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HPM-2002-OBEVacuum Gauge Page 5 of 39
1. General Information
The Hastings HPM-2002-OBE is a small, low cost electronics module which provides the user with
accurate vacuum measurements over a wide range of pressure. The HPM-2002-OBE uses the same rugged
HPM-2002s transducer tube as the HPM-2002 bench top instrument. This tube features two sensors; a
patented thin-film Pirani sensor and a piezoresistive sensor combined in a single tube with a matched EEPROM
(Electrically Erasable/Programmable Read Only Memory).
The HPM-2002-OBE electronics module combined with the HPM-2002’s tube provides accurate vacuum
measurement from 1x10
-4
Torr to 1000 Torr. The HPM-2002-OBE is designed for quick, easy installation and
will provide the user with long lasting, trouble free, reliable vacuum measurement.
1.1. Features:
• Low-Cost Electronics Module
• Wide Dynamic Range 1x10
-4
Torr to 1000 Torr
• Combined Sensors in a Single Tube
• Input Voltage (11.5-30 VDC)
• Connector: 15-pin high-density male “D”
• Optional 4-digit LED Display
• Optional Outputs (Dual 0-10 volt analog or RS232/485)
1.2. Model 2002 Sensors
The Model 2002 transducer tube 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 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. 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 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 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 (<1.5 cc) 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.
1.3. HPM-2002-OBE Analog Output Module
The analog output (0-10 V) module consists of a power conversion/sensor transducer board,
microprocessor board and a user interface option board. Two 0-10 Volt linear outputs are generated for the user
via the high-density 15-pin “D” connector. The first of these outputs covers the pressure range from 0 to 1024
Torr. The second output covers the range from 0 to 1000 mTorr. A four digit floating-point LED display is
standard.
1.4. HPM-2002-OBE Analog Output (4-20mA) Module
(Identical to 1.3, except replace 0-10 V with 4-20 mA)