Teledyne HASTINGS 2002, Instruction Manual, Page: 5 / 49

page 5
General Information
SECTION 1
The Model 2002 is a wide range vacuum measuring instrument consisting of a digital microproces-
sor-based display unit, a miniature, rugged, thin film based sensing element that measures from
below 1x10
-4
Torr up to 100 Torr with its matched EEPROM (Electrically Erasable/Programmable
Read Only Memory), a piezoresistive sensor that measures from 1 to 1000 Torr, and an intercon-
necting cable. Together, these components provide accurate vacuum measurement over 7 decades
of vacuum from 1x10
-4
Torr to 1000 Torr. This instrument is a new design approach based on
over 50 years of experience by Hastings Instruments with well-known and widely used thermal
conduction vacuum measurement techniques. The Model 2002 is designed for quick, easy installa-
tion and will provide the user with long lasting, trouble free, accurate vacuum measurement.
1.1 Features
• Wide dynamic range: 1x10
-4
to 1000 Torr
• Compact rugged design
• Attitude insensitive
• Fast dynamic response
• Withstands 150 psig positive pressure
• Linear per decade
• Bakeable to 250
0
C
• TTL output process control
• Interchangeable transducer
• Corrosion resistant
1.2 Model 2002 Sensors
The Model 2002 transducer is comprised of an ion implanted, piezoresistive, direct force sensor
and a thin film Pirani type sensor. The Pirani sensing element is a Pt thin film serpentine element
(see Figure 5.3a) deposited on a 1 micron thick Si
3
N
4
membrane. The membrane is peripherally
supported by a Si box shaped die and is covered by a thick Si lid parallel to the membrane and
open on two ends (see Figure 5.3b). The piezoresistive unit is an ion implanted Wheatstone bridge
in a 1 micron thick Si membrane peripherally supported by a Si box shaped die which has been
anodically bonded to a Pyrex substrate.
The dual sensor assembly is encased in a corrosion resistant 316 stainless steel tube shell. The
durable tube design withstands high pressure (150 psig/10.2bar), and high pressure surges. Since
the Pirani sensor is miniaturized and employs a Pt thin film on a Si
3
N
4
membrane (instead of a
conventional long fragile wire), the transducer can withstand high levels of mechanical shock.
The Model 2002 is designed for fast response. The micromachined sensing elements have a very
small mass and operate in a constant temperature (Pirani) and a constant current (piezo) feedback
mode. This makes response time very fast as compared to other commercially available sensors
which have to change the temperature of a significant mass to reflect pressure changes and have a
large internal volume which must equalize in pressure before the sensor can reach its final value.
Also, the transducer’s small internal volume (<1.5cc) permits rapid pneumatic response to system
pressure changes. Further, the small geometry of the transducer prevents thermal convection
currents which allows the sensor to be mounted in any orientation without calibration shifts.