Tektronix DC 5010 Anleitung Seite 38

Operating Instructions-DC SO 10
Connecting External and Internal Signal Sources
The DC 5010 can be used to measure input signals to
either channel from the front panel. The SLOPE, TERM,
ATTEN, and COUPL pushbuttons are effective in condition-
ing the signal.
If a high impedance signal probe is to be used between
the front panel bnc connectors and the measurement
source, use a probe capable of compensating for the input
capacitance of the counter (less than 24 pF). A probe is
recommended for all digital logic applications; the
TEKTRONIX P6125 has been designed specifically for these
counters, and its use is recommended. The counter has
been designed, however, to properly trigger on ECL signals
even when a XI0 attenuator probe is used.
Input Coupling, Noise, and Attenuation
You can use either the ac coupling (AC COUPL) or dc
coupling (DC COUPL) mode to couple the input signal to the
CHANNEL A or CHANNEL B input amplifiers. If the signal to
be measured is riding on a dc level, its amplitude limits may
not fall within the triggering level range. The AC COUPL
mode should be used for repetitive signals having a fixed
frequency and a constant duty cycle, or for signals riding on
a large dc level. Slope selection is relatively unimportant
when measuring the frequency or period of sine-waves. The
50
Q
Termination is selected for high frequency 50
Q
sys-
tems, while 1 Mil is selected for high impedance probes and
I
Noise
for other high impedance situations. When in 50 Q , the inter-
nal termination resistor could be damaged if tlhe user acci-
,
dentally applied an overly large signal. To prevent this, the
DC 501 0 automatically reverts to 1 MQ for most signals that
might damage the 50 8 resistor. See the Specification sec-
tion for more detail.
If the signal frequency or duty cycle changes, the trigger-
ing point may shift, stopping the measurement process. Use
the DC COUPL mode for low frequency ac signals, signals
with a low duty cycle, and during any time interval measure-
ment (Time A-B, RiseIFall A, Events B Dur A, and Width
A).
Noise may be coupled to the input amplifier's along with
the signal to be measured. Noise may originate from the
operating environment, the signal source, or ble caused by
improper connections. If the noise is of sufficient amplitude,
it can result in inaccurate measurements due to false trig-
gering. See Fig. 2-3. The DC 5010 has a 20 MHz low pass
filter (FILTER) that is helpful in removing or reducing noise.
The linear operating range describes the voltage limits
that will allow proper triggering without distortion. The mini-
mum signal amplitudes are defined by the input sensitivity
requirements for the AC COUPL and DC COUF'L modes for
either the 1 MQ or 50 Q Termination selection (see the
Specification section). Proper use of the ATTEN (attenu-
ation) controls will ensure operation within the maximum
limits; t 2.0 V for X I ATTEN, t 10 V for X5 AT'TEN.
Erroneous Count
Triggering1
Level
Shaped
Out
Correct Count
3464-04
Fig. 2-3. Advantages in signal attenuation.