Hameg HM 407A Manual

19Subject to change without noticeNone of these will appear in the readout in undelayed timebase operation.When ”SEA”, ”DEL” or ”DTR” mode is effective, pressingand holding the button switches over to undelayed timebase.Provided that neither ”SEA” nor ”DEL” resp. ”DTR” areactive, the following description assumes that:1.X-MAG. x10 is switched off,2.the trace starts on the left vertical graticule line and3.the part of signal to be expanded must be displayedwithin the (horizontal) range 2 up to 6 divisions aftertrace start position.SEAIn SEA. (SEARCH)mode, the hold off time is automaticallyset to minimum and for the first few divisions the traceis blanked. The trace will then be unblanked. The point atwhich the trace starts can be varied with DEL.POS (fineadjustment) from about 2 to 6 divisions. The blankedsection serves as a guide to the delay time. The delay timeis based on the current time deflection coefficient settingand can also be coarsely set with the TIME/DIV control(range: 20ms to 100ns).DELPressing the button briefly switches over from ”SEA” to”DEL” (DELAY) mode. Now the trace starts at the leftvertical graticule line, beginning with that part of thesignal that was previously unblanked first when ”SEA”was active. From that position, the signal display can beexpanded in the X-direction by rotating the TIME/DIVcontrol clockwise and thus decreasing the time deflectioncoefficient. If a part of the signal of interest goes beyondthe right edge, it can be brought within the screen andmade visible by DEL.POS knob. Increasing the timedeflection coefficient beyond that used in the ”SEA”(SEARCH) mode is not possible.In the untriggered ”DEL” (DELAY) mode, a trigger eventdoes not start the trace at once but only starts the delaytime. After the delay time has elapsed the trace is started.DTRIn triggered DELAY mode (DTR), to start the sweep, asignal suitable for triggering must appear after the delaytime. The trace will be started if the instrument settings(e.g. LEVEL setting) enable a triggering.See DEL.TRIG.- VAR. (30).(30) DEL.TRIG. - VAR. - Pushbutton with two functionsThe pushbutton is operative only in analog mode.In the case of untriggered ”DEL” (DELAY) mode (29),briefly pressing the button switches over to ”DTR”(triggered DELAY mode). Thereby, the previously activesettings, Automatic/normal triggering (15), triggerLEVEL (17), trigger slope (15) and trigger coupling(26) will be stored.The instrument will be automatically switched to normaltriggering (NM) and DC trigger coupling in ”DTR” mode.Subsequently the trigger LEVEL setting and the triggerslope should be so adjusted that the signal for delayedtrigger can trigger the time base. Without triggering thescreen will remain blank.Briefly pressing the button again switches back to(untriggered) DEL. operation.VAR.Pressing and holding the pushbutton changes the functionof the TIME/DIV. knob.The TIME/DIV. knob (28) can function as a time deflectioncoefficient switch (1-2-5 sequence) or as a time vernier(fine adjustment). The current function is indicated by theVAR-LED. The TIME/DIV. knob functions as a vernierwhen the VAR-LED is switched on, but the time basesetting remains calibrated until the (vernier) knob isoperated. The readout now indicates ”T>...” instead of”T:...”. Rotating further anticlockwise increases the timedeflection coefficient (uncalibrated) until the maximum isreached indicated by a beep. Rotating the knob clockwisehas the opposite effect. Now, the vernier is again in thecalibrated position and the symbol ” >” will be replacedby symbol ” :”.The function of the knob can be switched back to normal(calibrated) time base, pressing and holding the button.Underneath the front panel sector described above, theBNC sockets and four pushbuttons are located.(31) INPUT CH I - (HOR. INP. (X)) - BNC socket.This BNC socket is the signal input for channel I (INPUTCH I). In XY mode, signals at this input are used for the X-deflection. The outer (ground) connection is galvanicallyconnected to the instrument ground and consequently tothe safety earth contact of the line/mains plug.(32) AC / DC - Pushbutton with two functions.Input coupling:Briefly pressing this pushbutton switches over from AC(~ symbol) to DC (= symbol) input coupling and vice versa,if the input is not switched to GD (33). The AC/DC settingis displayed in the readout with the deflection coefficient.Probe factor:Pressing and holding the pushbutton selects the indicateddeflection coefficient of channel I displayed in the readout,between 1:1 and 10:1. In condition 10:1 the probe factoris thus indicated by a probe symbol displayed by thereadout in front the channel information (e.g. “probesymbol”, Y1...). In the case of cursor voltage measu-rement, the probe factor is automatically included.Controls and readout