Ohmic (resistive) sensors. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Electrician

Sensors. Ohmic (resistive) sensors. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Electrician's Handbook

Ohmic (resistive) sensors - devices, the principle of operation of which is based on a change in their active resistance with a change in length l, cross-sectional area S or resistivity p.

The principle of operation is described, respectively, by the formula R=pl/S.

In addition, the dependence of the active resistance value on the contact pressure and illumination of the photocells is used. According to this Ohmic sensors are divided into groups:

contact;
potentiometric (rheostatic);
strain gauge;
thermistor;
photoresistive.

Contact sensors are the simplest type of resistor sensors that convert the movement of the primary element into an abrupt change in the resistance of the electrical circuit. With the help of contact sensors, they measure and control forces, displacements, temperature, sizes of objects, control their shape, etc.

Contact sensors are:

travel and limit switches;
contact thermometers;
electrode sensors used primarily to measure the limit levels of electrically conductive liquids.

Contact sensors can operate on both direct and alternating current. Depending on the measurement limits, contact sensors can be single-limit and multi-limit. The latter are used to measure values that vary within a significant range, while parts of the resistor R included in the electrical circuit are shorted in series.

Lack of contact sensors - the complexity of continuous monitoring and the limited service life of the contact system. But due to the extreme simplicity of these sensors, they are widely used in automation systems.

Rheostatic sensors are a variable resistance resistor. The input value of the sensor is the movement of the contact, and the output value is the change in its resistance. The moving contact is mechanically connected to the object whose displacement (angular or linear) is to be transformed.

The most widespread is the potentiometric circuit for switching on a rheostat sensor, in which the rheostat is switched on according to a voltage divider circuit. Recall that voltage divider called an electrical device for dividing direct or alternating voltage into parts.

The voltage divider allows you to remove (use) only part of the available voltage through the elements of an electrical circuit consisting of resistors, capacitors or inductors. A variable resistor connected according to a voltage divider circuit is called potentiometer.

Typically, rheostat sensors are used in mechanical measuring instruments to convert their readings into electrical quantities (current or voltage), for example, in float meters for liquid levels, various pressure gauges.

The sensor in the form of a simple rheostat is almost never used due to the significant non-linearity of its static characteristic.

I_н= f(x)Where I_н - load current.

The output value of such a sensor is the voltage drop UBbIX between the movable and one of the fixed contacts. Output voltage versus displacement х contact U_O = f(x) corresponds to the law of change of resistance along the potentiometer. The law of distribution of resistance along the length of the potentiometer, determined by its design, can be linear or non-linear.

Potentiometric sensors, which are structurally variable resistors, are made of various materials - winding wire, metal films, semiconductors, etc.

Strain gauges (strain gauges) are used to measure mechanical stresses, small deformations, vibration. The action of strain gauges is based on the tensoreffect, which consists in changing the active resistance of conductor and semiconductor materials under the influence of forces applied to them.

Thermometric sensors (thermistors) - resistance depends on temperature. Thermistors are used as sensors. two ways.

1 method. The temperature of the thermistor is determined by the environment; the current passing through the thermistor is so small that it does not heat up the thermistor. Under this condition, the thermistor is used as a temperature sensor and is often referred to as a "resistance thermometer".

2 method. The temperature of the thermistor is determined by the degree of heating by a constant current and the cooling conditions. In this case, the steady temperature is determined by the heat transfer conditions of the thermistor surface (the speed of the environment - gas or liquid - relative to the thermistor, its density, viscosity and temperature), so the thermistor can be used as a sensor for flow velocity, ambient thermal conductivity, gas density, etc. P.

In sensors of this kind, a kind of two-stage conversion takes place: the measured value is first converted into a change in the temperature of the thermistor, which is then converted into a change in resistance.

Thermistors are made from both pure metals and semiconductors. The material from which such sensors are made must have a high temperature coefficient of resistance, if possible a linear dependence of resistance on temperature, good reproducibility of properties and inertness to environmental influences. To the greatest extent, platinum satisfies all these properties; in a little less copper и nickel.

Compared to metal thermistors, semiconductor thermistors (thermistors) have a higher sensitivity.

Author: Koryakin-Chernyak S.L.

See other articles Section Electrician's Handbook.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

A New Way to Control and Manipulate Optical Signals 05.05.2024

The modern world of science and technology is developing rapidly, and every day new methods and technologies appear that open up new prospects for us in various fields. One such innovation is the development by German scientists of a new way to control optical signals, which could lead to significant progress in the field of photonics. Recent research has allowed German scientists to create a tunable waveplate inside a fused silica waveguide. This method, based on the use of a liquid crystal layer, allows one to effectively change the polarization of light passing through a waveguide. This technological breakthrough opens up new prospects for the development of compact and efficient photonic devices capable of processing large volumes of data. The electro-optical control of polarization provided by the new method could provide the basis for a new class of integrated photonic devices. This opens up great opportunities for ... >>

Primium Seneca keyboard 05.05.2024

Keyboards are an integral part of our daily computer work. However, one of the main problems that users face is noise, especially in the case of premium models. But with the new Seneca keyboard from Norbauer & Co, that may change. Seneca is not just a keyboard, it is the result of five years of development work to create the ideal device. Every aspect of this keyboard, from acoustic properties to mechanical characteristics, has been carefully considered and balanced. One of the key features of Seneca is its silent stabilizers, which solve the noise problem common to many keyboards. In addition, the keyboard supports various key widths, making it convenient for any user. Although Seneca is not yet available for purchase, it is scheduled for release in late summer. Norbauer & Co's Seneca represents new standards in keyboard design. Her ... >>

The world's tallest astronomical observatory opened 04.05.2024

Exploring space and its mysteries is a task that attracts the attention of astronomers from all over the world. In the fresh air of the high mountains, far from city light pollution, the stars and planets reveal their secrets with greater clarity. A new page is opening in the history of astronomy with the opening of the world's highest astronomical observatory - the Atacama Observatory of the University of Tokyo. The Atacama Observatory, located at an altitude of 5640 meters above sea level, opens up new opportunities for astronomers in the study of space. This site has become the highest location for a ground-based telescope, providing researchers with a unique tool for studying infrared waves in the Universe. Although the high altitude location provides clearer skies and less interference from the atmosphere, building an observatory on a high mountain poses enormous difficulties and challenges. However, despite the difficulties, the new observatory opens up broad research prospects for astronomers. ... >>

Random news from the Archive

Nvidia chatbot that works without internet 16.02.2024

Nvidia introduced its own chatbot called Chat with RTX, which can work without Internet access. This cutting-edge service is already available as a demo for Windows 11 users and can function offline.

Chat with RTX from Nvidia represents a new era in local chatbots, promising a seamless and secure experience directly on your computer.

Chat with RTX lets you run a local AI chatbot right on your computer. Users can feed it files, documents, and videos to create summaries, analyze information, and generate relevant answers based on the data provided.

The program runs on a PC and requires an RTX 30 or 40 series video card with a minimum of 8 GB of video memory and 16 GB of RAM. It operates locally, and Nvidia assures that this eliminates the possibility of leaking personal data, since there is no access to cloud servers.

Chat with RTX successfully copes with data analysis tasks and can become a useful tool for journalists and anyone who works with large amounts of information.

The app can process YouTube videos as well as parse PDFs to extract key information, acting almost instantly without the latency associated with cloud-based chatbots such as ChatGPT or Copilot.

Chat with RTX is currently in early developer release and has some limitations. Nvidia is not positioning it as a completely complete solution, but rather as a promising start in the development of a new ChatGPT analogue.

The Chat with RTX installation file is approximately 35GB in size and can be downloaded from Nvidia's official website.

Other interesting news:

▪ Probiotic capable of destroying antibiotic-resistant bacteria

▪ Potatoes with "awakened" genes successfully resist late blight

▪ TV advertisement magazine

▪ LEDs emit ultraviolet light

▪ Passive cooling of the car interior

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site for the Musician. Selection of articles

▪ article by Gargantua. Popular expression

▪ article Why do Mexicans call Americans gringos? Detailed answer

▪ article Technician-Designer. Job description

▪ article Golden-red mordant for brass items. Simple recipes and tips

▪ article Voltage converter for Ts20 avometer. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews