Product specifications

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DIFFERENTIAL PRESSURE
3
Capacitive Transducers
Setra’s capacitive pressure transducers are expertly de-
signed adaptations of a simple, durable and fundamen-
tally stable device...the electrical capacitor.
In a typical Setra conguration, a compact housing con-
tains two closely spaced, parallel, electrically isolated
metallic surfaces, one of which is essentially a diaphragm
capable of slight exing under pressure. The diaphragm
is constructed of a low-hysteresis material such as 17-4
PH SS or a proprietary compound of fused glass and
   

of the assembly, caused by a minute change in applied
      -
-
tance is detected by a sensitive linear comparator circuit
 
amplies and outputs a proportional, high level signal.
Capacitive RH Sensors
Setra’s Capacitive RH sensors consist of a ceramic sub-
strate on which a thin lm of polymer is deposited be-
tween two conductive electrodes. The sensing surface is
coated with a micro-pourous metal electrode, allowing
the polymer to absorb moisture while protecting it from
contamination and exposure to condensation. As the
polymer absorbs water, the dielectric constant changes
incrementally and is nearly directly proportional to the
relative humidity of the surrounding environment. Thus,
by monitoring the change in capacitance, relative hu-
midity can be derived. Setra’s patented charge balance
ASIC measures the capacitance change and uses digital
potentiometers to precisely calibrate the replaceable
sensor tip.
Inductive Current Sensors
Setra Current Switch and Transducers use inductive cur-
   -
mary conductor. The CT generates a low level AC cur-
rent which is proportional to the current owing in the
primary conductor. The resulting low level AC current
is rectied and compared to either a factory set or eld
-
ceeds the set point value, the internal circuitry triggers
the output switch to change state from open to short in a
current switch. The current transducers provide a DC out-
put with is linearly proportional to the sensed current.
.036 CU. IN
VOLUME
T
ypical capacitive pressure sensor, showing rugged
construction. Materials ar
e carefully selected for
compatibility to minimize envir
onmental effects.
(Capacitance gap is accentuated for illustration.)
Gold Plated
Surface
Ceramic
Wafer
Air
Dielectric
Diaphragm
(conductive
surface)
Sensor
Body
}
DIELECTRIC
CONDUCTIVE PLATES
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