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149-072011 Model 2002 Vacuum Gauge Page 4 of 38
1. General Information
The Model 2002 is a wide range vacuum measuring instrument consisting of a digital microprocessor-based
display unit, a miniature, rugged, thin film based sensing element that measures from below 1x10-4 up to
100 Torr, a piezoresistive sensor that measures from 1 to 1000 Torr, EEPROM (Electrically
Erasable/Programmable Read Only Memory), and an interconnecting cable. Together, these components
provide accurate vacuum measurement over 7 decades of vacuum from 1x10-4 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 installation 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 2500C
• 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 Si3N4 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 50 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/10.2 bar) and high pressure surges. Since the Pirani sensor is
miniaturized and employs a Pt thin film on a Si3N4 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 micro machined 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 with the system before the sensor can reach its final value. The transducer’s small
internal volume (<1.5cc) permits rapid pneumatic response to system pressure changes. Further, the small
geometry of the transducer prevents a thermal convection current which allows the sensor to be mounted in
any orientation without calibration shifts.
1.3. Model 2002 Control Unit
The Model 2002 control unit consists of the power supply, Pirani resistance bridge control, signal processing
and display circuitry. The user interface consists of a flat panel display with smooth operating tactile
switches and large green LED digits (0.56"/14.2mm). The pressure is displayed in scientific format using a 3
digit mantissa and a 1 digit (plus the sign) exponent. The pressure can be displayed in Torr, mbar or Pascal.
The instrument comes standard with 2 alarm setpoints that have TTL level digital outputs. An optional dual
relay board can be internally mounted to trip on the alarm setpoints to turn on/off various equipment such as
pumps, valves, heaters, bake out ovens and safety equipment. An optional 4-20 mA or 0-10V analog output