Hameg HM 407A Manual

27Subject to change without noticevoltage point on the trigger signal (trigger point), by theadjustment of the trigger level control. The control rangedepends on the peak to peak value of the signal. This triggermode is therefore called Automatic Peak (Value)- Triggering.Operation of the scope needs only correct amplitude and timebase settings, for a constantly visible trace. Automatic modeis recommended for all uncomplicated measuring tasks.However, automatic triggering is also the appropriate operationmode for the “entry” into difficult measuring problems, e.g.when the test signal is unknown relating to amplitude, frequencyor shape. Presetting of all parameters is now possible withautomatic triggering; the change to normal triggering canfollow thereafter.The automatic triggering works above 20Hz. The failure ofautomatic triggering at frequencies below 20Hz is abrupt.However, it is not signified by the trigger indicator LED this is stillblinking. Break down of triggering is best recognizable at the leftscreen edge (the start of the trace in differing display height).The automatic peak (value) triggering operates over all variationsor fluctuations of the test signal above 20Hz. However, if thepulse duty factor of a square-wave signal exceeds a ratio of100:1, switching over to normal triggering will be necessary.Automatic triggering is practicable with internal and externaltrigger voltage.Normal TriggeringInformation specific to the instrument are given in the articlesNM - AT (15), LEVEL (17) and TRIG. MODE (26) in the section”Controls and readout”. The time fine adjustment (VAR.) andthe hold off time setting assist in triggering under speciallydifficult signal conditions. The following description refers tothe Yt (time base) analog mode.With normal triggering, the sweep can be started by AC signalswithin the frequency range defined by the trigger couplingsetting.In the absence of an adequate trigger signal or when the triggercontrols (particularly the trigger LEVEL control) are misadjusted,no trace is visible, i.e. the screen completely blanked.When using the internal normal triggering mode, it is possibleto trigger at any amplitude point of a signal edge, even withvery complex signal shapes, by adjusting the trigger LEVELcontrol. If the signal applied at the Y input is used for triggering(internal trigger source), its adjusting range is directly dependenton the display height, which should be at least 0.5div. If it issmaller than 1div, the trigger LEVEL adjustment needs to beoperated with a sensitive touch. In the external normal triggeringmode, the same applies to approx. 0.3Vpp external triggervoltage amplitude.Other measures for triggering of very complex signals are theuse of the time base variable control and HOLD OFF timecontrol, hereinafter mentioned.(Slope)Please note item (15)in section “Controls and readout” forinstrument specific information.The actual slope setting is displayed in the readout. The settingis not changed by the AUTOSET function. The slope settingcan be changed in delay mode for the delay time base triggerunit if the delay trigger function is active. The previous slopesetting for the undelayed time base trigger is stored and stillactive.For further information please note “Controls andreadout”.The time base generator can be triggered by a rising or fallingedge of the test signal. Whether the rising or the falling edgeis used for triggering, depends on the slope direction setting.This is valid with automatic and normal triggering. The positiveslope direction means an edge going from a negative potentialand rising to a positive potential. This has nothing to do withzero or ground potential and absolute voltage values. Thepositive slope may also lie in a negative part of a signal.However the trigger point may be varied within certain limitson the chosen edge using the LEVEL control. The slopedirection is always related to the input signal and the noninverted display.Trigger couplingInstrument specific information regarding this item can benoted in the “Data Sheet”.The coupling setting ( TRIG. MODE(26))and indication are described under “Controls and readout”.As the automatic triggering does not work below 20Hz, normaltriggering should be used in DC and LF trigger coupling mode.The coupling mode and accordingly the frequency range of thetrigger signal should meet the signal requirements.AC: This is the most frequently used trigger mode. Thetrigger threshold increases below and above thefrequency limits mentioned in the data sheet. This filtercuts off both the DC content of the trigger signal and thelowest frequency range.DC: In this coupling mode the trigger signal is coupledgalvanically to the trigger unit. Therefore there is no lowfrequency limit.DC triggering is recommended if the signal is to betriggered with quite slow processes or if pulse signalswith constantly changing pulse duty factors have to bedisplayed.HF: In this coupling mode the transmission range equals ahigh pass filter. It cuts off the DC content of the triggersignal and the lower frequency range.LF: LF trigger coupling has a low pass filter characteristic. Asin DC trigger coupling, there is no low limit for the passfrequency range (galvanic coupling) in connection withnormal triggering. The trigger signal is coupled througha capacitor in the automatic (peak value) triggering andLF trigger coupling. This results in a low frequency limitwhich , however, does not disturb as the limit is belowthe repetition frequency of the trigger automatic.The LF trigger coupling is often more suitable for lowfrequency signals than DC trigger coupling because thenoise components of the trigger signals are stronglysuppressed. This avoids or reduces , under borderlineconditions, jitter or double traces especially with verylow signal voltages. The trigger threshold raisescontinuously above the pass band.TV-L: The built-in active TV-Sync-Separator provides theseparation of line sync pulses from the video signal. Evendistorted video signals are triggered and displayed in astable manner. This mode is described under paragraph“Triggering of video signals”.TV-F: The built-in active TV-Sync-Separator also provides theseparation of frame sync pulses from the video signal.Even distorted video signals are triggered and displayedin a stable manner. This mode is described underparagraph “Triggering of video signals”.Triggering and time base