Page 298 - Electromechanical Devices and Components Illustrated Sourcebook

260 Electromechanical Devices & Components Illustrated Sourcebook

Fixed Pivot which also drives the gauge needle. As pressure is applied to
Terminals the unit, the Borden tube tries to straighten out and activates
Pressure the gear mechanism that turns the needle and potentiometer.
Housing
Resistive The output of the potentiometer can drive either a voltage
Element divider or a Wheatstone bridge.
Lever Arm For more sensitive pressure readings, a bellows pressure
Pressure transducer is generally specified, as shown in Figure 15-48.
Port Wiper
Pressure is fed to the input and the bellows extends. The
opposite end of the bellows is connected to a linear poten-
Cam tiometer. As the pressure varies, so does the bellow’s length
and the position of the potentiometer. The output of the poten-
Diaphragm
tiometer can drive either a voltage divider or a Wheatstone
Figure 15-45 Diaphragm Pressure Transducer bridge.

Potentiometer
Gauge Housing Terminals Bellows Plunger Rod
Linear
Input Head
Potentiometer
Pressure
Needle 80 100 120
60 140 Input
Bezel 40 160
20 180 Bellows Weld
PSI 200 A B C Terminals
Moving Head
USA
Figure 15-48 Bellows Pressure Transducer
NPT Thread
Input
Figure 15-46 Commercial Pressure Gauge with 0- to 10-Volt
Output
A bellows-type pressure transducer can be constructed
using a spring return cylinder, as shown in Figure 15-49. The
output shaft of the cylinder is connected to the shaft of a lin-
Pressure transducers are also available in a pressure gauge ear potentiometer with a connecting nut. A cylinder arrange-
package, as shown in Figure 15-46. These units have princi- ment will not be as sensitive to minute changes as a bellows
pally the same appearance as a standard pressure gauge, because the piston and cylinder will exhibit a certain amount
except that they have an extended rear housing and three ter- of stiction.
minals. The rear housing accommodates a potentiometer ele-
ment. Information supplied by the manufacturer should be
used for wiring the transducer, although the center terminal is
Cylinder Rod
generally the wiper. Spring Return Plunger Rod
Cylinder Linear
Figure 15-47 shows the internals of a pressure gauge trans- Potentiometer
ducer. The mechanism is a standard Borden tube arrange-
ment. A potentiometer is added to the rear of the pinion gear,
Terminals
Pressure Input
Connector Nut
Jam Nuts
Figure 15-49 Cylinder Pressure Transducer
Case
Circular Rack
Pinion Gear
Differential Pressure Sensors
Toggle Link
Potentiometer
Face Differential pressure can be measured by arranging two bel-
Terminals Borden Tube lows sets and a linear potentiometer, as shown in Figure 15-50.
The output of the potentiometer drives a slide wire bridge.
Solder Joint The zero adjustment is used to zero the meter after the unit is
placed in service.
A differential pressure transducer can also be constructed
NPT Thread
using a pair of spring return cylinders, as shown in Figure 15-51.
Input The output shaft of the cylinders is connected to the shaft of
Figure 15-47 Pressure Gauge Transducer Internals a linear potentiometer with connecting nuts. As with the