6
Operation
Power
To fit or replace the battery, undo the battery cover screw and lift off the cover. Fit the battery snap,
observing the correct polarity, insert the battery into the compartment and replace the cover.
WARNING!
To prevent shock hazard, all inputs must be removed before changing the battery.
Turn the instrument on by sliding the power switch on the left-hand side of the instrument to ON.
With no signal connected the display should show 0.0, the Function annunciator (default FREQ A),
and the selected measurement time annunciator flashing (default 0.3s).
Function and Measurement Time Selection
Pushing any of the keys, FREQ A, FREQ B or PERIOD A, will set the instrument to the respective
function and the selected function will be shown by annunciators in the LCD. Select the
measurement function appropriate to the signal to be measured and connect the signal to the
corresponding BNC input; the TRIG annunciator should show in the display to indicate that the
signal has been detected. Measurement time is selected by pressing the TIME key, the selected
time being shown by the appropriate annunciator in the LCD. Switching between FREQ A and
PERIOD A will immediately convert the present measurement; otherwise a change of function or
measurement time will initiate a new measurement. This may also be accomplished without a
change of function or measurement time by pressing the key corresponding to the function
currently selected; the new measurement will start immediately.
When a measurement is started, the measurement time annunciator flashes until a true result for
that selected measurement time is displayed, at which point the annunciator stays on. Further
display updates then show the running average of the signal behaviour over the last 0.3s (1
update), 1s (2 updates per second) or 10s (1 update per second) depending on the selected
measurement time. Note that if a 1s or 10s measurement time is selected, starting or restarting the
measurement gives a true result with at least 6 digits after 0.3s, followed by at least 7-digits after 1s
and, finally, at least 8-digits after 10s (if 10s measurement is selected).
The frequency and period measurement functions both produce at least 7 digits of answer per
second of measurement time and the units and decimal points are adjusted automatically to give
the answer in the most convenient units. Pressing the HOLD key will stop the measurement and
freeze the display with the
'
Hold
'
annunciator showing in the LCD. Hold may be cancelled by a
second press of the HOLD key. With the power switch in the off position pressing one of the
function keys will power the instrument on and set the selected function. The instrument will then
function normally and respond to all key presses.
After a period of about 15 seconds with no key presses the instrument will automatically power
down to conserve the battery. Switching the ON/OFF switch ON then OFF during these 15 seconds
will have no effect.
Inputs
Socket A is used for frequencies in the range
3Hz to 125MHz. Input impedance is 1M
Ω
in parallel
with 20pF. Care should be taken when measuring input signals above 350mV rms (the onset of
diode clipping) with poor signal to noise ratios as under these circumstances it is possible for noise
to generate spurious counts. To ensure a correct count, therefore, noisy signals should be
attenuated externally before being presented to the counter. A convenient attenuation factor of 10
can be achieved by the use of a x10 oscilloscope probe. The A socket will accept most types of
waveform – including sine, square and pulse signals. With pulse waveforms the mark to space ratio
should not exceed 90% and the minimum pulse width should be greater than 3ns. A low pass filter
with a cut-off frequency of 50kHz may be selected by pressing the FILTER key. The message FILT
ON shows briefly in the display and the Filt annunciator is turned on; pressing FILTER a second
time turns the filter off (display briefly shows FILT OFF and the Filt annunciator goes off). Use the
filter with low frequency large amplitude signals.
