Snmek 1

Anglicky v odbornch pedmtech"Support of teaching technical subjects in EnglishTutorial: Mechanic - electrician

Topic: Basics of electrical engineering the 2nd. yearMeasurement of resistancePrepared by: Ing. Ji Smlek

Projekt Anglicky v odbornch pedmtech, CZ.1.07/1.3.09/04.0002je spolufinancovn Evropskm socilnm fondem a sttnm rozpotem esk republiky.

Definition of resistance:Measurement of resistanceElectrical resistance is a fundamental property of all passive and active elements :appliancescircuitsInsulation electrical equipmentThe basic unit- 1 (ohm )1 is the resistance of a conductor which passes through a current of 1 A at the ends of the conductor is 1 VRange of measured resistances in practicesmall - from 10-6 to 1 middle - from 1 to 106 large - from 106 to 1014

Slovnk:spotebiobvodizolaceZkladn jednotka Frazeologie:Elektrick odpor je zkladn vlastnost vech pasvnch a aktivnch prvk 1 je odpor vodie, kterm protk proud 1 A a na koncch vodie je napt 1 V

2Used method:Measurement of resistancesDirect method - resistance is measured by Ohmmeters showing the value measured of resistance deviation or a figure.measurement is quick and easy deflection apparatus corresponds to the size of an unknown resistance - reverse calibrated voltmetervalue Rx corresponds to the mechanical zero on the right end of the scaleelectrical zero - the left end of the scaledeflection of the hands depends on the size of voltage sources - must be zero balance - adjusted by the device

Slovnk:

Frazeologie:Pm metoda odpor se m Ohmetry udvajcmi hodnotu namenho odporu vchylkou nebo selnm dajem. men je rychl a jednoduchvchylka pstroje odpovd velikosti neznmho odporu opan cejchovan voltmetrhodnot Rx odpovd mechanick nula na pravm konci stupniceelektrick nula lev konec stupnicevchylka ruky zvis na velikosti napt zdroje nutno vyrovnat nulu justovat pstroj

3Used method:

Measurement of resistancesThe direct method - measuring the evaluative ohmmeter . is based on the magneto electrical ratio system

Direct method - measuring bridge method - Wheatstone bridgein a balanced state there does not flow a measuring diagonal current, then

Slovnk:

Frazeologie:Pm metoda men pomrovm ohmmetrem je zaloena na magnetoelektrick pomrov soustavve vyvenm stavu neprotk mc diagonlou dn proud, pak 4Used method

Measurement of resistancesComparative method- RX RVPrinciple - Distribution of voltage across the resistor in serieswe know the internal resistance of voltmeter RV

Procedurefirst we measure the voltage source U1 RX short-circuit switchthen the voltage U2 in series with V meter is connected a resistor RXvoltage is divided in proportion of resistances RV and RX

The method is suitable for resistors approximately the same size as the resistance of V-meter

Slovnk:

Frazeologie:rozdlen napt na odporech v sriiznme vnitn odpor voltmetru RV nejprve zmme napt zdroje U1 RX spojen nakrtko vypnaempak napt U2 do srie s V-metrem je zapojen rezistor RXnapt se rozdl v pomru odpor RV a RXMetoda je vhodn pro odpory piblin stejn velk jako odpor V-metru5Used method

Measurement of resistancesComparative method - for small resistances RX RVPrinciple - there is a voltage division across the resistor in series in proportion to their resistances

RN - normal resistance (specific resistance of known size)Procedurewe measure the voltage source UX we measure the voltage source UN if we measure on the same scale then the following applies :

Slovnk:Postup Frazeologie:rozdlen napt na odporech v srii v pomru jejich odporRN - odpor normlu (pesn odpor znm velikosti)zmme napt zdroje UX zmme napt zdroje UN mme-li na stejnm rozsahu pak plat:

6Used method:

Measurement of resistancesComparative method - for large resistors RX RAPrinciple - distribution of currents in parallel resistors in inverse proportion to their resistances

Procedure we measure the current resistance RXwe measure the current resistance RN if we measure on the same A- meter then the following applies:

Slovnk:Postup Frazeologie:rozdlen proud na odporech paraleln v opanm pomru jejich odporzmme proud odporem RXzmme proud odporem RN mme-li na stejnm A-metru pak plat:

7Used method:

Measurement of resistancesIndirect method - Ohm's method using Ohm's law, resistance is found by measuring current and voltage drop over the resistorThe resistance is calculated from Ohm's law according to the formula circuit for measuring small resistances

b) circuit for measuring large resistances

Slovnk:

Frazeologie:Nepm metoda Ohmova metoda s pouitm Ohmova zkona se odpor zjist zmenm proudu a bytku napt na rezistoruOdpor se vypote z Ohmova zkona dle vzorce zapojen pro men malch odporzapojen pro men velkch odpor8Used method:

Measurement of earth resistanceIndirect method - Wenner method - measuring the voltage drop Used in practise: great importance to work safety the size of earth resistance depends on the emergence of a potential dangerous contact voltage with the structure of appliancesearth resistance is the resistance between the earthing and the groundground resistance is an earth resistance earthing including resistance of ground leads - entire ground distribution

Principle methodsthe voltage drop occurs only in the vicinity of earth electrodesin the space between the ground electrode is a large cross-section - there is no voltage dropThe resistance of earth electrodes is calculated:

Slovnk:

Frazeologie:velk vznam pro bezpenost prce zemn odpor je pechodov odpor mezi zemniem a zemodpor uzemnn je zemn odpor zemnie vetn odporu zemnch svod celho zemnho rozvoduOdpor zemni se vypot:

9Describe what it is electrical resistance Write what methods can measure el.resistance direct

indirect

Describe what is different in the comparison methods for measuring of large and small resistancesLarge resistances -Small resistances -

Activities for students questions

Slovnk:velk odpory mal odpory -

Frazeologie:Popi so to je elektrick odporNapi jakmi metodami lze zmit el.odporPopi v em se li porovnvac metoda pro men velkch a malch odpor

10Write the measurement procedure for resistance in a V- meter with comparative method for RV RX Describe what is the principle of Ohms method for measurement of resistance Explain why when there is a greater distance from the earthing there is no voltage drop, even when going through the earth is an el. currentActivities for students questions

Slovnk:

Frazeologie:Napi postup men odporu V-metrem porovnvac metodou pi RX RVPopi jak je princip Ohmovy metody men odporuVysvtli pro ve vt vzdlenosti od zemnie nedochz k bytku napt, i kdy prochz zem el.proud

11Muk, J. Management ve vzdlvn dosplch. Praha: EUROLEX BOHEMIA, 2000. ISBN 80-7361-269-7.Operan program Vzdlvn pro konkurenceschopnost, ESF 2007 2013.Dostupn na: http://www.msmt.cz/eu/provadeci-dokument-k-op-vzdelavani-pro-konkurenceschopnostUebnice Elektrick men Ing. Pavel Vylegala, SE Ostrava, 2006Uebnice Elektrick men SNTL, 1981Elektrotechnika - Laboratorn cvien pro bakalsk studium - Doc. Ing. Milo Hammer, CSc.

Bibliography