Pressure gauges and switches are among the most often used instruments
in a plant. But because of their great numbers, attention to
maintenance--and reliability--can be compromised. As a consequence, it
is not uncommon in older plants to see many gauges and switches out of
service. This is unfortunate because, if a plant is operated with a
failed pressure switch, the safety of the plant may be compromised.
Conversely, if a plant can operate safely while a gauge is defective, it
shows that the gauge was not needed in the first place. Therefore, one
goal of good process instrumentation design is to install fewer but more
useful and more reliable pressure gauges and switches.
One way to reduce the number of gauges in a plant is to stop installing
them on the basis of habit (such as placing a pressure gauge on the
discharge of every pump). Instead, review the need for each device
individually. During the review one should ask: "What will I do with the
reading of this gauge?" and install one only if there is a logical
answer to the question. If a gauge only indicates that a pump is
running, it is not needed, since one can hear and see that. If the gauge
indicates the pressure (or pressure drop) in the process, that
information is valuable only if one can do something about it (like
cleaning a filter); otherwise it is useless. If one approaches the
specification of pressure gauges with this mentality, the number of
gauges used will be reduced. If a plant uses fewer, better gauges,
reliability will increase.
Part NO: 200.02.003.fl106
Pressure Gauge
- PRESSURE GAUGE
Dial size of Pressure Gauge : 40, 50, 63, 100, 150, 200, 250mm
Case : Pressed steel or stainless Steel
Mounting : Surface, Direct, Back or Panel
Range : 760mm Hg to 0 vaccum, 0 to 700Kg/cm² Comp-760mm Hg to 28 Kg/cm2 or Bar & Psi Scales.
Working parts : Non ferrous
Connections : 1/8", 1/4", 3/8" ,1/2" BSP, NPT, OR Metric Threads
ACCURACY : +/- 2% FSD
Note : Glycerine filled on request. Ammonia &
Oxygen Gauges also avaliable.
- PRESSURE
SWITCH
Temperature Limits: -40°F to 140°F (-40°C to 60°C). 0°F to 140°F
(-18°C to 60°C) for 1950P-8, -15, -25, and -50. -30°F to 130°F for
1950-02
Maximum Surge Pressure: 1950 - 10 PSI (.7 bar), 1950P - 50 PSI (3.4
bar), 1950P-50 only - 90 PSI (6.2 bar) Rated Pressure: 1950 - 45" (.1 bar) w.c.,
1950P - 35 PSI (2.4 bar), 1950P-50 only - 70 PSI (4.8 bar)
Pressure Connections: 1/8" NPT(F). Electrical Rating: 15 amps, 125, 250, 480 volts, 60 Hz. A.C.
Resistive 1/8 H.P. @ 125 volts, ¼ H.P. @ 250 volts, 60 Hz. A.C. Wiring Connections: 3 screw type; common, norm. open and norm.
closed.
Conduit Connection: ½" NPT(F). Set Point Adjustment: Screw type on top of housing. Field
adjustable.
Housing: Anodized cast aluminum. Diaphragm: Molded fluorosilicone rubber. 02 model, silicone on
nylon. Calibration Spring: Stainless steel. Installation: Mount with diaphragm in vertical position. Weight: 3¼ lbs (1.5 kg). 02 model, 4 lbs., 7 oz. (2 kg)
Part NO: 200.02.003.fl107
Pressure Switch
PRESSURE SENSORS
Pressure sensors include all sensors,
transducers and elements that produce an electrical signal proportional
to pressure or changes in pressure. Pressure sensors are devices that
read changes in pressure, and relay this data to recorders or switches.
They are commonly used in safety devices such as safety mats, edges and
bumpers to actuate shut-off switches. Other pressure devices include
transducers, transmitters, elements, indicators, gauges (bellows,
bourdon tubes, capsule elements and diaphragm elements) and controllers.
There are five main pressure sensor types: absolute, gauge, vacuum,
differential and sealed. Each of these sensors measures different
pressure variables. The first of these sensor types are absolute
sensors. These devices test for absolute pressure, which is a
measurement of pressure, relative to a perfect vacuum. Gauge sensors are
the most common type of pressure sensors. They can be calibrated to
measure pressure with respect to atmospheric pressure at a given
location. Vacuum sensors are used in situations where the pressure level
that is being tested for, is lower than the localized atmospheric
pressure. Differential pressure is measured by reading the difference
between the input of two or more pressure levels. Finally, sealed gauged
sensors measure pressure relative to one atmosphere at sea level (14.7
PSI) regardless of local atmospheric pressure.
There are numerous technologies by which pressure transducers and
sensors function. Some of the most widely used technologies include
piston technology, mechanical deflection, strain gauge, semiconductor
piezoresistive, piezoelectric (including dynamic and quasistatic
measurement), microelectromechanical systems (MEMS), vibrating elements
(silicon resonance, for example), and variable capacitance.
Other variations within pressure sensors include their manners of
receiving and displaying data. Many of these sensors are geared to
provide out in analog form, either current, voltage, or AM / FM signals.
Other methods include switch / alarm outputs, parallel or serial output
to sensor systems or industrial computers, or, in some advanced pressure
sensor models, digital or video displays.
