31
- if the test point shows a level between 30% and 70% of Vcc, then “--
-” appears in the display
To establish the logic level or to set the level ranges, proceed as follows:
a) Switch the measuring instrument on. The initial configuration is
always AC voltage measurement in “AUTO” (automatic range selec-
tion) mode. Now press the „Hz•hfe•
•Logic“ button four times.
The measuring instrument switches to logic test, recognisable
through the symbol “Logic” at the bottom of the display and through
the display of the voltage in V in the centre of the sub-display and of
the frequency in kHz on the right of the sub-display. Additionally, to
the left of the voltage indication “t” can be seen with the TTL level,
with “CMOS 3V” => “3C” and with “CMOS 5V” => “5C”.
b) Connect the black test lead to the “COM” measuring instrument
socket and the red test lead to the „V•
½
•Hz•Logic•->I-“ socket.
c) The bar graph beneath the measured value is active during measure-
ment, being similar to an analogue indicator with a faster reaction
time. The bar graph operates as a trend indicator.
d) Now connect the other end of the black test lead (test probe) to the
“earth” of the digital circuit, normally “-”.
e) While the black test lead remains connected to “earth”, touch the
points to be tested with the red test probe.
5.11 Use as signal generator (not VC 630)
The DMM incorporates a sort of “function generator”, which delivers
from the centre measurement socket a frequency variable between the
limits 1 Hz and 5 (5.041) kHz at the fixed level of 5V.
To output a TTL level at a frequency variable within these limits, proceed
as follows:
a)
Switch the measuring instrument on. The initial configuration is
always AC voltage measurement in “AUTO” (automatic range selec-
tion) mode. Now press the„Hz•hfe•
•Logic“ button twice. The
30
- no transistor can be measured which is incorporated into a circuit.
- the hfe values of FETs or other unipolar transistors cannot be measu-
red with this multimeter.
- when the connecting “legs” of the item to be measured do not fit
into the socket (too “fat”), do not use force, otherwise the socket can
thereby be damaged.
- the measurement of hfe reacts to temperature variations. As soon as
the transistor is picked up and plugged into the connector and war-
med with the fingers, the measured value can alter. If an unstable dis-
play occurs, remove the transistor and allow it to cool down to room
temperature.
Notes!
1. During transistor tests, in addition to the measured value only the
bar graph is also displayed. The sub-displays are not active.
2. Selectable special functions
The following sub-functions, according to multimeter model, are sel-
ectable by means of the “ENTER MENU” button:
“
Æ
%” reference value measurements, “MIN/MAX” value capture,
“TIME”, “REC” record measured value, “RCLL” measured value recall,
“LMT” comparison function (VC 670 only) and “PH” peak value mea-
surement (VC 650 and VC 670 only). These sub-functions are descri-
bed in more detail in section 5.12.
5.10 Logic test (not VC 630)
This measurement function is used to establish the logic levels in digital
circuits (27-TTL, 3 V or 5 V logic and others). With this logic function the
following conditions can be determined:
- if the test point shows a high level greater than 70 % of Vcc then “Hi”
appears in the display.
- if the test point shows a low level, smaller than 30 % of Vcc, then
“Lo” appears in the display.
