Fluke PM6685 User manual

Connect and Go!
FLUKE PMS6SS
FLUKE

Contents
Introduction 2
Getting familiar with the front panel 4
Exercises 6
Measuring 7
Trying the front panel keys 11
Aux Menu 16
Is it really this easy? 20
4822 872 20032
Rev. 5, February 2002
©Pendulum Instruments, Sweden
Printed In Sweden

The PM6685 and PM6685R are powerful frequency coun-
ters, yet easier to use. The difference between the models
is that the PM6685R includes aRubidium timebase oscilla-
tor, an extremely accurate “atomic dock”. The PM6685R
ishoused in abigger cabinet than PM6685, but the opera-
tions of both instruments are identical. This manual gives a
brief description of some functions and keys of your new in-
strument, to get you started.
Frequency Measurements, the easy way!
Making measurements is very easy, just connect and go!
Page 2

Pw.cj.q ON &
STAND.ay^,;^
/W
Read the frequency of the signal
The counter measures immediately
AND and the settings are optimized for
your signal
GO!
If
IL
FREQA'
nnnngh.
uuuu
MW '“I auto i
TRIG '»»•*
EVEL A
1
Result Signal level
Continue to read and exercise if you want to know more
about the possibilities with this PM6685, 300 MHz Fre-
quency Counter. The 15 to 25 minutes it takes are well
spent. When you want deeper knowledge, the Operators
Manual Is there to help you.
Page 3

Getting Familiar with the Front Panel
You will reach most of the powerful features of the fre-
quency counter by pressing akey. Look at the picture be-
low and you will find the logic of the front panei.
FUNCTION SELECTION .
The FUNCTION rocker key scrolls left or ^
through the measuring functipns. 1,
The MENU key turns on all function indicoiprs on
the front panel. {Some people find It easier to use it .f^^ssuremehts., ,|
this way).
^The AUX MENU key lets you access additional ad- ^\
:,vanced,functionsv' -\
MEASURING TIME
Controls the rate i
and resplutlon of
FLUKE
INPUT SETTING KEYS
Use these keys to set the irri-V'
pedance, trigger level or sen-
sitivity, for the Ainput, or to :
select alowpass filter. The '
current, state of each setting is
shown on the display right
aboye the corresponding key.
The Cinput is fully automatic
and no. settings are required;
AUTO KEY
Apress on the
AUTO key turns
on the AUTO
function. It will
optimize the inr ,
put settings for :
.almost every ..
measurement-
DATA ENTRY KEYS
,Use these keys to
increase or de-
,
•
'crease values for 2!
measuring timb'
constants, etc; .
Press the ENTER
key to.Qonfirm
lections2®ve'ii'':;nS5
made;

MEASURED VALUE
The measured value is
displayed with ten big
clear digits
1
1|ii^ 1^ gjOVERFLOW SINGLE j
1U.U uuuuuuu“erv
FREOA FREQC PER A RATIO A/E RATIO C/A PWIDTHA TOIA-MAN.. MU.IXJE.A SIAi...S,TQ;l,
REMO'"E EXT REF CHECK FIITER 150Mii 1=03 AUTO ||LEVEL ASENSITIVITY A|i
SRQ LOBAT OVERLOAD HOLD NULL OFFSET TRIG'
—
fSS-S liSM-BiS'S S'S StS'8'|-8’^ J
BAR GRAPH INDICATOR FOR INPUT LEVEL OR SENSITIVITY
The bar graph on the display shows the signal level or sensitivity.
When AUTO is enabled the bar graph shows the signal level and
when disabled i,
The display on PM6685/pm6685R.
Page 5

Exercises
nis much more fun to push
measure. You can ^ther press ^connect
counter measure on the intern p^-cioa wia aBNC ca-
ssf&:s=s
functions.
ISet up the Generator; iFreguencYL 12 kHz {
Sauare,,...... _...!
I'50% !
I!
Ahand in the margin points out the exercises.
Basic Startup of
the Counter
ing from aknown state is always easier. To do so, just
the power off and then on again. recalls
sing local/preset and then ENTER also recalls
.14. r./rvt+inOC

Measuring
Connect the output of the generator to input Aof the coun-
ter and you wii! immediately see the measured frequency
on the display, Note the high resolution, Nine digits are dis-
played in ameasuring time of only 200 ms. The following
section is ashort description on how to use the keys and
the functions for setting the input.
Input settings
01^ AUTO function
AUTO The built-in AUTO function makes the use of PM6685 easy.
The peak to peak voltage is measured and Auto sets the
hysteresis band between 1/3 and 2/3.
You’ll soon find that it’s much easier, and more accurate to
measure with the AUTO function on, than to do manual set-
tings. There are just afew exceptions that needs manual set-
tings -AM-moduiated signals, extremely noisy signals, non-
repetitive signals, and signals with frequencies below 50 Hz.
Level meter
ILB?a.A I
Ifllllllll
lasmv IV lOVlrnis)
lllllll KNSfTftflTV A1}
lamv ISftnV *V W(tBg) ;
The bar graph scale has two functions: It shows the input
level when AUTO is on, and the sensitivity setting when
AUTO is turned off.
Ascale In Vrms is printed on the front panel. One step on
the scale equals 3dB.
Page 7

Vary the signal amplitude and watch the bar graph change.
The following figure illustrates the trigger level or sensitivity
expressed in dBm.
.Z! >am Odlim ismrn
;
I
10
lE^L A
iltilllll
nV lOomV
i,'[iaoDOPocioGyL
tv 10V(Nw41
Waveform compensation and indication
if you want to measure non-symmetrical signals, many
other counters will not trig, The reason for this is that non-
symmetrical signals do not center on OV, but they get adc
shift after the ac coupling capacitor. When the duty factor
exceeds acertaih factor, the input will stop triggering unless
the trigger window is offset to compensate for the dc shift of
the signal.
The grayed fields show the position of the hysteresis band, and
the circles are trigger points^^^ reset points
j
1ri
'riL "•---
1
ac coupling capacitor
Trigger level indica-
tion on the display
Dc shift caused by the ac coupling capacitor.
Set the symmetry on the generator to about 10% and note
that the waveform segment on the display changes. The in-
put detects the duty cycle change and compensate for the
Page 8

new waveform. Set the symmetry to the extreme opposite,
99%, and note that the counter still counts.
%Manual setting
Press the Waveform key once to turn off AUTO and return
to the last manual settings. Press the Waveform key again
to select between the three waveform compensations.
n(0 -25% duty factor)
i 1 I{25 -75% duty factor)
U(75 -100% duty factor)
Use the SENS keys to adjust the input sensitivity.
You can read the current sensitivity setting on the bar
graph. _
SENSITIVITY
THE
^!\;
\Ir/ r
Turn on AUTO, and then turn it off again by pressing one of
the SENS keys. This way you freeze the current waveform
selection and sensitivity selected by AUTO.
Pressing SENS again will increase/decrease the sensitivity
around the freezed waveform compensation.
When measuring frequency AUTO sets the sensitivity to 1/3
of the input signal level, to reject noise. When measuring
pulse width, AUTO sets the sensitivity as high as possible
to reduce trigger errors.
Lets check that by turning Auto setting to manual setting.
-Set the generator to 12 kHz sine wave and 3Vrms
(9 Vp-p) output and apply the signal to Input A.
-Select Frequency and AUTO function on the counter. No-
tice the signal level on the bar graph.
Page 9