First Time Operation And Initial Settings; Trace Rotation; Probe Adjustment And Use Of Probes; Khz Adjustment - Hameg Instruments HM 400 Manuel

Masquer les pouces

Les langues disponibles

If a probe is to be used to contact a BNC connecto, a probe

to BNC adapter should be used in order to prevent groun-

ding problems.

If ripple or noise appears on small signals at high sensitivity settings,

multiple grounds resp. ground loops may cause the problem. The mains

safety earth is quite often the cause, because other test equipment will

also be connected to the same safety earth, this can generate currents

through the shields of cables etc. Most instruments have socalled

Y capacitors connected from the mains to safety earth.

4 First time operation and initial settings

Prior to any use of the instrument make sure the power plug is inserted

before any other contacts are established.

Turn the instrument on by pressing the red button POWER, several

indicators will light up, the oscilloscope will perform a self-test. If any

errors are detected, there will be 5 acoustic signals; it is recommen-

ded to submit the instrument to a service station. After a successful

self-test the instrument will be ready to operate, it will use the settings

stored from its last use.

If there is no trace after a 20 s wait, press the AUTOSET button. If the

trace is now visible, use the SELECT button, the ADJUST + / – buttons to

ADJUST

INTENS

set the desired intensity and optimum focus. For best focus adjustment

FOCUS

it is recommended to display a full screen sine wave. If no input signal

TRACE

is connected, switch the input to GND in order to prevent any noise from

disturbing the focus adjustment.

SAVE

push long

RECALL

POSITION 1

1–6

In order to extend the life of the crt, set the intensity no higher than

needed for the specific measurement under the given ambient light

AUTOSET

conditions. Take care not to leave a bright spot as this could burn the

crt phosphor. Do not turn the instrument on and off in short intervals.

VOLTS / DIV

It is recommended to always use first the button AUTOSET and select

the buttons AC and CH 1 in the TRIGGER select area.

VAR

4.1

Trace rotation

In spite of the mumetal crt shield the earth's magnetic field still has

some inﬂuence on the crt beam. Depending on the orientation of the

instrument the trace may not always remain parallel to the graticule

lines. See the chapter Controls for the adjustment of the trace rotation.

4.2

Probe adjustment

and use of probes.

GND

Probes have to be adjusted to the

CH 1

input they are connected to; this

X-INP

adjustment has to be performed

INPUTS

each time a probe is moved to

1 MΩ II 15 pF

another input. A generator in

max.

400 V

CAT I

the HM400 delivers a fast rise time (

0.2 Vpp the frequency of which can be selected by using the knob TIME/

DIV (see the chapter Controls). The square wave signal is accessible at

the two contacts below the controls. The 0.2 V

probes, sufficient for 4 divisons at 5 mV/DIV.

4.3

1 kHz adjustment

This basic adjustment compensates for the input impedance of the

scope, the probe's capacitor is adjusted so that the capacitive division

equals the resistive division, the division will thus be identical from DC

SELECT

40 MHz ANALOG OSCILLOSCOPE

AUTO

TRIGGER

POSITION 2

LEVEL

NORM

SLOPE

VOLTS / DIV

TRIGGER

CH 1

CH 2

LINE

EXT

GND

INV

CH 2

PROBE ADJUST

1 kHz / 1 MHz

ca. 0.2 Vpp

5 ns) square wave signal of appr.

are destined for 10:1

F 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 s e t t i n g s

to high frequencies. With 1 : 1 probes or probes which can be switched

to 1 : 1, an adjustment is neither necessary nor possible. Before this

adjustment make sure the trace rotation adjustment was performed

(see TRACE rotation).

Connect the 10:1 probe to the input, e.g. CH 1, do not press any button,

set the coupling to DC, the sensitivity with VOLTS/DIV to 5 mV/DIV, the

TIME/DIV switch to 0.2 ms/DIV; make shure that both are calibrated,

i.e. the variables disabled. Connect the probe tip (and ground cable) to

the contact(s) „PROBE ADJUST" (see the photo); a 4 DIV display of two

signal periods should appear. Now adjust the probe capacitor (see the

probe manual for its location) until the square wave is perfectly ﬂat, i.e

there are neither under- nor overshoots. The transitions are invisible at

this sweep speed (see the pictures). The amplitude of the square wave

should be within 4 ±0.12 DIV.

undershoot

4.4

1 MHz adjustment

The probes supplied with the scope have additional adjustment ele-

ments which allow to correct for aberrations at high frequencies.

HM400

After this adjustment maximum bandwidth and best pulse response of

the combination scope and probe are obtained by achieving maximally

ﬂat group delay; overshoots, undershoots, ripple are minimized.

TRIG'd

This adjustment requires a fast square wave generator (

X-POSITION

output impedance (50 ohms) which delivers 0.2 V

ADJUST output of the scope fulfills these requirements.

X-MAG

x10

Connect the 10:1 probe to the input to be used. Select PROBE ADJUST

signal 1 MHz with the knob „TIME/DIV (see the chapter Controls) switch

TIME / DIV

the coupling to DC, the VOLTS/DIV selector to 5 mV/DIV and the TIME/

DIV selector to 100 ns/DIV. Connect the probe tip and ground to the two

VAR

PROBE ADJUST contacts. The square wave will now be visible and also

its rising and falling slopes. See the probe manual for the location of

the adjustment elements.

Adjustment criteria:

Only the rising slope and the top of the square wave are of concern,

disregard the other portions of the signal.

µs

.1s

.2s

–

Short rise time

HOLD

OFF

–

Clean transition from the rising slope to the top of the square

Z-INP

wave with no over- or undershoot, ﬂat top.

EXT. TRIG / Z-INP

1 MΩ II

15 pF

max.

100 V

undershoot

The amplitude of the square wave should be identical to that with the

1 kHz signal. It is important to always first perform the 1 kHz adjustment,

in general a readjustment of the 1 kHz will not be necessary. Please

note that the probe adjust frequencies are not precise and hence must

not be used for any checks of the accuracy of the time base, also their

duty cycle is not controlled.

The probe adjust signal must conform to the requirements of zero

potential at the bottom of the square wave, precise amplitude and ﬂat

tops; its frequencies and duty cycles need not be precise.

correct

overshoot

5 ns) and low

at 1 MHz; the PROBE

correct

overshoot

Subject to change without notice

Table des Matières