Hameg HM404-2.02 Manual

Hameg HM404-2.02 Manual Manual pdf 30 page image

Subject to change without notice30Component TesterComponent TesterGeneralThe instrument specific information regarding the control andterminals are part of item (39) in section ”Controls and Readout”.The instrument has a built-in electronic Component Tester,which is used for instant display of a test pattern to indicatewhether or not components are faulty. It can be used for quickchecks of semiconductors (e.g. diodes and transistors),resistors, capacitors, and inductors. Certain tests can also bemade to integrated circuits. All these components can betested individually, or in circuit provided that it is unpowered.The test principle is fascinatingly simple. A built-in generatordelivers a sine voltage, which is applied across the componentunder test and a built-in fixed resistor. The sine voltage acrossthe test object is used for the horizontal deflection, and thevoltage drop across the resistor (i.e. current through testobject) is used for vertical deflection of the oscilloscope. Thetest pattern shows a current-voltage characteristic of the testobject.The measurement range of the component tester is limitedand depends on the maximum test voltage and current(please note data sheet). The impedance of the componentunder test is limited to a range from approx. 20Ω to 4.7kΩ.Below and above these values, the test pattern shows onlyshort-circuit or open-circuit. For the interpretation of thedisplayed test pattern, these limits should always be born inmind. However, most electronic components can normally betested without any restriction.Using the Component TesterAfter the component tester is switched on, the verticalpreamplifier and the time base generator are inoperative. Ashortened horizontal trace will be observed. It is not necessaryto disconnect scope input cables unless in-circuitmeasurements are to be carried out.For the component connection, two simple test leads with4mm Ø banana plugs, and with test prod, alligator clip orsprung hook, are required. The test leads are connected asdescribed in section ”Controls and Readout”.Test ProcedureCaution!Do not test any component in live circuitry - remove allgrounds, power and signals connected to the compo-nent under test. Set up Component Tester as stated.Connect test leads across component to be tested.Observe oscilloscope display.Only discharged capacitors should be tested!Test Pattern DisplaysThe page ”Test patterns” shows typical patterns displayed bythe various components under test.• Open circuit is indicated by a straight horizontal line.• Short circuit is shown by a straight vertical line.Testing ResistorsIf the test object has a linear ohmic resistance, both deflectingvoltages are in the same phase. The test pattern expectedfrom a resistor is therefore a sloping straight line. The angleof slope is determined by the resistance of the resistor undertest. With high values of resistance, the slope will tendtowards the horizontal axis, and with low values, the slope willmove towards the vertical axis. Values of resistance from 20Ωto 4.7kΩ can be approximately evaluated. The determinationof actual values will come with experience, or by directcomparison with a component of a known value.Testing Capacitors and InductorsCapacitors and inductors cause a phase difference betweencurrent and voltage, and therefore between the X and Ydeflection, giving an ellipse-shaped display. The position andopening width of the ellipse will vary according to theimpedance value (at 50Hz) of the component under test.A horizontal ellipse indicates a high impedance or a relativelysmall capacitance or a relatively high inductance.A vertical ellipse indicates a small impedance or a relativelylarge capacitance or a relatively small inductance.A sloping ellipse means that the component has a considerableohmic resistance in addition to its reactance.The values of capacitance of normal or electrolytic capacitorsfrom 0.1μF to 1000μF can be displayed and approximatevalues obtained. More precise measurement can be obtainedin a smaller range by comparing the capacitor under test witha capacitor of known value. Inductive components (coils,transformers) can also be tested. The determination of thevalue of inductance needs some experience, because inductorshave usually a higher ohmic series resistance. However, theimpedance value (at 50Hz) of an inductor in the range from20Ω to 4.7kΩ can easily be obtained or compared.Testing SemiconductorsMost semiconductor devices, such as diodes, Z-diodes,transistors, FETs can be tested. The test pattern displays varyaccording to the component type as shown in the figuresbelow. The main characteristic displayed during semiconductortesting is the voltage dependent knee caused by the junctionchanging from the conducting state to the non conductingstate. It should be noted that both the forward and the reversecharacteristic are displayed simultaneously. This is a two-terminal test, therefore testing of transistor amplification isnot possible, but testing of a single junction is easily andquickly possible. Since the test voltage applied is only verylow, all sections of most semi-conductors can be testedwithout damage. However, checking the breakdown or reversevoltage of high voltage semiconductors is not possible. Moreimportant is testing components for open or short-circuit,which from experience is most frequently needed.Testing DiodesDiodes normally show at least their knee in the forwardcharacteristic. This is not valid for some high voltage diodetypes, because they contain a series connection of severaldiodes. Possibly only a small portion of the knee is visible.Zener diodes always show their forward knee and, dependingon the test voltage, their zener breakdown forms a secondknee in the opposite direction. If the breakdown voltage ishigher than the positive or negative voltage peak of the testvoltage, it can not be displayed.