We make free electricity - a simple homemade generator. About thermocouples: what they are, principle of operation, connection, application

People have always strived to save money, and in an era of ever-increasing utility bills, this is not at all surprising. Today there are already ways in which a person can obtain free electricity that is free for him. As a rule, these are certain do-it-yourself installations, which are based on an electric generator.

Thermoelectric generator and its structure

A thermoelectric generator is a device that allows you to generate electrical energy from heat. This is an excellent steam source of electricity, although with low efficiency.

Essentially, thermoelectricity is the direct conversion of heat into electricity in liquid or solid conductors, and then the reverse process of heating and cooling the contact various conductors by using electric current.

Heat generator device:

• The thermal generator has two semiconductors, each consisting of a certain number of electrons;
• They are also interconnected by a conductor, above which there is a layer capable of conducting heat;
• A thermionic conductor is also attached to it for transmitting contacts;
• Next comes the cooling layer, followed by the semiconductor, whose contacts lead to the conductor.

Unfortunately, a heat and power generator is not always able to operate with high power, so it is used mainly in everyday life, and not in production.

Today, the thermoelectric converter is almost never used anywhere. It “requests” a lot of resources, it also takes up space, but the voltage and current that it can generate and convert are very small, which is extremely unprofitable.

Solar thermal generator of electricity and radio waves

Sources electrical energy can be very different. Today, the production of solar thermoelectric generators has become increasingly popular. Such installations can be used in lighthouses, in space, in cars, and in other areas of life.

RTG (which stands for radionuclide thermoelectric generator) works by converting the energy of isotopes into electrical energy. This is very economical way, allowing you to get practically free electricity and the possibility of lighting in conditions of lack of electricity.

Features of RTG:

• It is easier to obtain a source of energy from the decays of isotopes than, for example, doing the same thing by heating a burner or kerosene lamp;
• The generation of electricity and the decay of particles is possible with the presence of special isotopes, because the process of their decay can last for decades.

When using such an installation, you need to understand that when working with old models of equipment, there is a risk of receiving a dose of radiation, and it is very difficult to dispose of such a device. If destroyed incorrectly, it can act as a radiation bomb.

When choosing an installation manufacturer, it is better to choose companies that have already proven themselves. Such as Global, Altec, Tgm, Kryotherm, Termiona.

By the way, another good way to get electricity for free is a generator that collects radio waves. It consists of pairs of film and electrolytic capacitors, as well as low-power diodes. An insulated cable of about 10-20 meters is used as an antenna and another grounding wire is attached to a water or gas pipe.

How to make a Peltier element with your own hands

A typical Peltier element is a plate assembled from parts various metal, with connectors for connecting to the network. Such a plate passes current through itself, heating up on one side (for example, up to 380 degrees) and working from the cold on the other.

This thermogenerator has the opposite principle:

• One side can be heated by burning fuel (for example, a wood fire or some other raw material);
• The other side, on the contrary, is cooled by a liquid or air heat exchanger;
• Thus, current is generated on the wires, which can be used according to your needs.

True, the device’s performance is not very high, and the effect is not impressive, but, nevertheless, such a simple homemade module can easily charge a phone or connect an LED flashlight.

This generator element has its advantages:

• Silent operation;
• The ability to use what is at hand;
• Light weight and mobile.

Such homemade stoves have begun to gain popularity among those who like to spend the night in the forest by the fire, taking advantage of the gifts of the earth and who are not averse to getting electricity for free.

The Peltier module is also used to cool computer boards: the element is connected to the board and as soon as the temperature becomes higher than permissible, it begins to cool the circuits. On one side, cold air space enters the device, and on the other, hot air. The 50X50X4mm (270w) model is popular. You can buy such a device in a store or make it yourself.

By the way, connecting a stabilizer to such an element will allow you to get an excellent output charger For household appliances, and not just a thermal module.

To make a Peltier element at home, you need to take:

• Bimetal conductors (about 12 pieces or more);
• Two ceramic plates;
• Cables;
• Soldering iron.

The manufacturing scheme is as follows: the conductors are soldered and placed between the plates, after which they are tightly fixed. In this case, you need to remember about the wires, which will then be attached to the current converter.

The scope of use of such an element is very diverse. Since one of its sides tends to cool, using this device you can make a small camping refrigerator, or, for example, a car air conditioner.

But, like any device, this thermocouple has its pros and cons. The advantages include:

• Compact size;
• Possibility of working with cooling or heating elements together or each separately;
• Quiet, almost silent operation.

Cons:

• The need to control temperature differences;
• High energy consumption;
• Low level of efficiency at high cost.

Simple homemade generator

Despite the fact that these devices are not popular now, at the moment there is nothing more practical than a thermogenerating unit, which, when traveling, is quite capable of replacing an electric stove, a light bulb, or helping out if the battery charger breaks down. mobile phone, power the electric window. Such electricity will also help at home in case of a power outage. You can get it for free, one might say, on a ball.

So, to make a thermoelectric generator, you need to prepare:

• Voltage stabilizer;
• Soldering iron;
• Any body;
• Radiators for cooling;
• Thermal paste;
• Peltier heating elements.

Device assembly:

• First, the body of the device is made, which should be without a bottom, with holes at the bottom for air and at the top with a stand for the container (although this is not necessary, since the generator may not work on water);
• Next, a Peltier element is attached to the case, and a cooling radiator is attached to its cold side through thermal paste;
• Then you need to solder the stabilizer and the Peltier module, according to their poles;
• The stabilizer should be very well insulated to prevent moisture from getting in;
• It remains to check its operation.

By the way, if it is not possible to get a radiator, you can use it instead computer cooler or car generator. Nothing bad will happen from such a replacement.

The stabilizer can be purchased with a diode indicator that will give a light signal when the voltage reaches the specified value.

Such a heat generator warms up in about 30 seconds, but the voltage it consumes already reaches several volts. After a few minutes of warming up, the generator will be ready for use.

Do-it-yourself thermocouple: process features

What is a thermocouple? A thermocouple is an electrical circuit consisting of two different elements with electrical contact.

The thermoEMF of a thermocouple with a temperature difference of 100 degrees at its edges is approximately 1 mV. To make it higher, several thermocouples can be connected in series. The result is a thermopile, the thermoEMF of which will be equal to the total sum of the EMF of the thermocouples included in it.

The thermocouple manufacturing process is as follows:

• A strong connection is created between the two different materials;
• Take a voltage source (for example, car battery) and wires of different materials pre-twisted into a bundle are connected to one end;
• At this time, you need to bring a lead connected to graphite to the other end (a regular pencil lead will do here).

By the way, for safety reasons it is very important not to work under high voltage! The maximum indicator in this regard is 40-50 Volts. But it is better to start with small powers from 3 to 5 kW, gradually increasing them.

There is also a “water” way to create a thermocouple. It consists in ensuring the heating of the connected wires of the future structure by an arc discharge that appears between them and a strong solution of water and salt. During this interaction, “water” vapors bind the materials together, after which the thermocouple can be considered ready. In this case, it matters what diameter the product harness is. It shouldn't be too big.

Free electricity with your own hands (video)

Getting free electricity is not as difficult as it seems. Thanks to various kinds generators operating with different sources, it’s no longer scary to be left without light during a power outage. A little skill and you already have your own mini-station for generating electricity.

Now we will understand the purpose of a thermocouple in a gas boiler, its features and operating principles. In the end, we’ll figure out how to carry out repairs yourself.

Find out the price and buy heating equipment and related products you can find here. Write, call and come to one of the stores in your city. Delivery throughout the Russian Federation and CIS countries.

Any boiler, regardless of the type and principle of its operation, needs a thermocouple - a device that will control the temperature in the combustion chamber and automatically shut off the gas supply when the flame disappears.

For gas boiler — necessary element in the heating system, which helps to avoid overheating of the boiler and the possibility of its breakdown.

Thermocouple for gas boiler

To understand how a thermocouple works in a gas boiler, you first need to get acquainted with its structure and principle of operation.

A thermocouple is a structure of two conductor plates, which consists of different alloys. The device is quite simple, but at the same time reliable.

Operating principle of this device based on physical phenomenon- Seebeck effect.

The process of formation of electromotive force at the interface of two dissimilar conductors, the contacts of which have temperature differences. Seebeck effect

If two parts made of dissimilar metals are firmly connected and the junction is heated, then a potential difference—voltage—will appear at the cold ends of the soldered conductor. When voltage appears, the valve immediately opens automatically, allowing fuel to pass to.

The operating principle of a gas boiler thermocouple

Types of thermocouples

Today, the boiler equipment market is distinguished by an abundance of various thermocouples, which are divided into several types. The metal used in their manufacture is the main criterion on the basis of which they are differentiated.

Made from base metals

Made from precious metals

In boiler automation systems, thermocouples of the following types are most often used: E, J, K.

Connection and testing

The thermocouple must be connected using electrodes (wires) made of the same material as the thermocouple being connected.

Or metal wires can be used, which have characteristics similar to those of the electrodes on the thermocouple itself.

Before connecting thermocouples for heating boilers, it is important to strip the ends of the wires to remove oxides that affect the accuracy of the measurements. And during installation, it is important to ensure that the fuel outlet and supply pipes are lowered straight down.

If the thermocouple is broken, as a rule, it is no longer possible to restore it, so it is important to know how to check the thermocouple with a multimeter on a gas boiler.

The working thermocouple should operate after 10-30 seconds of heating

To check its functionality, just connect one end to a multimeter - a measuring sensor, and heat the other end using either a lighter.

A combined electrical measuring instrument, which can be digital and analog, combines several functions (at least the functions of a voltmeter, ohmmeter, ammeter). Multimeter

The working thermocouple should have a voltage around 50 mV.

If the thermocouple is confirmed to be faulty, you can replace it yourself.

DIY thermocouple repair

To fix the problem yourself you need to:

• unscrew the clamping nut wrench and and get its end;
• Use a zero-string lacing to remove dirt;
• check the thermocouple with a multimeter;
• make sure that all indicators comply with the standards;
• put the thermocouple back together and start the boiler.

If you cannot repair the thermocouple, you can always buy a new one. Russian market offers a wide range of these devices produced by various manufacturers, for example, ABAT, AOGV, AKGV. Their price ranges from 300 to 2000 rubles. On gas boilers foreign production (for example, Bosch, Viessmann, Vaillant) the price of a thermocouple will be higher.

Today thermocouples were found active use c, there is a wide choice on the market, and everyone has the opportunity to purchase a universal thermocouple. However, when choosing a thermocouple yourself, you may encounter a number of difficulties. You should contact a specialist who will tell you how to choose a device that meets all the characteristics of a gas boiler. You can also use the dependency table technical characteristics device with the characteristics of a gas boiler.

In process automation, it is very often necessary to take indicators of temperature changes in order to load them into control systems for the purpose of further processing. This requires high-precision, low-inertia sensors that can withstand high temperature loads within a certain measurement range. Thermocouples are widely used as thermoelectric converters - differential devices that convert thermal energy to electric.

The devices are also a simple and convenient temperature sensor for a thermoelectric thermometer designed to make accurate measurements over fairly wide temperature ranges. In particular, control automation of gas boilers and other heating systems triggered by an electrical signal coming from a thermocouple-based sensor. The sensor designs provide the necessary measurement accuracy in the selected temperature range.

Device and principle of operation

The thermocouple is structurally composed of two wires, each of which is made of different alloys. The ends of these conductors form a contact (hot junction) made by twisting, using a narrow weld or butt welding. The free ends of the thermocouple are closed using compensation wires to the contacts of the measuring device or connected to automatic device management. At the connection points another so-called cold junction is formed. The device is shown schematically in Figure 1.

Rice. 1. Scheme of the thermocouple structure

The hot junction area is highlighted in red, the cold junction is highlighted in blue.

The electrodes consist of different metals(metal A and metal B), which are colored in different colors. In order to protect thermoelectrodes from aggressive hot environments, they are placed in a sealed capsule filled with an inert gas or liquid. Sometimes ceramic beads are placed on the electrodes, as shown in Fig. 2).

The operating principle is based on the thermoelectric effect. When a circuit is closed, for example with a millivoltmeter (see Fig. 3), a thermo-emf occurs at the junction points. But if the electrode contacts are at the same temperature, then these EMFs compensate each other and no current occurs. However, if you heat the hot solder joint with a torch, then, according to the Seebeck effect, a potential difference will arise, supporting the existence of an electric current in the circuit.

It is noteworthy that the voltage at the cold ends of the electrodes depends proportionally on the temperature in the hot junction area. In other words, in a certain temperature range we observe a linear thermoelectric characteristic that displays the dependence of the voltage on the magnitude of the temperature difference between the hot and cold junction points. Strictly speaking, we can talk about linearity of indicators only in the case when the temperature in the cold junction region is constant. This should be taken into account when calibrating thermocouples. If the temperature changes at the cold ends of the electrodes, the measurement error can be quite significant.

In cases where it is necessary to achieve high accuracy of indicators, the cold junctions of the measuring transducers are placed even in special cameras, in which temperature environment maintained at the same level by special electronic devices using data (the diagram is shown in Fig. 4). With this approach, it is possible to achieve measurement accuracy with an error of up to ± 0.01 °C. True, such high accuracy is needed only in a few technological processes. In some cases, the requirements are not so stringent and the error can be an order of magnitude lower.

The error is affected not only by temperature changes in the environment surrounding the cold junction. The accuracy of the readings depends on the type of construction, wiring diagram, and some other parameters.

Types of thermocouples and their characteristics

Different alloys used to make thermocouples have different thermo-EMF coefficients. Depending on what metals the thermoelectrodes are made of, the following main types of thermocouples are distinguished:

• TPP13 – platinum-rhodium-platinum (type R);
• TPP10 – platinum-rhodium-platinum (type S);
• TPR – platinum-rhodium-platinum-rhodium (type B);
• TFA – iron-constantan (type J);
• TMKn – copper-constantan (type T);
• TNN – nichrosil-nisil (type N);
• THA – chromel-alumel (type K);
• THCn – chromel-constantan (type E);
• THC – chromel-copel (type L);
• TMK – copper-copel (type M);
• TSS – sil-silin (type I);
• TVR – tungsten rhenium (types A-1 – A-3).

Technical requirements for thermocouples are specified by parameters defined by GOST 6616-94, and their NSC (nominal static conversion characteristics), optimal measurement ranges, installed classes tolerances are regulated by IEC 62460 standards, and are defined by . Let us also note that the NSC in tungsten-rhenium thermocouples was absent from the IEC tables until 2008. To date, these standards do not define the characteristics of the Chromel-Kopel thermocouple, but their parameters are still regulated by GOST R 8.585-2001. Therefore, imported L-type thermocouples are not a complete analogue of the domestic THC product.

Thermal sensors can also be classified according to other criteria: by type of junction, number of sensitive elements.

Depending on the purpose of the temperature sensor, thermocouple junctions may have different configuration. There are single-element and two-element junctions. They can be either grounded to the body of the bulb or ungrounded. You can understand the diagrams of such structures from Figure 5.

The letters indicate:

• And – one junction, isolated from the body;
• H – one junction connected to the body;
• AI – two junctions isolated from each other and from the housing;
• 2I – double junction, isolated from the housing;
• IN – two junctions, one of which is grounded;
• LV – two non-insulated junctions connected to the housing.

Grounding to the housing reduces the inertia of the thermocouple, which, in turn, increases the speed of the sensor and increases the accuracy of real-time measurements.

In order to reduce inertia, some models of thermoelectric converters leave a hot junction outside the protective flask.

Multipoint thermocouples

Temperature measurements are often required various points simultaneously. Multipoint thermocouples solve this problem: they record temperature data along the axis of the transmitter. This need arises in the chemical and petrochemical industries, where it is necessary to obtain information about the temperature distribution in reactors, fractionation columns and other vessels intended for chemical processing of liquids.

Multipoint temperature measuring transducers increase efficiency, do not require complex maintenance. The number of data collection points can reach up to 60. In this case, only one flask and one entry point into the installation are used.

Thermocouple comparison table

Above we looked at the types of thermoelectric converters. The reader most likely has a reasonable question: Why are there so many types of thermocouples?

The fact is that the measurement accuracy declared by the manufacturer is only possible in a certain temperature range. It is in this range that the manufacturer guarantees the linear characteristics of its product. In other ranges, the dependence of voltage on temperature may be nonlinear, and this will certainly affect the accuracy. It should be taken into account that materials have different degrees of fusibility, so there is a limiting operating temperature for them.

To compare thermocouples, tables have been compiled that display the main parameters of measuring transducers. As an example, we present one of the table options for comparing common thermocouples.

Table 1.

Connection methods

Each new connection point between dissimilar metal wires creates a cold junction, which can affect the accuracy of the readings. Therefore, thermocouple connections are made, if possible, with wires made of the same material as the electrodes. Manufacturers usually supply products with compensation wires connected.

Some measuring instruments contain reading correction circuits based on a built-in thermistor. Wires are simply connected to such devices, observing their polarity (see Fig. 6).

The “break” connection scheme is often used. The measuring device is connected through a conductor of the same type as the terminals (most often copper). Thus, there is no cold junction at the connection points. It is formed in only one place: at the point of connection of the wire to the thermocouple electrode. Figure 7 shows a diagram of such a connection.

When connecting a thermocouple, the measuring systems should be placed as close as possible to avoid using too long wires. In any wire, interference is possible, which increases with increasing length of the wire. If you can get rid of radio interference by shielding the wiring, then dealing with pickup currents is much more difficult.

Some circuits use a compensating thermistor between the meter terminal and the cold junction. Since the external temperature equally affects the resistor and the free junction, this element will correct such effects.

And finally: by connecting the thermocouple to measuring device, it is necessary to carry out the calibration procedure using calibration tables.

Application

Thermocouples are used wherever temperature measurement in a process environment is required. They are used in automated systems management as . Thermocouple type TVR, which has an impressive thermoelectrode diameter, is indispensable where it is necessary to obtain data on very high temperatures, in particular in metallurgy.

Gas boilers, convectors, water heaters are also equipped with thermoelectric converters.

Advantages

• high measurement accuracy;
• fairly wide temperature range;
• high reliability;
• ease of maintenance;
• cheapness.

Flaws

The disadvantages of the products are the following factors:

• the influence of free junctions on instrument performance;
• limitation of the operating range by the nonlinear dependence of the thermal force on the degree of heating, which creates difficulties in the development of secondary signal converters;
• at long-term operation under conditions of temperature changes, calibration characteristics deteriorate;
• the need for individual calibration to obtain high measurement accuracy, within an error of 0.01 ºC.

Due to the fact that problems associated with shortcomings can be solved, the use of thermocouples is more than justified.

Video on the topic

Most heating and measuring items that we use in everyday life require the use of special control elements. Such controllers (thermocouples) protect devices from overheating and damage. The thermocouple can be used for both small home measurements and laboratory experiments. To do this, you don’t need to specifically look for it in stores. You can understand its structure and make a thermocouple for a multimeter with your own hands.

Description and characteristics

A thermocouple is a device, consisting of two different conductors that are connected at one or more points by compensation wires. When a temperature measurement occurs at one end of the wire, a voltage of a certain value and strength is created at the other. This device is used to control temperature and also to convert temperature into electrical current.

The temperature sensor is quite inexpensive. This device is quite standard and measures a wide range of temperatures. The only drawback in the operation of the element is the inaccuracy, which can be up to 1 °C, and this is quite a lot for such values.

Making a thermocouple at home is not difficult. You just need to remember that these devices are created from special alloys, so there is a predictable and consistent relationship between voltage and temperature.

There are sensors different types. They are classified according to the type of alloy metal used:

1. chromel - alumel;
2. platinumrhodium - platinum.

The environment of use also depends on the composition, because such controllers are used both in science and industry, and at home - for boilers, columns, ovens.

Operating principle

Thermocouple is the most popular thermal sensor k, which was discovered in 1822 by the German physicist Thomas Seebeck. That is why the principle of operation of such an element is often called the Seebeck effect.

In books and textbooks, this effect is described as follows: if the junctions of conductors have non-identical temperatures, then an electric force (thermopower) is formed between them, the value of which is proportional to the temperature difference between the junctions.

Here it must be emphasized that it is the temperature difference that is worth taking into account, and not any indicator at all. In addition, if both junctions have the same temperature, then thermopower will not occur in the circuit.

Before you start making a temperature sensor, you need to prepare all the materials and tools. Thermocouple electrodes consist of dissimilar materials, to select which you need to decide on the type of product and scope of use.

Types of temperature sensors are designated by letters Latin alphabet and have their own characteristics. For example, the popular TYPE K model consists of a chromel-alumel alloy, and its measurement range is 200−1200 °C. Having made simple calculations, we can talk about nonlinearity (thermopower -35 - 32 μV/°C), while the nonlinearity of the characteristic should be the smallest. In this case, the measurement error will be very small.

The thermocouple can be located at a remote distance from the equipment itself. To do this, it is connected using a special cable. The cable itself is made from the same materials as the thermocouple. The only difference is the diameter.

Making a temperature sensor

To make a thermocouple with your own hands, you need to purchase wire from suitable materials. The diameter is important here, since the error in temperature measurement depends on it. It is recommended to use wire of a smaller diameter, especially if small objects will be examined.

The material depends on the temperature range with which it is intended to work. The most common options: chromel-alumel, copper-constantan. The manufacture itself consists of creating a connection, an alloy of two wires. Often, some kind of voltage source is used for this (for example, a car battery or transformer).

The further stages of work are as follows:

1. the free ends of the twisted wire are connected to one of the poles of the voltage source;
2. the output is connected to the other pole, which is additionally connected to a graphite pencil.

Whenever electric arc a connection occurs between the thermocouple wires. In this case, the voltage for connecting the wires is selected through experiment. As a rule, optimal value 40−50 V, but it may be less, as it depends on the materials and length of the product.

Another main point- compliance with safety regulations. It is very important not to use too high a voltage or touch exposed wires. It's better to isolate them special tape or cover with a ceramic tube.

This is the simplest and affordable way making a thermocouple for a multimeter with your own hands. Sometimes thermocouple wires are soldered using a soldering iron. But then you will have to additionally purchase special solder and adhere to certain operating temperatures.

Meanwhile, there are many other examples of equipment, the normal functioning of which becomes impossible without a failed temperature sensor, which looks like an ordinary wire. At the same time, the issue of making a thermocouple with your own hands is often on the agenda not so much as one of the ways to save money, but rather as the impossibility of selecting a replacement (for example, an outdated model, the production and supply of spare parts for which has long been discontinued service center). In fact, a burnt-out temperature sensor is not at all a reason to throw broken equipment into a landfill, because there are many simple and easy ways to do it manually, and craftsmen offer two main options for conducting work - through the use of a gas welding installation of any type or by making a connection various materials without her.

So, the easiest way to make a high-quality replacement for a failed temperature sensor with your own hands is to weld a joint of three materials such as copel, alumel and chromel. In this case, they must first be twisted into a tight bundle and only then welded into a single connection. The only difficulty that may arise on the way to your goal is that it is not always possible to find or purchase necessary materials. Often you have to look for them in fully automated boiler rooms, metal collection points, or in markets where various parts, wires and fasteners are sold. As for the gas welding machine, you should not worry too much and give up on your plan if it is not available or the person does not have experience working with installations of this kind, because there is a worthy alternative for it.

So, main task When carrying out high-quality welding without the use of a gas welding machine, it is necessary to provide a powerful voltage source, which can be used as either a laboratory-type autotransformer, or, at worst, a car battery. The procedure is also not at all complicated and usually consists of pre-twisted wires made of different materials into a tight bundle and connecting the free ends of one side to the pole of the voltage source, while the output is connected to the other free ends of the future thermocouple. firmly connected to a piece of graphite. As the last material, you can use a regular pencil rod, which can be easily removed by carefully sawing wooden blank in the direction of the longitudinal section.

Strong welding of mechanically connected wires is ensured by creating an electric arc when attaching a graphite fragment, while great importance has full safety precautions, for which ideally small area completely protect the wires with insulating tape or special removable corrugation. However, to fully ensure your own safety and such measures, it is not enough and it is extremely important not to carry out work under high voltage, therefore, as much as possible acceptable standards In this regard, indicators are considered not exceeding 40-50 Volts. Ideally, it is better to start with low powers (their range can vary from three to five Volts), gradually increasing this indicator if this is necessary to ensure truly strong welding of elements twisted into a bundle.

There is another method for making a strong connection that does not involve the use of a gas welding machine. It consists in ensuring the heating of the mechanically connected wires of the future thermocouple due to the arc discharge arising between them and a strong solution from an ordinary table salt and distilled water. So, as a result of this effect on the wires, they melt and “glue” together, after which the thermocouple can be considered completely ready. In this case, the diameter of the bundle of the completed product is of great importance, which should not be too large. All valid values, as well as detailed diagrams on how to create an electric arc at home (the arrangement of wires relative to a water-salt solution or connecting them to a graphite rod) can be found without much difficulty on almost any network resource.