CHAPTER 3
TELEVAC
Principles of Operation
2A Thermocouple Sensor
The 2A thermocouple sensor tube consists of a
metal shell containing fine wire filaments of
dissimilar metals, which form a thermocouple.
The thermocouple sensor measures absolute
pressures by determining the temperature of a
thermocouple junction as the surrounding
pressure changes. The response of the sensor
depends on the gas pressure and type.
The range of these sensors is from 1 millitorr to
20,000 millitorr (10-3 Torr to 20 Torr). The
sensor housing is constructed of stainless steel or
alternately nickel plated brass. Both are capable
of withstanding 150 psi overpressure.
Figure 3
2A Thermocouple Sensor Tube
Figure 4
4A Convection Sensor Tube
Convection Sensor
The convection sensor measures absolute pressures
by determining the heat loss from a thermocouple
heated to a constant temperature by a current source.
A second thermocouple compensates for ambient
temperature changes and extends the vacuum
measurement range above 2 Torr by measuring the
convection effects. The range of these sensors is 1
millitorr to 1000 Torr
The convection sensor must be mounted vertically
for accurate measurements. Sensors are available in
Stainless Steel or Nickel plated Brass and can
withstand 150-psi overpressure.
Phone:(215) 947-2500 fax:(215) 947-7464 e-mail: [email protected] web site:www.televac.com
6-8000-002 REV A
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