 V ± 0.002 V.
6)
-6
Set current source to 1 x 10 Amp (1 µA).
7)
Adjust IG SCALE pot (R33) to give a DVM reading of 4.000 V ± 0.002 V.
8)
-11
Set current source to 1 x 10 Amp (10 pA). Note: Reduce the current slowly in
the picoampere range to avoid saturating the amplifier.
9)
Adjust IG ZERO pot (R34)
to give a dvm READING OF 9.00 v ± 0.010 v. The
response of the logarithmic amplifier is slow in the picoamp range.
10)
-10
-9
Set the current source to even decade values (1 x 10 , 1 x 10 , etc.) and verify
that the analog output responds -1 volt per decade (8.000, 7.000, etc.). Refer to
Fig. 2.11 for input currents versus output voltages.
Input
IG1
IG2
IG3
IG4
IG5
IG6
IG7
IG8
Analog Output*
Pin 31
Pin 32
Pin 33
Pin 34
Pin 35
Pin 36
Pin 37
Pin 38
*Output voltages relative to analog ground (pins 29 and 30)
Fig. 3.3 Calibration Measurement Points
CHAPTER 4
THEORY OF OPERATION
4.1
Ion Gauge Theory The functional parts of a typical ionization gauge are the filament (cathode), grid (anode)
and ion collector, shown schematically in Fig. 4.1. These electrodes are maintained by the
gauge controller at +30, +180, and 0 volts, relative to ground, respectively.
The filament is heated to a high temperature so that
electrons are emitted and accelerated toward the
grid by the potential difference between the grid and
filament. All the electrons eventually collide with the
grid, but many first traverse the region inside the grid
one or more times.
Fig. 4.1 Ion Gauge Schematic
When an energetic electron collides with a gas molecule, an electron may be dislodged
from the molecule, leaving it with a positive charge. Most ions are then attracted to the
collector. The rate at which electron collisions with molecules occur is proportional to the
density of gas molecules, and hence the ion current is proportional to the gas density (or
pressure, at constant temperature).
The amount of ion current for a given emission current and pressure depends on the ion
gauge design. This gives rise to the definition of ion gauge "sensitivity", denoted in this
manual by "S".
S = ion current / (emission current x pressure)
Bayard-Alpert type gauges typically have sensitivities of 10/Torr when used with nitrogen
or air. Sensitivities for other gases are given in Fig. 3.1.
The ion gauge controller varies the heating current to the filament to maintain a constant
electron emission, and measures the ion current to the collector. The pressure is then
calculated from these data.
2
2
Ion gauge degas is accomplished by resistance heating (I R). During I R degas, a large
current is passed through the grid structure, raising its temperature and driving off
2
contaminants. Note that some ion gauge designs do not allow I R degas.
4.2
Vacuum Gauge Controller The 344 VGC contains the following circuit blocks to correctly bias and control a hot
filament ionization gauge and measure ion current.
Low voltage supply - provides ± 12 volts for logic and op amp power and biasing within the
power supply. The common of this supply is "Analog Ground" which is isolated from the
+24 volt logic input. This supply consists of two full wave, center-tapped rectifiers, filter
capacitors and fixed linear regulators.
Grid bias supply - provides +180 Vdc for biasing the grids of the ionization gauges. It
consists of a full wave rectifier, filter capacitor and series pass regulator. Additionally,
each gauge has an overcurrent sense circuit which couples to the filament logic circuit to
switch off the gauge in a fault condition and a relay to isolate the grid from its supply when
the filament is off.
Degas supply/control - selects the gauge to be degassed based on the "degas Select" and
"Degas Enable" logic inputs from the user. The circuit isolates these logic inputs and
decodes the bit pattern to select none or one of the IG's. A relay of the selected gauge
then applies 9 volts AC to the grid of the tube causing the temperature of the gauge to
increase thus desorbing impurities from gauge components. Please note that degas
control relies on the user's control equipment to determine that the pressure within the
gauge is sufficiently low to preclude damage. The gauge filament must be on to enable
degas.
Filament logic - switches the gauge on or off according to various inputs. The "Filament
on/off" signal from the I/O connector is optically isolated and drives the set input of an R-S
flip-flop. The reset input comes from three sources: The grid overcurrent sensor, the
electrometer overpressure detector, and the filament overvoltage comparator. The latter
determines if the filament drive circuit has exceeded specified bounds. When a shut-down
signal is received by the filament logic, the filament control circuit is forced to the off state,
the grid relay is switched off and the filament status output goes into open collector state.
Emission control - circuit senses the emission current flowing from grid to filament in the
gauge. This signal is the feedback for the amplifier which controls filament heating power
thus precise control of emission current is obtained. The output of the emission control
amplifier is compared with the AC line frequency. The resultant output switches a triac to
pulse width modulate the AC heating power to the filament. Excessive power to the tube
is obviated by the overvoltage comparator sensing the output of the control amplifier and
shutting off the triac drive signal.
Electrometer - is a logarithmic current input - voltage output amplifier. As with most log
amplifiers, the electrometer uses a p-n junction as a feedback impedance with a matching
junction for temperature compensation. A subsequent amplifier adds an offset to produce
the -1 volt per decade of input current.
CHAPTER 5
SPECIFICATIONS
344001 Vacuum Gauge Controller
Physical
Width
Height
Depth
Weight
18.95 in.
5.2 in.
9.0 in.
34 lbs.
Electrical
Voltage
Frequency
Power
Primary Fuse
Environmental
105-125 Vac
50 to 60 Hz
400 watts maximum
4.0 A S.B.
o
0 to 50 C operating temperature
0 to 80% RH non-condensing
Ion Gauge
Emission Current
0.085 to 0.130 mA, or 0.85 to 1.30 mA, adjustable
Collector Potential
Grid Potential
Filament Potential
Degas
0 Vdc*
+180 Vdc*
+30 Vdc*
2
I R (resistance heating) 10 V, 6 A
Logic Input/Output
Logic Supply (input
24 Vdc ± 10% isolated from internal supplies and analog
ground.
Filament Control (input)
8 inputs, active low (0 V), optically isolated. Low = filament
on.
Current: Low 1.7 mA (maximum); High 0 mA.
Degas Control (inputs)
4 inputs, active low, optically isolated. Refer to Fig. 2.6 for
logic.
Current: Low 1.7 mA (maximum); High 0 mA.
Emission Select (input)
8 inputs, active low, magnetically isolated. Low = 1 mA
emission range.
Current: Low 12 mA (maximum); High 0 mA.
Filament status (output)
8 outputs, active low, open collector, optically isolated. Low
= filament on.
Current: Low 10 mA (maximum)
VCE = 1.0 V (max) @ IC = 2 mA.
High 0 mA, V(max) = 30 Vdc.
Electrometer Input/Output
Coaxial inputs
Signal outputs
10 pA to 1 mA
0 to 9 Vdc
Logarithmic, -1 volt per decade of pressure. 9 V = 1
-9
-3
x 10 Torr...3 V = 1 x 10 Torr. (10/Torr gauge at 1
mA emission).
Electronic accuracy
± 3% of reading at 25 C ± 5 C (typical).
AC Line
4.0 A, slow blow, 250 V, 3 AG
Littelfuse, 313004
0.15 A, slow blow, 250 V, 3 AG, Littelfuse, 313.150
6 A, normal blow, 250 V, 3 AG, Littelfuse, 312006
10 A, slow blow, 250 V, 3 AG, Littelfuse, 313010
o
o
Fuses
Grid
Filaments
Degas
*Voltages referenced to analog ground.
Series 344
Granville-Phillips® Series 344
Vacuum Gauge Controller
This Instruction Manual is for use with Granville-Phillips
Series 344 Vacuum Gauge Controller.
Customer Service / Technical Support:
MKS Pressure and Vacuum Measurement Solutions
MKS Instruments, Inc., Granville-Phillips® Division
6450 Dry Creek Parkway
Longmont, Colorado 80503 USA
Tel: 303-652-4400
Fax: 303-652-2844
Email: [email protected]
MKS Corporate Headquarters
MKS Instruments, Inc.
2 Tech Drive, Suite 201
Andover, MA 01810 USA
Tel: 978-645-5500
Fax: 978-557-5100
Email: [email protected]
Instruction Manual
Instruction manual part number 344005
Revision C - November 2016