You will need

- multimeter, test leads with probes (supplied with the multimeter).

Instruction

1

Insert the test lead black to the COM terminal of the multimeter, then plug the test lead red to the VΩmA socket. Turning the switch of the measuring range, turn the unit on. For measurements of small resistance, turn the switch in the Ω sector and put in position opposite the numeral 200 (measurement Range 0.1 – 200 Ohms). Short between the probes (to check the measuring circuit on the circuit), the display should show the numeric value in the range 0.3 – 0.7. This resistance measuring wire. Each time the multimeter check the resistance value of the measuring wires. When it increases to 0.8 Ohms, replace the test leads. With open-loop wires, the display should show the digit 1 in the leftmost register (very high resistance infinity).

2

To measure touch both contacts in the test circuit. If the chain or the consumer current is OK, the multimeter readings will change: it will show some resistance. In the case of a test for an open in the power cord, fuse or "continuity" of the wires, the resistance should be very low (in the range of 0.7 – 1.5 Ohm). But when checking the electrical consumers (lights, heating elements, winding network transformers) may rise to 150 – 200 Ohms. Moreover, this dependence can be traced – the more powerful the consumer is current, the less resistance.

3

If multimeter readings do not change, switch the measuring range of resistance, put the switch in front of 2000 numbers (0 – 2000 Ohms). And then if the display does not change, switch to the next range and measure again. Note: when the lock opposite numbers 2000K sensitivity of a multimeter is very high and if at the same time take his left and right hands for the contact probe, the instrument will show the resistance of the body that will distort the readings on the multimeter.

Note

All check the circuit and the loads must be disconnected!

Useful advice

Before each measurement, check the measuring circuit for a short. Do not forget to check the battery status: when the device and put the battery the display will show the battery symbol.

# Advice 2 : How to measure resistance with a tester

There are three types of devices which can measure the resistance: a digital, dial, and bridges. Methods of using these gauges differ. An experienced handyman should be able to measure

**resistance**, using any of them.You will need

- digital multimeter, analog tester, ohmmeter or bridge resistance meter.

Instruction

1

Regardless of the devices you are going to use a resistor,

**the resistance**of which is measured, should be desoldering from the circuit. First it should be unplugged from power source and discharge any capacitors in it.2

To measure

**resistance**with a DMM, select switch mode resistance measurements and the coarse mode. Wire turn in a socket device corresponding to the measurement mode of resistance, and then connect to the probe resistor. If measured**resistance**is not a resistor, and the element whose conductivity depends on the direction of current, note that the DMM red probe there is a positive voltage.Sequential shift switch in the direction of more precise limits to achieve the disappearance of the overload. Read indicator, and the position of the switch find out what units they are expressed.3

Resistance measurement switches

- zero the scale resistance is at its end;

- after every shift limit the probe device must be closed, put an arrow special controller to zero, and only then carry out the measurement;

- some switch testers range is carried out not by turning the handle, and a permutation of the plug;

also some gauges require, in addition to range, enable measurement of resistance by a separate switch.

**the tester**is the same, but with a number of its features, namely:- switch the tester in the ohms positive terminal in most cases is on the black test probe;- zero the scale resistance is at its end;

- after every shift limit the probe device must be closed, put an arrow special controller to zero, and only then carry out the measurement;

- some switch testers range is carried out not by turning the handle, and a permutation of the plug;

also some gauges require, in addition to range, enable measurement of resistance by a separate switch.

4

Bridge meter use. Connecting it to the resistor, move the switch limits in one of these extremes. Rotate the knob from one end of the scale to another. If the indicator of the balance bridge (lighting, sound or pointer) never worked, choose a different limit. It again scroll the slider from one end to the other. This operation is repeated until then, until the bridge do not balance. Now, on a scale on the controller to determine

**the resistance**, and the switch position of limits - in what units it is expressed.# Advice 3 : How to measure the resistance of the resistor

The resistor is one of the main elements of any electrical circuit. Its main purpose is to create a certain resistance. Resistance can be measured with special devices or to identify a special marking on the body of the resistor.

You will need

- tester;
- calculator;
- table of markings.

Instruction

1

Take a tester who can work in ohmmeter mode. Connect it to the contacts

**of the resistor**and perform measurement. Since the resistance of the resistors is very different, adjust the sensitivity of the instrument. If the tester can only measure current and resistance, take the current source and assemble electric circuit including a resistor. When connecting the chain, be sure to monitor the current which passes through it, so as not to cause a short circuit. After the change of current in amperes, switch the tester to measure voltage. Connect it in parallel with the resistor and take readings in volts. Then find the resistance**of the resistor**by dividing the voltage value U and the current I (R=U/I). If you are using a constant current source, connecting devices2

If the resistor marked to find its resistance, without resorting to additional operations. Resistors are marked or digits or combination of numbers with letters, or a set of color bars.

3

If the resistor is indicated with three digits, the first two numbers identify tens and ones number, and the third digit is the degree 10 to which it should be raised to obtain the correct values. For example, if the resistor numbered 482, it means that its resistance is equal to 48∙102=4800 Ohms.

4

When the resistor marking SMD, the first two figures are taken as the coefficient, and the letter corresponds to the degree 10 to which it needs to multiply. All the values of the coefficients and the letters get in the table of marking of the SMD resistors EIA. The resistor may be the fourth letter of its accuracy. For example, if a resistor is marked 21ВF, its resistance will be equal to 162∙10=1620 Ohms ±1%.

5

If the drawn resistor color bands, use the table to determine the resistance

**of the resistor**by the colored marking. The first three labels correspond to the numbers that make up a coefficient, and the fourth – power of 10 by which to multiply the resulting factor.# Advice 4 : What is measured by the resistance

If included in the electrical circuit of a single current source to different conductors and the ammeter can be observed that the readings of the ammeter when different conductors are different. This is due to the electric resistance of the portion, from which, like voltage, depends on current.

## Resistance as a physical quantity

The electrical resistance of a conductor is a physical quantity, denoted by the letter R. the unit of resistance adopted 1 Ohm – the resistance of the conductor in which the current strength is 1 ampere at a voltage of 1 volt at the ends. Briefly write down this formula:

1 Ohm=1V/1A.

The units of resistance can be and multiple. So 1 milliohm (mω) – is a 0.001 Ohm, 1 kilo Ohm (kω) 1000 Ohms, 1 Megohm (MW) Is 1,000,000 Ohms.

## What is the cause of electrical resistance in conductors

If orderly moving in a conductor the electrons have not experienced any obstacles in their path, they could move by inertia indefinitely. But in reality this does not happen, because the electrons interact with the ions arranged in the crystal lattice of the metal. Their movement from this slows down and in 1 second through a cross section of the conductor is smaller number of charged particles. Therefore, the charge carried by the electrons in 1 second decreases, i.e., decreases the current strength. Thus, every conductor as though resists moving in this current, opposing him.

The reason for the resistance – collision of moving electrons with the ions of the crystal lattice.

## What is expressed in Ohm's law for subcircuit

In any electrical circuit, a physicist has to deal with three physical quantities – current, voltage and resistance. These values do not exist separately in themselves, but are linked by a certain ratio. Experiments show that the strength of the current in the circuit is directly proportional to the voltage at the ends of this area and inversely proportional to the resistance of the conductor. This is Ohm's law, outdoor German scientist Georg Ohm in 1827:

I=U/R,

where I is the amperage on the circuit, U is the voltage applied to the ends of the plot, R is the phase resistance.

Ohm's law is one of the fundamental laws of physics. Knowing the resistance and current, you can calculate the voltage circuit (U=IR), and knowing the amperage and voltage, you can calculate the phase resistance (R=U/I).

The resistance depends on the length of the conductor, the cross sectional area and the nature of the material. The least resistance is typical of silver and copper and ebonite and porcelain almost do not conduct electricity.

It is important to understand that the resistance of the conductor, expressed from Ohm's law formula R=U/I, is a constant. It does not depend on current or voltage. If the voltage at this area will increase several times, at the same time increase the strength of the current, and their ratio will remain unchanged.