Hameg HM404-2.02 Manual

Hameg HM404-2.02 Manual Manual pdf 29 page image

29Subject to change without noticeAuto Set Mean Value DisplayAttention:In combination of chopped DUAL mode and high ex-pansion ratios in DELAY mode, chop interference maybe visible. This can be overcome by selecting alternateDUAL mode by briefly pressing simultaneously CHIand DUAL buttons.AUTO SETThe instrument specific information regarding this function ispart of the section ”Controls and Readout” paragraph AUTOSET (2). As also mentioned in that section all controls areelectronically selected with the exception of the POWER andcalibrator frequency (CAL 1kHz/1MHz) pushbuttons as wellas the FOCUS and TR (trace rotation) control.Thus automatic signal related instrument set up in Yt (timebase) mode is possible. In most cases no additional manualinstrument setting is required.Briefly pressing the AUTO SET pushbutton causes theinstrument to switch over to the last Yt mode settingsregarding CH I, CH II and DUAL. If the instrument wasoperated in Yt mode, the actual setting will not be affectedwith the exception of ADD mode which will be switched off.At the same time the attenuator(s) (VOLTS/DIV) areautomatically set for a signal display height of approx. 6 divin mono channel mode or if in DUAL mode for approx. 4 divheight for each channel. This and the following explanationregarding the automatic time coefficient setting assumes thatthe pulse duty factor of the input signal is approx. 1:1.The time deflection coefficient is also set automatically for adisplay of approx. 2 signal periods. The time base settingoccurs randomly if complex signals consisting severalfrequencies e.g. video signals are present. If cursor voltagemeasurement is selected, AUTOSET also affects the positionof the CURSOR lines. Please note AUTOSET (2) in section”Controls and Readout”.AUTO SET sets the instrument automatically to the followingoperating conditions: AC or DC input coupling unalteredor in GD condition the previously used setting Internal triggering (channel I or channel II) Automatic peak (value) triggering Trigger level in electrical midrange position Y deflection coefficient(s) calibrated Time base deflection coefficient calibrated AC trigger coupling (except DC trigger coupling) SEARCH and DELAY time base mode switched off X x10 magnifier switched off Automatic X and Y position settings Trace and readout visible.If DC trigger coupling had been selected, AC trigger couplingwill not be chosen and the automatic trigger is operativewithout the peak value detection.The X position is set to the CRT center as well as the Y positionin CH I or CH II mode. In DUAL mode the channel I trace isset to the upper half and the channel II trace to the lower halfof the CRT.The 1mV/div and 2mV/div deflection coefficient will not beselected by AUTO SET as the bandwidth is reduced on thesesettings.Attention!If a signal is applied with a pulse duty factor of approx.400:1 or larger, an automatic signal display can not beperformed. The pulse duty factor causes too low a Ydeflection coefficient (sensitivity too high) and toohigh a time deflection coefficient (time base speed toslow) and results in a display in which only the base-line is visible.In such cases it is recommended to select normal triggeringand to set the trigger point approx. 0.5div above or below thetrace. If under one of these conditions the trigger indicatorLED is lit, this indicates the presence of a signal. Then both thetime coefficient and Y deflection coefficient should be reduced.Please note that a reduction in intensity may occur, whichcould result in a blank screen when the physical limits arereached.Mean Value Display.The DC Mean Value is displayed in place of the cursor linemeasurement, if the cursor lines are switched off, MEANVALUE ON is activated in the menu MISCELLANEOUS(submenu of SETUP) and further conditions are met:The signal to be measured (AC > 20 Hz) must be applied atinput CH I (26) or CH II (30) with its DC content at the measuringamplifier; DC input coupling (27) (31) required. Yt (time base)mode in combination with internal triggering (trigger sourceCH I or CH II; not alternated triggering) must be present. AC-or DC- trigger coupling must be selected.If the aforementioned conditions are not met, “DC:?” will bedisplayed.The mean value is acquired using the trigger signal amplifiersfor internal triggering. With the exception of DUAL mode, theindicated mean value is automatically related to the activechannel (CH I or CH II), as the channel selection also selectsthe assigned trigger amplifier. In DUAL mode one can selectbetween trigger amplifier CH I or CH II for triggering. Theindicated mean value refers to the channel from which thetrigger signal originates.The DC mean value is displayed with an algebraic sign (e.g.“DC: 501mV” resp. “DC: -501mV). Overranging is indicatedby “ < “ resp. “ > “ sign (e.g. “DC<1.80V” resp. “DC>1.80V”).Being dependent on a necessary time constant for mean valuecreation, the display update requires a few seconds after avoltage change.The reading accuracy is dependent on the instrumentspecifications (vertical deflection tolerance max. 3% from 5mV/div. to 20V/div.). Although the tolerances are significantlysmaller in reality, other deviations such as unavoidable offsetvoltages must be taken into account, which may cause adisplay deviating from 0 Volt without signal applied at the input.The display shows the arithmetic (linear) men value. The DCcontent is displayed if DC or AC superimposed DC voltagesare applied. In case of square wave voltages, the mean valuedepends on the pulse duty factor.