Subject to change without notice
21
F u n c t i o n s
input A. The bandwidth for low frequencies
is as low as 10 Hz (3 dB) when the input is AC
coupled. (Input C has a fi xed AC coupling).
1:20 (pushbutton)
Selection of input signal attenuation. Pressing
this button attenuates the input signal by 26 dB
before it is applied to the input amplifi er.
Auto Trigger (AC) (pushbutton)
With Auto Trigger active the counter triggers
in the middle of the input signal. Auto Trigger
always uses AC-coupling. (AC = pushbutton
depressed).
INPUT A (BNC connector)
Signal input with a sensitivity of 20 mV
rms
up to
80 MHz and 60 mV
rms
up to 150 MHz. The input
is protected against overvoltage up to 400 V
(DC + AC
peak
).
Input impedance: 1MΩ II 40pF.
TRIGGER LEVEL (adjusting knob)
Continuously adjustment of trigger level.
TRIGGER (LED)
3 State trigger indicator. The LED fl ashes when
triggering is correct. The LED lights when the
trigger level is above the input signal level, it
is not activated when the trigger level is below
the input signal level.
8 digit display
(7 segment LEDs, 7.65 mm high)
for the measuring result (8 digit max. + expo-
nent).
Hz (LED):
Indicates the measurement of a
frequency.
Sec (LED):
Indicates the measurement of
time.
HM 8001-2:
External Gate Input (BNC connector)
Allows the measurement of the input signal,
controlled by an external source.
Triggering, measuring
and counting
Power-on test
A practical test of the correct operation of the
HM8021-4 is run automatically at power on. As
soon as power is applied, the display shows type
and version of the actual instrument and the GATE
indicator appears, LEDs are lit and the Eprom and
all functions of the counter are tested. The test
runs for about 2 seconds. If an error is detected
it is indicated by an ”I” at the leading digit and
followed by the number of the test that failed.
I
1
microprocessor RAM error
I
2
program ROM error
I
3
counting chain error
When the tests are completed satisfactorily, the
counter sets the display to zero and selects the
default measuring function A.
Measuring functions
FA/FC:
Sets the instrument to measure the
frequency of the signal connected to
input A/C.
TOT.:
The counter will totalize events
(pulses or cycles) on input A.
Measurement stops and display
freezes as soon as the input signal
is removed or DISPLAY HOLD is
depressed. Depressing RESETcluring
totalizing clearsthe display and starts
a new measurement when releasing
the button. Reset is active as long as
the switch
is depressed. Totalizing
A during External Gate is performed
applying a TTL signal to the Ext. Gate
input.
PA:
Sets the counter to measure the peri-
od duration of the signal connected to
input A.
TI
: Sets the counter to measure the
(AVG)
average pulsewidth between positive
slope and the negative slope of an
input signal at input A.
