What is an Active Transducer? All You Should Know

As you know, a transducer’s primary function is to convert a physical quantity into an equivalent electrical signal. In typical electrical systems, the input is often an electrical signal; however, a non-electrical signal can be transformed into its equivalent electrical signal using electrical techniques.

An active transducer is a type of transducer that does not require an external power supply to generate output. It can convert physical impulses into electric signals independently. Active Transducers are crucial in measurement tools and are available from numerous suppliers, companies, manufacturers, and distributors. Linquip offers a wide selection of Active Transducers for sale.

Linquip’s website provides a comprehensive list of Active Transducer services that cover all manufacturer operations. Linquip vendors are available to assist you. Contact the Active Transducer Experts at Linquip to learn more about connecting with a diverse group of service providers who consistently deliver high-quality products.

Essentially, a transducer’s block diagram consists of two components: the sensing element and the transduction element. Transducers can be classified in various ways, one of which distinguishes between active transducers and passive transducers.

What is an Active Transducer?

An active transducer is a device that converts non-electrical quantities, such as temperature, pressure, and light, into electrical signals. Consequently, there are various types of active transducers based on the non-electrical quantity being measured.

This type of transducer does not require an external power source. It has a simple design and low resolution. Examples of active transducers include PV cells, thermocouples, and tachogenerators.

An active transducer is self-generating, meaning it can produce an electrical voltage or current output without using any external power source. These transducers derive the energy required for their operation from the measuring system. However, the output generated by active transducers is usually very small, necessitating additional amplification.

Types of Active Transducer

There are three types of active transducers:

Piezo Electric Transducer

Photo Electric Transducer

Thermo Electric Transducer

Below, we will discuss these three types of active transducers in detail.

Piezo Electric Transducer

A piezo electric transducer is a type of active transducer whose primary function is to generate an electrical quantity equivalent to the input pressure. Three substances that produce a piezoelectric effect are Quartz, Rochelle salts, and Tourmaline. These substances demonstrate the piezoelectric effect.

A piezoelectric transducer operates based on the piezoelectric effect, measuring variations in acceleration, strain, pressure, force, or temperature by converting this energy into an electrical one.

The electrical voltage generated by a piezoelectric transducer can be easily measured using voltage measuring tools. Since this voltage is a function of the force or pressure applied, the voltage reading allows us to infer the force/pressure. Thus, physical quantities such as mechanical stress and force can be directly measured using a piezoelectric transducer.

A piezoelectric transducer consists of a quartz crystal made of silicon and oxygen arranged in a crystalline structure (SiO2). Typically, the primary repeating unit, or unit cell, of a crystal is symmetrical; however, this is not the case for a piezoelectric quartz crystal. Despite the lack of symmetry, piezoelectric crystals remain electrically neutral.

The atoms may not be symmetrically arranged, but their electrical charges are balanced, meaning positive charges cancel out negative charges. Quartz crystals have the unique property of generating electrical polarity when mechanical stress is applied along a specific plane. There are fundamentally two types of stress: tensile stress and compressive stress.

In an unstressed quartz crystal, no charges are generated. Under compressive stress, positive charges are induced on one side, and negative charges are generated on the opposite side, causing the crystal to become longer and thinner. Under tensile stress, the charges are induced in the reverse manner compared to compressive stress, resulting in the quartz crystal becoming shorter and fatter.

Thermistors Applications

Thermistors have various applications, commonly used as thermistor thermometers to measure temperature in different liquid and air environments. Some popular applications include:

  • Used in Wheatstone bridge circuits
  • Employed as digital thermometers (thermostats)
  • Used for automotive purposes (e.g., measuring coolant and oil temperatures in trucks and cars)
  • Integrated into household instruments (such as microwaves, ovens, and fridges)
  • Used for circuit protection (e.g., surge protection)
  • Included in rechargeable batteries (to ensure the correct battery temperature is maintained)
  • Used for measuring the thermal conductivity of electrical materials
  • Employed in many fundamental electronic circuits
  • Thermistor: Principle of Working

The main working principle of a thermistor is that its resistance depends on its temperature. The resistance of a thermistor can be measured using an ohmmeter. If the exact relationship between temperature changes and the thermistor’s resistance is known, the temperature can be derived by measuring the thermistor’s resistance.

The type of material used in the thermistor determines the amount of temperature change. The relationship between a thermistor’s temperature and resistance is non-linear.

Thermistors are classified into two categories:

Negative Temperature Coefficient (NTC) Thermistor

Positive Temperature Coefficient (PTC) Thermistor

Thermocouple Transducer

Another kind of active transducer is the thermocouple. This transducer produces an output voltage corresponding to a change in temperature at the input. When different metal wires are connected to form two junctions, the arrangement is known as a thermocouple.

A thermocouple operates based on the thermoelectric effect, where a temperature difference is directly converted into an electric voltage. It is an electrical device for measuring temperature.

A thermocouple can measure a broad range of temperatures and is a simple, robust, and economical temperature sensor used in various industrial, home, office, and commercial applications.

Different configurations of thermocouples are available based on their applications, including thermocouple probes, probes with connectors, base wire thermocouples, infrared thermocouples, and just thermocouple wire.

Thermocouple: Principle of Working

A thermocouple consists of two plates of different metals connected at one end to form a junction.

The junction is placed on the element or surface where the temperature is to be measured, called the hot junction. The other end of the plates is kept at a lower temperature (room temperature), called the reference or cold junction.

The temperature difference between the two metals induces potential variations between the two points of the thermocouple plates, according to the Seebeck effect.

If the circuit is closed, a small amount of current flows through the circuit. The voltage measured by the voltmeter connected to the circuit is a function of the temperature variation between the two junctions. Therefore, by measuring the voltage, the temperature of the hot junction can be determined.

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