A pressure sensor measures pressure

8/7/2019 A pressure sensor measures pressure

http://slidepdf.com/reader/full/a-pressure-sensor-measures-pressure 1/12

Pressure Transducer:

In this project we want to glow the street light from happening pressure on road breaker bymotor cycle or four wheeler.

We used pressure sensor for sensing the pressure and we convert it into light energy and

measure the pressure on galvanometer.

Block Diagram:

A pressure sensor measures pressure, typically of gases or liquids. Pressure is an expression

of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer ; it generates a signal as a function of

the pressure imposed. For the purposes of this article, such a signal is electrical.

Pressure sensors are used for control and monitoring in thousands of everyday applications.

Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow,

speed, water level, and altitude. Pressure sensors can alternatively be called pressure

transducers, pressure transmitters, pressure senders, pressure indicators and

piezometers, manometers, among other names.

Pressure sensors can vary drastically in technology, design, performance, application

suitability and cost. A conservative estimate would be that there may be over 50 technologiesand at least 300 companies making pressure sensors worldwide.

There is also a category of pressure sensors that are designed to measure in a dynamic mode

for capturing very high speed changes in pressure. Example applications for this type of sensor would be in the measuring of combustion pressure in an engine cylinder or in a gas

turbine. These sensors are commonly manufactured out of piezoelectric materials such as

quartz.

Pressure Sensors Amplifier A Amplifier B

Optocopler (MCT2E) ULN2803 High

Current Driver IC

Relay For Switching

the Street Light

Load



Some pressure sensors, such as those found in sometraff ic enforcement cameras, function ina binary (on/off) manner, i e., when pressure is applied to a pressure sensor, the sensor acts to

complete or break an electr ical circuit. These types of sensors are also known as a pressureswitch.

There are many applications for pressure sensors:

y Pressure sensing

This is the direct use of pressure sensors to measure pressure. This is useful in weather

instrumentation, aircraf t, cars, and any other machinery that has pressure functionality

implemented.

y Al i ude sensing

This is useful in aircraf t, rockets, satellites, weather balloons, and many other applications.

All these applications make use of the relationshi p between changes in pressure relati e to the

altitude. This relationshi p is governed by the following equation[1]:

This equation is cali brated for analtimeter , up to 36,090 feet (11,000 m). Outside that range,

an error will be introduced which can be calculated differently for each different pressure

sensor. These error calculations will factor in the error introduced by the change in

temperature as we go up.

Barometr ic pressure sensors can have an a ltitude resolution of less than 1meter, which is

signif icantly better than GPS systems (about 20 meters altitude resolution). In navigationapplications altimeters are used to distinguish between stacked road levels for car navigation

and f loor levels in buildings for pedestr ian navigation.

y Fl w sensing

This is the use of pressure sensors in con junction with theventur i effect to measure f low.

Differential pressure is measured between two segments of a ventur i tube that have adifferent aper ture. The pressure difference between the two segments is directly propor tional

to the f low rate through the ventur i tube. A low pressure sensor is almost always required asthe pressure difference is relatively small.

y Level / depth sensing

A pressure sensor may also be used to calculate the level of a f luid. This technique iscommonly employed to measure the depth of a submerged body (such as a diver or submar ine), or level of contents in a tank (such as in a water tower). For most practical

purposes, f luid level is directly propor tional to pressure. In the case of fresh water where thecontents are under atmospher ic pressure, 1psi = 27.7 inH20 / 1Pa = 9.81 mmH20. The basic

equation for such a measurement is



where P = pressure, p = density of the fluid, g = standard gravity, h = height of fluid columnabove pressure sensor

y Leak testing

A pressure sensor may be used to sense the decay of pressure due to a system leak. This is

commonly done by either comparison to a known leak using differential pressure, or bymeans of utilizing the pressure sensor to measure pressure change over time.

LM358 Operational Amplifier:

LM358-The LM358 series consists of two independent, high

gains,internally Frequency compensated operational amplifierswhichwere designed specifically to operate from a single power supplyover a wide range of voltages.Operation from split power supplies is alsopossible and the low power supply current drain is independent of themagnitude of the powersupply voltage. Application areas include transducer amplifiers, dc gain blocks and allthe conventional op amp circuits which now can be more easilyimplemented in single power supply systems.For example, the LM158series can be directly operated off of the standard +5V power supplyvoltage which is used in digital systems and will easily provide the

required interface electronics without requiring the additional ±15V .

PIN -



MCT2E Optocoupler:

Optocouplers

Optocouplers were discovered right after photo-transistors (like any other transistor,except it is stimulated by light), by combining a LED and photo -transistor in the samecase. The purpose of an optocoupler is to separate two parts of a circuit.

This is done for a number of reasons:

y Interference . Typical examples are industrial units with lots of interferences whichaffect signals in the wires. If these interferences affected the function of controlsection, errors would occur and the unit would stop working.



y Simultaneous separation and intensification of a signal . Typical examples are relays

which require higher current than microcontroller pin can provide. Usually,optocoupler is used for separating microcontroller supply and relay supply.

y In case of a breakdown, optocoupled part of device stays safe in its casing, reducingthe repair costs.

Optocouplers can be used as either input or output devices. They can haveadditional functions such as intensification of a signal or Schmitt triggering (theoutput of a Schmitt trigger is either 0 or 1 - it changes slow rising and fallingwaveforms into definite low or high values). Optocouplers come as a single unit or ingroups of two or more in one casing.

Each optocoupler needs two supplies in order to function. They can be used withone supply, but the voltage isolation feature, which is their primary purpose, is lost.

Connecting the optocoupler and relay to a microcontroller

A relay can also be activated via an optocoupler which at the same time amplifie s

the current related to the output of the microcontroller and provides a high degree of isolation. High current optocouplers usually contain a 'Darlington' output transistor toprovide high output current.

Connecting via an optocoupler is recommended espe cially for microcontroller applications, where relays are used fro starting high power load, such as motors or heaters, whose voltage instability can put the microcontroller at risk. In our example,when LED is activated on some of the output port pins, th e relay is started. Below isthe program needed to activate the relay, and includes some of the alreadydiscussed macros.

Relay Circuit employing optocoupler



Relay:





y Armature that can be attracted by the electromagnet y Spring y Set of electrical contact

The following figure shows these four parts in action:

In this figure, you can see that a relay consists of two separate and completely independent

circuit . The first is at the bottom and drives the electromagnet. In this circuit, a switch is

controlling power to the electromagnet. When the switch is on, the electromagnet is on, and

it attracts the armature (blue). The armature is acting as a switch in the second circuit. When

the electromagnet is energi ed, the armature completes the second circuit and the light ison. When the electromagnet is not energi ed, the spring pulls the armature away and the

circuit is not complete. In that case, the light is dark.

When you purchase relays, you generally hav e control over several variables:

The voltage and current that is needed to activate the armature

y The maximum voltage and current that can run through the armature and thearmature contacts

y The number of armatures (generally one or two)y The number of contacts for the armature (generally one or two -- the relay shown

here has two, one of which is unused)



y Whether the contact (if only one contact is provided) is normally open (NO) or

normally closed (NC)



ULN2 0 :

The 2 A i hi h-volt e, hi h-current r lington transistor array. The evice consists of eight npn ar lington pairs that f eature high-voltage outputs ith common-cathode clamp diodes f or switching inductive loads. The collector-current rating of each ar lington pair is m A. The ar lington pairs may e connected in parallel f or

higher current capability.

Applications include relay dr ivers, hammer dr ivers, lamp dr ivers, display dr ivers Eand gas discharge), line dr ivers, and logic buff ers. The 2 A has a 2.7 -

k�ser ies base resistor f or each ar lington pair f or operation directly with TTL or -VS devices.

Galvanometer

A galvanometer is a type of ammeter : an instrument f or detecting and

measur ing electr ic current. It is an analog electromechanical transducer that

produces a rotary deflection of some type of pointer in response to electr ic

current flowing through its coil. The term has expanded to include uses of the same

mechanism in recording, positioning, and servomechanism equipment.



Wein Bridge Circuits:

Schematic Diagram:



PCB Layout:

Documents

A pressure sensor measures pressure