What is a pressure transmitter?

What is a pressure transmitter?

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What is a pressure transmitter?

What is a pressure transmitter? A pressure transmitter or pressure sensor is a device that measures pressure in a liquid, fluid, or gas, or level of industrial liquids and gases.

Transmitter use to measure pressure in different processes.

Pressure transmitters are divided into three types:

Absolute Transmitter:

Absolute transmitter takes vacuum pressure as its base and then measures process pressure.

Gauge Transmitter:

This type measures process pressure with the location’s atmospheric pressure as a base.

Differential Transmitter:

When sensing units are introduced to multiple pressures as inputs, differential transmitters measure the differences between the various pressures.

Then it’s transducing that pressure into an analog electrical signal.

There are various types of pressure transducers, such as:

  • Pneumatic transmitter
  • Analog transmitter
  • Digital transmitter

Transducer

A transducer is a device which measures a physical quantity such as temperature or pressure and converts it into an electrical output signal.

What is the difference between transmitter and transducer

Both transducers and transmitters convert energy from one form to another and give an output signal. The signal is directed to any device that interprets it and uses it to display a record or alter the pressure in a system.

So how do you decide whether it is best to use a transducer or transmitter for your application? Transducers and transmitters are virtually the same things, the main difference being the kind of electrical signal each sends.

A transducer sends a signal in volts (V) or millivolt (mV) and a transmitter sends a signal in milliamps (mA).

If the electrical connections in your process are short, such as in the laboratory or inside an electronics enclosure, a pressure transducer is more desirable as they tend to be smaller and there are very few active electronic components that can be upset by electromagnetic interference.

HART®

HART or Highway Addressable Remote Transducer is a type of digital communications protocol for configuring and reading instrumentation via the 4 to 20mA current loop. HART® data is communicated via a low-level AC digital signal which is superimposed on a 2 wire 4-20mA current loop signal and functions simultaneously without interfering with the measurement output signal.

Bimetallic Thermometer

Bimetallic Thermometer

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Bimetallic Thermometer

In this article, we will introduce a Bimetallic Thermometer and how it dose work,also we will talk about the temperature & its application.

At the another part of the article will talk about the advantage of the bimetal and its sensors.
At the end of the article we will recommend to how to choose them and which factors is essential to choose the bimetal thermometers.

Thermometers are devices that measure temperature or a temperature gradient using a variety of different principles. Temperature is simply the numerical measurement of hot and cold—which has great importance in a wide variety of applications.

Temperature affects our comfort, cooks our food and is critical to making many products upon which we rely.

Given the extreme importance of temperature across so many aspects of modern life, thermometers are a familiar tool to us.

A thermometer is an instrument designed to measure and indicate the temperature of a specific application or condition. A bimetallic dial thermometer, commonly known as a bimetal thermometer, is installed at the point of measurement and is usually read from that location.

What is bimetal?

A bimetallic sensor is something that is made from two different types of metal joined together. Unlike many objects, bimetallic items are not made from a mixture of metals, but consist of layers of different metals.

Bi-metal is used for a variety of different reasons. Sometimes cheaper metals are covered with a thin layer of a more expensive metal so that the item looks expensive but has actually been made fairly cheaply.

Others, tin cans, for example, are made from steel that’s coated in a thin layer of a metal that won’t rust, to protect the steel from the elements.

It is possible to join three and four separate metals together; this is called tri-metal and tetra-metal.

Application of Bimetallic thermometer

  • use in control devices
  • use in air conditioning thermostats
  • process application such as refineries, oil burners, tire vulcanizers etc.

Advantages of bimetallic thermometers

They are simple, robust and inexpensive

Their accuracy is between +or- 2% to 5% of the scale

They can withstand 50% over a range in temperatures

They can be used where ever a mercury-in-glass thermometer is used

Limitations of a bimetallic thermometer

They are not recommended for temperature above 400’C

When regularly used, the bimetallic may permanently deform, which inturn will introduce errors

Different common forms of bimetallic sensors

  • Helix type
  • Spiral type
  • Cantilever type
  • Flat type

                                       

Choosing a thermometer

When selecting a thermometer, it is important to consider

  • the dial or case size
  • stem or capillary length
  • the connection type
  • temperature range

To ensure safety and accuracy, thermometers should be selected while giving consideration to the measured media and the ambient operating conditions.

Improper application may be detrimental to the thermometer, causing failure and possible personal injury or property damage.

Knowing the environment and media that the thermometer will be subjected to is also essential. This information will determine what type of thermometer is required and if thermowells are necessary.

Temperature measurement errors to keep in mind: conduction, convection, radiation, response time, noise, grounding issues and shorts (especially on metal surfaces).

Bimetal thermometer WIKA model 55 Bimetal thermometer WIKA model 55Bimetal thermometer WIKA model A43

 

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Unit of Temperature

Unit of Temperature

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Unit of Temperature

In this article, we introduce the Unit of Temperature and the method of converting each of these units to each other.

Many devices have been invented to accurately measure temperature. It all started with the establishment of a temperature scale. This scale transformed the measurement of temperature into meaningful numbers.

What is the temperature?

Temperature is a measure of the internal thermal energy state of a substance. It represents how much vibrational energy exists in the molecules of a liquid or solid, or the translational energy (speed of movement) of molecules in a gas.

Fahrenheit

The degree Fahrenheit ( o F) is the unit of temperature used by most people in the United States in describing weather.

The scale derives its name from a German-born physicist, Daniel Gabriel Fahrenheit, who is recognized as having invented it. At standard Earth-atmospheric sea-level pressure, pure water freezes at 32 o F and boils at +212 o F.

Celsius scale

The Celsius scale, previously known as the centigrade scale, is a temperature scale used by the International System of Units (SI).

As an SI derived unit, it is used by all countries except the United States, the Bahamas, Belize, the Cayman Islands, and Liberia.

It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale.

The degree Celsius (°C) can refer to a specific temperature on the Celsius scale or a unit to indicate a difference between two temperatures or uncertainty.

Before being renamed to honor Anders Celsius in 1948, the unit was called centigrade, from the Latin centum, which means 100, and grades, which means steps.

Kelvin Scale

The Kelvin Scale is a thermometric scale used in physical science to describe the absolute temperature of an object, substance, or area.

While Fahrenheit and Celsius scales measure temperature, the Kelvin Scale defines temperatures relative to an object’s thermodynamic movement.

As a result, the Kelvin Scale does not use degrees, but simply a number followed by “K” for Kelvin.

The Kelvin Scale begins at absolute zero (equivalent to -273.15° C), which is the temperature at which all objects stop moving, and ends at the triple point of water (equivalent to 0.01°C), which is the temperature at which water exists in all three states of matter simultaneously.

temperature unit conversion

 From Celsius to Fahrenheit

  • [°F] = [°C] ×9/5   + 32

From Fahrenheit to Celsius

  • [°C] = ([°F] − 32) ×5/9

From Celsius to Kelvin

  • [K] = [°C] + 273.15

From Kelvin to Celsius

  • [°C] = [K] − 273.15

From Kelvin to Fahrenheit

  • [°F] = [K] × 9/5   − 459.67

From Fahrenheit to Kelvin

  • [K] = ([°F] + 459.67) *5/9

Here you can to use temperature unit converter.

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Temperature

Temperature

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Temperature

Temperature measurement in today’s industrial environment encompasses a wide variety of needs and applications.

To meet this wide array of needs the process controls industry has developed a large number of sensors and devices to handle this demand.

Many methods have been developed for measuring temperature.

Temperature measurement can be classified into a few general categories:

  • Thermometers
  • Probes
  • Non-contact

Thermometers are the oldest of the group.

Thermometers

A thermometer is an instrument that measures temperature. It can measure the temperature of a solid such as food, a liquid such as water, or a gas such as air.

The three most common units of measurement for temperature are Celsius, Fahrenheit, and kelvin.

Bimetal Thermometer

Bimetallic thermometers are made up of bimetallic strips formed by joining two different metals having different thermal expansion coefficients.

Basically, bimetallic strip is a mechanical element which can sense temperature and transform it into a mechanical displacement.

This mechanical action from the bimetallic strip can be used to activate a switching mechanism for getting electronic output. Also it can be attached to the pointer of a measuring instrument or a position indicator.

Various techniques such as riveting, bolting, fastening can be used to bond two layers of diverse metals in a bimetallic strip.

How ever the most commonly used method is welding. Since two metals are employed to construct a bimetallic strip, hence the name.

Probes

Following the development of the thermometer, the next step in the evolution of temperature measurement was the development of the temperature probe. In 1826 an inventor named Becquerel used the first platinum-vs-palladium thermocouple.

Prior to this time all temperature measurement was done with liquid or gas filled thermometers. The invention of the thermocouple ushered in a whole new wave of development, culminating in what we know today as practical thermometry.

This resistance element was the first in a series of devices that are not classified as probes or transducers. These fall into three general categories:

  • Resistance elements
  • Thermopiles
  • Semiconductor

Resistance elements

Resistance elements were the first probes that came into being. Early inventors understood the relationship between temperature and the resistance of different elements. This gave rise to a series of elements called thermistors.

Thermistors

The thermistor is a device that changes its electrical resistance with temperature. In particular materials with predictable values of change are most desirable. The original thermistors were made of loops of resistance wire, but the typical thermistor in use today is a sintered semiconductor material that is capable of large changes in resistance for a small change in temperature.

RTD

The Resistance Temperature Detector (RTD) technically includes thermistor devices, however the term ‘RTD’ has come to stand for the specialized pure metal detector rather than the more generic semiconductor resistance element. These pure metal devices are highly accurate and stable over long periods of time.

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Types of pressure

Types of pressure

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Types of pressure

Pressure is an expression of force exerted on a surface per unit area. In this article, you found Types of pressure.

Gauge Pressure

The most common measurement of pressure is gauge pressure which is the pressure difference between the measured pressure and ambient pressure.

The term pressure is used if the measured pressure is higher than the atmospheric pressure. The term vacuum is used if the measured pressure is below atmospheric pressure.

The use of either of these terms automatically implies that the pressure (or vacuum) being measured is with respect to ambient pressure

(i.e. gauge pressure or vacuum).

In order to distinguish absolute pressure measurements, the words “absolute pressure” must be used.

Gauge Pressure uses a reference to the atmosphere around the sensor. Because the sensing element has a deflection due to a pressure change, a reference point is needed to know exactly what pressure is being measured.

Pressure sensors that use gauge pressure—typically seen in PSIG, BARG, and kPaG —have some type of vent.

This vent can be built into the sensor or even through a tube in the electrical connection. The vent is positioned to use atmospheric pressure as a reference point for the sensor to measure the media.

One common reason for using gauge pressure is to ensure that with any location throughout the world, the sensor will always reference the location in which it is installed.

Absolute Pressure

The most definite reference point is absolute zero pressure.

This is the pressure of empty space in the universe. When pressure is based on this reference point, it is called absolute pressure.

To distinguish it from other types of pressures it is accompanied by the suffix “a” or “abs” (from the Latin: absolutus = independent, separate from).

Absolute Pressure a perfect vacuum as its reference. This type of pressure reference is the gauge pressure of the media plus the pressure of the atmosphere.

As locations change, especially when dealing with elevation changes, the reference point can change because of atmospheric pressure differences.

Using an absolute pressure sensor eliminates the reference to a varying atmospheric pressure and relying on a specific pressure range for reference.

Differential pressure

Differential Pressure can be a little more complex than gauge or absolute but is simply measuring the difference between two media.

Although most gauge pressures are technically a differential pressure sensor—measuring the difference between the media and atmospheric pressure—a true differential pressure sensor is used to identify the difference between the two separate physical areas.

For example, the differential pressure is used to check the pressure drop—or loss—from one side of an object to the other.

The difference between the two pressures P1 and P2 is referred to as the pressure differential                ΔP = P1 – P2.

The difference between two independent pressures is called the differential pressure

Atmospheric pressure

The most important pressure for life on earth is atmospheric air pressure pamb (amb = ambient, surrounding).

It is produced by the weight of the atmosphere surrounding the earth up to an altitude of about 300 miles.

Atmospheric pressure decreases continuously up to this altitude until it practically equals zero (full vacuum).

Atmospheric air pressure undergoes climatic changes, as shown by the daily weather report.

At sea level, pamb has an average value of 29.90 inches of Mercury (“Hg). In high or low-pressure weather zones it can fluctuate by as much as ± 5%.

 Five main units of pressure

The unit of pressure in the SI system is the pascal (Pa), defined as a force of oneNewton per square meter. The conversion between atm, Pa, and torr is as follows: 1 atm = 101325 Pa = 760 torr.

 

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Pressure

What is Pressure?

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What is Pressure?

What is pressure ? pressure is defined as force per unit area.

At first, we explain the concept of Pressure in Science, Physics, and Chemistry.

Pressure, in the physical sciences, the perpendicular force per unit area, or the stress at a point within a confined fluid. … In SI units, the pressure is measured in pascals; one pascal equals one newton per square meter. Atmospheric pressure is close to 100,000 pascals.

PRESSURE is a force exerted by the substance per unit area on another substance. The pressure of a gas is the force that the gas exerts on the walls of its container.

In other words, The rapid motion and collisions of molecules with the walls of the container causes pressure (force on a unit area). Pressure is proportional to the number of molecular collisions and the force of the collisions in a particular area.
The more collisions of gas molecules with the walls, the higher the pressure.

pressure

 

So to create a large amount of pressure, you can either exert a large force or exert a force over a small area (or do both).

This force can be exerted by liquids, by gases or vapors, or by solid bodies.
Surface compression takes place at the interface between two solid bodies, but for our purposes, we can consider this additional force negligible.

Common Units of Pressure

There are three general classifications for units of  measurement as follows:

Customary (inch, pound force, second, ampere)- used primarily in English speaking countries, but in many countries are being replaced by SI units. Customary units of pressure include PSI, in. Hg, in.H2O.

 

SI – (meter, Newton, second, ampere) – Commonly used in Europe and now popularly known as “metric” units. SI units of pressure include bar, mbar, Pa, kPa, MPa, and N/m2.

MKSA (meter, kilogram-force, second, ampere) – formerly known as “metric” units but are generally

being replaced by SI units. MKSA units of press include kg/cm2, mH2O, mmHg, and torr.

In meteorology, an atmosphere equals 14.7 pounds per square inch or 101.325 kilopascals.

Fluid Pressure

The press exerted by a static fluid depends only upon the depth of the fluid, the density of the fluid, and the acceleration of gravity.

The pressure in a static fluid arises from the weight of the fluid and is given by the expression

fluid pressure

Pstatic fluid = ρgh where ρ = m/V = fluid density
g = acceleration of gravity
h = depth of fluid

 

When a fluid is at rest, it exerts a force perpendicular to any surface in contact with it. This force, which is due to the continuous, random motion of molecules, is known as fluid press. Knowing the fluid pressure is essential to mechanical and hydraulic systems that use fluids move pistons and other parts.
It is usually measured in Pascals (Pa), where one Pascal is equal to one Newton per square meter (N/m2).

The fluid press is independent of the mass of the fluid but can be calculated with the density and height of the fluid.

Because of the ease of visualizing a column height of a known liquid, it has become common practice to state all kinds of pressures in column height units, like mmHg or cm H2O, etc. Press is often measured by manometers in terms of liquid column height.

Definition of Gas Press

When the molecules of gas bounce off the walls of their container, they exert a force.

The gas press is defined as the force per unit area produced by the gas. Depending on the purpose of the measurement, different units are commonly used.

The pressure gauge is an instrument that can measure the pressure of the media.
Many kinds of pressure gauges are in the industry and we can choose them according to many factors that we will talk about them in the next articles.

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