Hameg HM1008-2 Manual

Hameg HM1008-2 Manual Manual pdf 12 page image

12 Subject to change without noticetime base is set too fast the trace may become invisible, thenreduce the time base speed.If no probe is used at least screened cable should be used,such as HZ32 or HZ34. However, this is only advisable for lowimpedance sources or low frequencies (<50 kHz). With highfrequencies impedance matching will be necessary.Non sinusoidal signals require impedance matching, preferablyat both ends. At the scope input a feed through 50 Ω-terminationwill be required. HAMEG offers a HZ22 termination. If properterminations are not used, sizeable pulse aberrations will re-sult. Also sine wave signals of > 100 kHz should be properlyterminated. Most generators control signal amplitudes only ifcorrectly terminated.HZ22 may only be used up to 7 Vrms or 20 Vpp i.e. 1 W.For probes, terminations are neither required nor allowed, theywould ruin the signal.Probes feature very low loads at fairly low frequencies: 10 MΩin parallel with few pF, valid up to several hundred kHz. How-ever, the input impedance diminishes with rising frequency toquite low values. This has to be borne in mind as probes are,e.g., entirely unsuitable to measure signals across high impe-dance high frequency circuits such as bandfilters etc.! Hereonly FET probes can be used. Use of a probe as a rule will alsoprotect the scope input due to the high probe series resistance(9 MΩ). As probes cannot be calibrated precisely enough duringmanufacturing, individual calibration with the scope input usedis mandatory! (See Probe Calibration).Passive probes will, as a rule, decrease the scope bandwidth andincrease the rise time. We recommend to use HZ200 probes inorder to make maximum use of the combined bandwidth. HZ200features 2 additional hf compensation adjustments.Whenever the DC content is > 400 V, DC coupling must be usedin order to prevent overstressing the scope input capacitor.This is especially important if a 100:1 probe is used as this isspecified for 1200 VDC + peak AC.AC coupling of low frequency signals may produce tilt.If the DC content of a signal must be blocked, it is possible toinsert a capacitor of proper size and voltage rating in front of theprobe, a typical application would be a ripple measurement.When measuring small voltages the selection of the groundconnection is of vital importance. It should be as close to voltagetake off point as possible, otherwise ground currents may de-teriorate the measurement. The ground connections of probesare especially critical, they should be as short as possible andof large diameter.STOPIf a probe is to be connected to a BNC connector usea probe tip to BNC adapter.If ripple or other interference is visible, especially at high sen-sitivity, one possible reason may be multiple grounding. Thescope itself and most other equipment are connected to safetyground, so ground loops may exist. Also, most instruments willhave capacitors between line and safety ground installed, whichconduct current from the live wire into the safety ground.First time operation and initial adjustmentsPrior to first time operation the connection between the instru-ment and safety ground must be ensured, hence the plug mustbe inserted first.Use the red POWER pushbutton to turn the scope on. Severaldisplays will light up. The scope will then assume the set upselected before it was turned off. If no trace and no readout arevisible after approximately 20 sec, push the AUTOSET button.As soon as the trace becomes visible select an average inten-sity with INTENS, then select FOCUS and adjust it, then selectTRACE ROTATION and adjust for a horizontal trace.With respect to crt life, use only as much intensity as necessaryand convenient under given ambient light conditions. When notin use, turn the intensity fully off rather than switching the scopeon and off too much as this is detrimental to the life of the crtheater. Do not allow a stationary point on the screen, it mightburn the crt phosphor.With unknown signals start with the lowest sensitivity 20 V/cm,connect the input cables to the scope, and then to the measuringobject which should be de energized beforehand. Then turn themeasuring object on. If the trace disappears, push AUTOSET.Trace rotation TRThe crt has an internal graticule. In order to adjust the deflectedbeam with respect to this graticule the Trace Rotation controlis provided. Select the function Trace Rotation and adjust for atrace which is exactly parallel to the graticule.Probe adjustment and useIn order to ensure proper matching of the probe used to thescope input impedance the oscilloscope contains a calibratorwith short rise time and an amplitude of 0.2 Vpp ± 1 %, equivalentto 4 cm at 5 mV/cm when using 10:1 probes.The inner diameter of the calibrator connector is 4.9 mm andstandardized for series F probes. Using this special connec-tor is the only way to connect a probe to a fast signal sourceminimizing signal and ground lead lengths and to ensure truedisplays of pulse signals.1 kHz – adjustmentThis basic adjustment will ensure that the capacitive at-tenuation equals the resistive attenuation thus rendering theattenuation of the probe independent of frequency. 1:1 probescan not be adjusted and need no such adjustment anyway.Prior to adjustment make sure that the trace rotation adjust-ment has been performed.Connect the 10:1 probe to the input. Use DC coupling. SetF i r s t t i m e o p e r a t i o n a n d i n i t i a l a d j u s t m e n t sincorrect correct incorrect