Pressure Transducers

What is Transducer?

Each electric circuit or system needs to communicate with the real world to perform its task. This communication often takes place through devices such as a transducer. A transducer is an instrument which is used to convert physical quantities to electrical ones. For example, it converts the physical quantity to voltage or electric current. In other words, it changes the quantities to the form, which is measurable in the form of electrical signals. The primary quantity may be temperature, pressure, level, displacement, etc. The transducer's output is equal to the input, but it has an electrical form. For instance, a temperature transducer converts the temperature into an equivalent electrical signal. The signal is employed to control the temperature and display it.

It is noteworthy to say that any device that can convert one form of energy into another is a transducer. Take, for example, a speaker. The speaker converts an electrical signal to pressure waves, so it is called a transducer. However, an electrical transducer just converts a quantity to an electrical form.

Each transducer consists of two essential parts: The sensing element and the traducing element.

The sensing or detector element is the part of the system which receives and sends the response to the physical sensation. The response of this element is dependent on physical phenomena.

Another critical part of the transducer is the traducing element. This part is called the secondary transducer in some references. The primary responsibility of the transduction element is converting the output of the sensing element into an electrical signal.

A transducer also has other elements such as power supply calibrating, signal processing, amplifier, etc.

It is quite demanding to measure the exact magnitude of the physical forces like temperature, pressure, etc. However, if it is converted to an electrical signal, the value can be measured simply. A transducer converts the physical quantities into an electrical signal which can easily be handled and transmitted for measurement. Here we have the advantages of this conversion:

• The weakening and boosting of electrical signals can be done simply.
• The electrical signal produces less friction error.
• Very compact and accurate components are used for measuring the electrical signal, so it guarantees the validity of monitoring.
• The power which is required for controlling the electrical systems is low enough.
• The electrical signals can be transmitted and processed for measurement without any trouble

Types of Transducer

Transducers can be classified in several ways. In what follows, you can see three ways of classification.

The first classification is based on the quantity converted. Pressure and temperature transducers, which convert pressure and temperature into electrical signals, are the most common examples.

The second classification of transducers regards the physical quantity, which will be converted to electrical quantity. An example of this type is the change in resistance of a copper element, which is its physical property, in proportion to the change in temperature.

We can also classify them based on the source of energy. In this way, the transducers are categorized into two types. Whether the source of energy is mandatory or not explains the type of them in this classification.

Types of transducer based on Measured Quantity

In this criterion, the transducers can be classified as:

• Temperature transducer (such as thermocouple), a device that converts the thermal quantity into the physical one.
• Displacement transducer (for example, LVDT) that transforms the linear motion into an electrical signal.
• Pressure transducer (such as diaphragm), which is an instrument that measures the pressure of a fluid, denoting the force the fluid is applying on contacted surfaces.
• Flow transducer, which is utilized to measure liquid and air flow velocity.
• Oscillator transducer that can be used to measure pressure, displacement, or force by converting it to a voltage.
• Inductive transducer, in which a movement among a conductor beside the magnetic field causes a voltage inside the conductor.

Types of Transducer based on Working Principles

If we want to classify these elements regarding their principle of operation, we will have:

• Photovoltaic (such as a solar cell), which converts the light energy into electrical energy. It is made of semiconductor material. The photoelectric transducer uses a photosensitive element, which ejects the electrons when the beam of light absorbs through it.

• Piezoelectric transducer, which is an electroacoustic transducer aid for conversion of pressure or mechanical stress into another electrical force. It is used to measure the physical quantity like , stress, force, pressure, etc., which is not possible to measure directly.

• Hall effect transducer, which is used for measuring the magnetic field by converting the field into an emf. The straight determination of the magnetic field is not achievable. Therefore, the Hall Effect Transducer is used. It converts the magnetic field into an electric quantity ,which is readily estimated by the analogue and digital measures.

• Photoconductors, which is used to convert the light energy into electrical energy. It is composed of semiconductor substance. The photoelectric transducer utilizes a photosensitive element, which discharges the electrons when the beam of light absorbs through it.

• Electromagnetic acoustic transducer (EMAT), which is a transducer used for generation of non-contact acoustic wave and reception in conducting substance. It does not demand direct coupling with the surface of the material.

  Types of Transducer based on the Presence or Absence of External Power Source

In this classification, we have two types of transducers, which are:

• Active Transducers
• Passive Transducers

If the transducer is not dependent on the external energy source and does not need any power source to operate, we have an active transducer. Their principle of working is energy conversion and produces an electrical signal proportional to the physical quantity input. To exemplify, we can put the thermocouple in the class of active transducer.

If the energy source is available and required for the transducer's operation, we have a passive one. These types produce an output signal in the form of some variation in capacitance, resistance, or any other electrical parameter. Then the produced signals will be converted to an equivalent voltage or current signal. In this group, we have a photocell. A photocell varies the resistance of the cell when light falls on it. This change in resistance is converted to a proportional signal with the help of a bridge circuit. In this way, it can be used to measure light intensity.