Hameg HM 2005 Manual 

Hameg HM 2005 Manual  Manual pdf 30 page image

Subject to change without notice30In such cases it is recommended to select normal triggering andto set the trigger point approx. 0.5div above or below the trace.If under one of these conditions the trigger indicator LED is lit,this indicates the presence of a signal. Then both the timecoefficient and Y deflection coefficient should be reduced. Pleasenote that a reduction in intensity may occur, which could resultin a blank screen when the physical limits are reached.Mean Value DisplayThe DC Mean Value of the input voltage is displayed in place ofthe CURSOR line measurement, if the CURSOR measurementfunction is not activated. MEAN VALUE ON must activated underMISCELLANEOUS (submenu of SETUP) and further conditionsmet.The signal to be measured (AC > 20 Hz) must be applied at inputCH I or CH II with its DC content at the input (i.e. DC couplingrequired). Yt (time base) mode and internal triggering (triggersource CH I or CH II; not alternated triggering) must be used. ACor DC trigger coupling must be selected. If the above conditionsare not met, “DC:?” will be displayed.The mean value is acquired using the internal trigger signalamplifiers. With the exception of DUAL mode, the indicated meanvalue is automatically related to the active channel (CH I or CHII), as the channel selection also selects the assigned triggeramplifier. In DUAL mode one can select between trigger amplifierCH I or CH II for triggering. Thus the indicated mean value refersto the channel from which the trigger signal originates.The DC mean value is displayed with an algebraic sign (e.g. “DC:501mV” or “DC: -501mV). Overranging is indicated by “ < “ or “> “ sign (e.g. “DC<1.80V” or “DC>1.80V”). Being dependent ona necessary time constant for mean value creation, the displayupdate requires a few seconds after a voltage change.The reading accuracy is dependent on the instrumentspecifications (vertical deflection tolerance max. 3% from 5mV/div. to 20V/div.). Although the tolerances are significantly smallerin reality, other deviations such as unavoidable offset voltagesmust be taken into account, which may cause a display deviatingfrom 0 Volt without signal applied at the input.The display shows the arithmetic (linear) mean value. The DCcontent is displayed if DC or DC with superimposed AC voltagesare applied. In the case of square wave voltages, the mean valuedepends on the pulse duty factor.Component TesterGeneralThe instrument specific information regarding the control andterminals are part ofitem (42) in section“Controls and Readout”.The instrument has a built-in electronic Component Tester, whichis used for instant display of a test pattern to indicate whether ornot components are faulty. It can be used for quick checks ofsemiconductors (e.g. diodes and transistors), resistors,capacitors, and inductors. Certain tests can also be made tointegrated circuits. All these components can be testedindividually, or in circuit provided that it is unpowered. The testprinciple is fascinatingly simple. A built-in generator delivers asine voltage, which is applied across the component under testand a built-in fixed resistor. The sine voltage across the test objectis used for the horizontal deflection, and the voltage drop acrossthe resistor (i.e. current through test object) is used for verticaldeflection of the oscilloscope. The test pattern shows a current-voltage characteristic of the test object.The measurement range of the component tester is limited anddepends on the maximum test voltage and current (please notedata sheet). The impedance of the component under test is limitedto a range from approx. 20Ω to 4.7kΩ. Below and above thesevalues, the test pattern shows only short-circuit or open-circuit.For the interpretation of the displayed test pattern, these limitsshould always be born in mind. However, most electroniccomponents can normally be tested 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-circuit measurementsare to be carried out. For the component connection, two simpletest leads with 4mm Ø banana plugs, and with test prod, alligatorclip or sprung hook, are required.The test leads are connected as described in section “Controlsand Readout”.Caution!Do not test any component in live circuitry. Remove allgrounds, power and signals connected to the componentunder test. Set up Component Tester as stated. Connecttest leads across component to be tested. Observe oscil-loscope display.IMPORTANT: Only discharged capacitors should be testet!Test Pattern DisplaysThe “Test patterns” shows typical patterns displayed by thevarious 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 expected froma resistor is therefore a sloping straight line. The angle of slope isdetermined by the resistance of the resistor under test.With high values of resistance, the slope will tend towards thehorizontal axis, and with low values, the slope will move towardsthe vertical axis. Values of resistance from 20Ω to 4.7kΩ can beapproximately evaluated. The determination of actual values willcome with experience, or by direct comparison with a componentof a known value.Testing Capacitors and InductorsCapacitors and inductors cause a phase difference betweencurrent and voltage, and therefore between the X and Y deflection,Mean Value Display