DEFINING
A NEW GENERATION OF PRESSURE STANDARDS
The pressure balances fundamental operating principle and excellent long-term
stability have made it an indispensable tool in high accuracy pressure metrology.
As accuracy levels increase, quality assurance requirements intensify and
automation spreads through the work-place, the pressure balance must evolve
to continue to fill its essential role in the measurement system. The PG7601
pressure calibration system - by the thorough application of new technology
combined with the refinement of traditional techniques - has been designed
from the ground up to meet this challenge.
A new family of large diameter piston-cylinders. A high purity ceramic
material is used for the low-pressure pistons to reduce weight and improve
performance. New proprietary lapping techniques achieve geometry within
0.1 micron of ideal and radial clearances of less than one micron. The
combination of excellent geometry, small annulus and large diameter
minimises possible gas species and operating mode effects.
The piston-cylinder mounting system is simplified to eliminate all
parasitic sources of stress and to allow the piston-cylinder and its
mounting sleeve to be mounted as a single assembly in a simple one-step
procedure without exposing critical piston-cylinder surfaces.
An automated piston rotation system operates "as needed"
to maintain optimum rotation speed without interfering with piston position
or movement. The operator is alerted prior to engagement.
The vacuum reference is contained under a one-piece bell jar, all
metallic surfaces exposed to vacuum are electropolish finished low carbon
stainless steel, and large diameter (KF25) vacuum connections are used
to ensure rapid evacuation and lower ultimate pressures. Piston position
and rotation rates are detected by non-interfering LVDT and optical
sensors.
Power supplies and displays are mounted in the PG Terminal remote
from the pressure balance platform to avoid on-board heat sources and
thermal instability.
MEASURING
AND ACCOUNTING FOR ALL SYSTEM VARIABLES. REAL TIME
The pressure defined by a high accuracy pressure balance is affected by
many environmental and system variables. In the past, the technical and
practical difficulties of accurately obtaining values and calculating for
all of the significant variables led to certain parameters being assumed
to be constant or ignored completely. Though this may have been acceptable
at the +100 ppm accuracy level, to assure accuracy of +50 ppm or better
it is indispensable that all of the parameters are accurately accounted
for. PG7601 does this systematically.
On-board PG7601 sensors continuously measure ambient pressure, temperature
and humidity, vacuum reference, piston-cylinder temperature and piston behaviour.
Using these real time measurements and extensive stored information, embedded
software applies the complete pressure equation and delivers fully validated
pressure to mass or mass to pressure data - every 2 seconds.
REMOVING
OPERATOR INFLUENCE FROM THE MEASUREMENT PROCESS
The PG7601's automated control features and extensive on-board measurement
and analysis capabilities are used to remove the influences of operator
technique and judgment on measurement results. The operator interacts with
the system through the PG Terminal's keypad and display. After entering
the desired pressure, the system prompts for the mass value to be loaded.
Once the operator confirms that the mass has been loaded, the PG7601 system
takes over executing all the necessary functions to float and rotate the
piston, evaluate operating conditions and provide a "ready" indication
when all necessary conditions for in-tolerance measurements are met.
Automated functions and objective system criteria rather than operator
technique and subjective judgment assure, among other things, that the
vacuum reference
is adequate, that pressures are set in a repeatable manner, and that piston
rotation speed and fall rate are within limits. On-board diagnostics assist
the operator in troubleshooting when ready conditions cannot be achieved.
For example, excessive decay in piston rotation speed may indicate an
unclean
piston-cylinder or an excessive fall rate implies a leak in the test system.
Manual override capability of all functions is also available to bypass
automated control when desired.
Finally, COMPASS 7601
computer software is available
to interact with the system and step the operator through complete automated
calibration routines, record test results in data files and edit and print
calibration certificates.
PUTTING
TOGETHER A SYSTEM
A PG7601 system is made up of components ordered separately to tailor a
system to your specific requirements. PG7601 system components include:
The PG7601 pressure balance platform with the PG Terminal.
The mass set.
Piston-cylinder(s). One to three assemblies depending on the pressure
ranges desired.
A pressure generation and control component for manual or automated
operation.
System configuration accessories: interconnecting hardware, vacuum
pumps.
Calibration assistance software.
Pressure
Balance Platform with Terminal Part Number: PG7601 Purpose: The PG7601 platform is designed for mounting of the
piston-cylinder assembly, rotating the piston, applying pressure beneath
it and establishing a vacuum reference around the mass load. It includes
on-board electronic sensors, signal conditioning and logic for determination
of all ambient and piston-cylinder behaviour variables and computation
of fully compensated pressure to mass and mass to pressure values.
The PG Terminal is a miniature console unit that contains the platform's
power supplies and provides a keypad and display for simple local
user access to all system functions. System functions can also be
accessed by simple ASCII commands over the included RS232 port and
IEEE 488 interface.
Ordering description: PG7601 gas operated pressure balance
complete with PG Terminal, mass carrying bell, bell jar, IEEE 488
and RS232 interfaces, spare wear subjected parts kit, accessories,
user's manual, technical data, reusable storage and transport case.
Mass
Set Part Number: MS-7601 -35 Purpose: Applies the load to the piston-cylinder as needed
to achieve the desired pressure increment. Mass set composition allows
any load between 200g and 35kg to be loaded within 10 mg.
Ordering description: 35kg mass set complete with trim masses,
mass tray, dust cover, calibration certificate, two reusable storage
and transport cases.
Piston
Cylinders Part Numbers:
PC-7600-10 [5 to 350 kPa (0.7 to 50 psi)]
PC-7600-50 [25 to 1750 kPa (3.5 to 250 psi)]
PC-7600-200 [100 to 7000 kPa (14.5 to 1000 psi)]
Purpose: The basic metrological element that determines the
pressure range. The final digits in the identifier specify the nominal
Kn mass to pressure conversion coefficient in kPa/kg. The resulting
ranges are from 0.5 x Kn to 35 x Kn corresponding to the minimum and
maximum mass loads. The PG7601 mass set composition allows pressures
to be defined in any engineering unit.
Ordering description: Kn = 10 (or 50 or 200) kPa/kg piston-cylinder
assembly complete with retaining sleeve, calibration certificate,
reusable storage and transport case.
Pressure
Generation And Control Component Automated Pressure Controller Part Number: PPC1 -1000 Purpose: Controlled by the PG7601 to provide automated pressure
setting in the system and to automatically float and maintain piston
position. Automated function can be overridden and pressure controlled
by front panel push buttons or optional joystick when desired.
Ordering description: Positive shut-off pressure controller
complete with power cord and user's manual.
Manual Pressure Controller Part Number: MPC1-1000 Purpose: Provides manual pressure control to set pressure in
the system and float and maintain piston position. Ordering description: Manual pressure controller complete with
user's manual.
System
Configuration Accessories Pneumatic Interconnections Kit With Test Connection Part Number: PK-7601 -PPC/MPC Purpose: Completes the pneumatic circuit of a PG7601 system
by providing pneumatic interconnections between the PG 7601, an MPC1
or PPC1, and a test connection. The test connection is a quick connector
on a mounting stand. Ordering description: Interconnections kit for a PG7601 /PPC1
/MPC1 system including quick connection to test with 1/8"NPTF,
and 37 degree flare quick connectors.
Vacuum Kit For Pressure Controller Part Number: VA-PPC/MPC-REF Purpose: Connects to PPC1 or MPC1 to provide vacuum capability
for setting pressures under atmosphere. Needed only if the system
will be used to define absolute pressures under atmospheric pressure.
Ordering description: Vacuum package for PPC1 /MPC1 with interconnecting
hardware, vacuum pump and instruction sheet.
Vacuum Kit For PG 7601 Platform Reference Part Number: VA-7601 -REF Purpose: Connects to PG7601 reference vacuum port to evacuate
the PG7601 bell jar. Needed only if the system will be used to define
absolute pressures with a vacuum reference. Ordering description: Vacuum package for PG7601 reference with
interconnecting hardware, vacuum pump and instruction sheet.
High Accuracy Barometer Part Number: RPM1 -A0015 Purpose: Interface with PG7601 to provide atmospheric pressure
measurements with higher accuracy than the PG7601's internal sensor.
Recommended for making absolute pressure measurements above atmospheric
pressure without using a vacuum reference and for negative gauge pressures
and gauge pressures very near atmospheric pressure. Ordering description: RPM1 -A0015 reference pressure monitor
complete with utility software, RS232 cable, calibration certificate,
power cord and manual.
Calibration
Assistance Software Part Number:COMPASS®7601 Purpose: Standard personal computer software interacts with
system to automate complete calibration routines, log test results
in data files and edit and print calibration certificates. Ordering description: Calibration software with user's manual.
Pressure range: 5 to 350 kPa (0.7 to 50 psi)
Nominal diameter: 35 mm
Nominal area: 10 cm2
Material: Ceramic piston in tungsten carbide cylinder
Nominal piston mass with head: 200 g
Fall rate; Min. float time: 0.2 mm/min max., 25 min.
Range 2, Kn = 50 kPa/kg
Pressure range: 25 to 1750 kPa (3.5 to 250 psi)
Nominal diameter: 1 6 mm
Nominal area: 2 cm2
Material: Ceramic piston in tungsten carbide cylinder
Nominal piston mass with head: 200 g
Fall rate; Mm. float time: 0.5 mm/min max., 10 min.
Range 3, Kn = 200 kPa/kg
Pressure range: 100 to 7000 kPa (14.5 to 1000 psi)
Nominal diameter: 8 mm
Nominal area: 0.5 cm2
Material: Piston and cylinder in tungsten carbide
Nominal piston mass: 200 g
Fall rate; Min. float time: 1 mm/min max., 5 min
Mass set
Nominal total mass:
35kg
Composition:
1 x 4.5 kg
5 x 5 kg
2 x 2 kg
1 x 1 kg
1 x 0.5 kg
2 x 0.2 kg
1 x 0.1 kg
Trim mass set from 50 g to 10 mg
Mass type:
5 to 1 kg: solid.
500 g to 100 g: adjustable
50 g to 10 mg: NIST S1
Material:
AISI 304L non-magnetic stainless
steel
Finish:
Electropolished
Adjustment tolerance:
±20 ppm of nominal value
Accuracy of reported values:
± 5 ppm
Pressure
Measurements
Accuracy in gauge and absolute modes using nitrogen, helium or air.
Uncertainties are calculated using 2 sigma, root sum squared techniques
as recommended in lSO/TAG4/WG3. Reported values are directly traceable
to NIST. Note that current absolute accuracy is limited by the uncertainty
on the reference values available for calibration, not by the intrinsic
performance of the PG7601, so higher accuracies are possible when
improvements in reference values occur.
Range 1
±20 ppm
Range 2
±35 ppm
Range 3
±50 ppm
System
Temperature
Operation:
10 to 40°C
Storage:
-25 to 85°C
Power
requirements
85 to 264
VAC, 47 to 440 Hz, 22VA max
Communication
ports
IEEE-488:
for communication with a host
computer
(3) RS232
ports
COM1: for
communication with a host computer
COM2: for communication with RPM high accuracy barometer
COM3: for communication with PPC pressure controller
PG terminal:
serial and power lines
On-board
measurements
- Temperature
(internal)
Range:
0 to 40°C
Resolution:
0.01 °C
Accuracy:
±0.1°C
-Temperature
(external)
Range:
0 to 40°C
Resolution:
0.1 °C
Accuracy:
±1 °C
-Atmospheric
pressure
Range:
70 to 110kPa
Resolution:
10 Pa
Accuracy:
±0.2% of reading
-Vacuum
Range:
0 to 20 Pa
Resolution:
0.01 Pa
Accuracy:
± 0.1 Pa or 10% whichever
is greater
-Humidity
Range:
5 to 95% RH
Resolution:
1%
Accuracy:
±10%
-Piston position
Piston stroke:
+4.5 mm
Resolution:
0.01 mm
Accuracy:
±0.2 mm
Piston
rotation system
Automated
with override capability. Operates "as needed" To
maintain rotation rate within defined limits. "Not ready"
indicated when rotation system is engaged
Pressure
control
Automated (PPC1)
or manual (MPC1)
Processors
Platform:
Motorola 68302.
Terminal:
Hitachi 64180
On-board
data handling
Continuous
calculation of mass to pressure or pressure to mass from piston-cylinder
and mass set file information and real time measurement of operating
conditions.
Continuous ready/not ready indication.
Diagnosis of non-ready condition
Supported
test gases:
Nitrogen, Helium,
and Air
Due to a
policy of continuous improvement all specifications are subject to
change without notice.
