Hameg HM1008-2 Manual

Hameg HM1008-2 Manual Manual pdf 19 page image

19Subject to change without noticeAUTOSETFor specific information consult ”Controls and Readout“AUTOSET 11 .The following description is valid for both analog and digitalmode. AUTOSET does not change from analog to digital modeor vice versa. If in digital mode the modes ”Roll“, ”Envelope“ or”Average“ (ACQUIRE) are present or the trigger mode „Single“(MODE) is selected, theses modes will be switched off as AU-TOSET always switches to ”Refresh“ acquistion. The signal tobe displayed must meet the amplitude and frequency require-ments of automatic triggering, to enable a useful automaticinstrument setting.All controls except for the POWER switch are electronicallyscanned, all functions can also be controlled by the microcom-puter, i.e. also via the interfaces.This is a precondition for AUTOSET as this function must be ableto control all functions independent of control settings. With theexception of FFT, AUTOSET will always switch to YT mode, butpreserve the previous selection of CH1, CH2 or dual trace; ADDor XY modes will be switched to dual trace Yt.AUTOSET helps in combination with FFT to avoid scaling pro-blems and ensures that the signal height is within A/D converterlimits.Automatic setting of the vertical sensitivities and the time basewill present a display within 6 cm height (4 cm per signal in dualtrace) and about 2 signal periods. This is true for signals notdiffering too much from a 1:1 duty cycle. For signals containingseveral frequencies like video signals the display may vary.Initiating the AUTOSET function will set the following operatingconditions:– last selection of ac or DC coupling– internal triggering– automatic triggering– automatic trigger source selection– trigger level set to the center of its range– calibrated Y sensitivities– calibrated time base– AC or DC trigger coupling unmodified– HF trigger coupling switched to DC– LF or Noise Reject filters left– X magnifi er switched off– Y and X positioning automaticPlease note:For pulse signals with duty cycles approaching 400:1 no au-tomatic signal display will be possible.In such cases switch to normal trigger mode and set the triggerposition about 5 mm above the centre. If the trigger LED lightsup, a trigger is generated and the time base is operating. Inorder to obtain a visible display it may be necessary to changethe time base and V/DIV settings. Depending on the duty cycleand the frequency, the signal may still remain invisible. Thisapplies only to analog mode. In digital mode the trace is alwaysof equal brightness because not the actual signal is shown,but a low frequency construction of it. Also there is no storedinformation about the trace intensity.C o m p o n e n t T e s t e rComponent TesterSpecific information can be found in ”Controls and Readout“ un-der COMPONENT/PROBE 40 and COMPONENT TESTER 41 .The scope has a built in component tester. The test object is con-nected with 4 mm banana plugs. In this mode the Y amplifiersand the time base are turned off. If the components are part of acircuit this must be de energized and disconnected from safetyground. Except for the two test leads there must be no furtherconnection between scope and component. (See ”Tests within acircuit“). As described in section ”Safety“ all ground connectionsof the scope are connected to safety ground including those ofthe component tester. As long as individual components aretested this is of no consequence.The display can only be affected by the controls contained inthe FOCUS/TRACE menu: A-Int., Focus, Trace rotation, HORI-ZONTAL position.If components are to be tested which are part of a circuit oran instrument they must first be de energized. If they are con-nected to the mains they must be unplugged. This will preventa connection between scope and circuit via the safety groundwhich may affect the measurement.STOPDo not test charged capacitors.The principle of the test is very simple: a sine wave generatorwithin the scope generates a 50 Hz ±10 % voltage which isapplied to a series connection of the test object and a resistorwithin the scope. The sine wave proper deflects in X direction,the voltage across the resistor which is proportional to the testcurrent deflects in Y direction.If the object contains neither capacitors nor inductors, there willbe no phase shift between voltage and current, so a straightline will show up which will be more or less slanted, dependingon the value of the object’s resistance, covering approx. 20 Ωto 4.7 kΩ. If there is a short circuit, the trace will be vertical,i.e. (almost) no voltage produces a high current. A horizontalline will thus indicate an open circuit: there is only voltage butno current.Capacitors or inductors will create ellipses. The impedancemay be calculated from the ellipse’s geometric dimensions.Capacitors of approx. 0.1 μF to 1000 μF will be indicated.– An ellipse with its longer axis horizontal indicates a highimpedance (low capacitance or high inductance)– An ellipse with its longer axis vertical will indicate a lowimpedance (high capacitance or low inductance)– A slanted ellipse will indicate a lossy capacitor or inductor.Semiconductors will show their diode characteristics, however,only 20 Vpp are available, so the forward and reverse characte-ristics can only be displayed up to 10 Vp in each direction. Thetest is a two terminal test, hence it is not possible to measuree.g. the current gain of a transistor. One can only test B-C, B-E,and C-E. The test current is only a few mA, so the test will notharm ordinary semiconductors. (Sensitive devices like delicatehf transistors etc. should not be tested). The limitation to 10 Vpwith bipolar transistors will usually suffice as common defectswill show up.The best method to verify whether a componentis defective is comparison to a good one. If the lettering of a