Operating Considerations; Deflection Factors; Input Coupling; Sweep Triggering - Tektronix SC 501 Instruction Manual

OPERATING CONSIDERATIONS
DEFLECTION FACTORS
The amount of vertical deflection produced by a signal is
determined by the signal amplitude, the attenuation factor
(if any) of the probe, the setting of the Volts/Div
pushbuttons, and the setting of the associated VARIABLE
Use the largest deflection factor (1 V/DIV) when first
connecting the SC 501 to an unknown voltage source. If
switch to a lower deflection factor.
The deflection factors indicated by the Volts/Div push-
buttons are calibrated only when the VARIABLE control is
The range of the VARIABLE control is at least 10:1. It
provides uncalibrated deflection factors covering the full
range between the fixed settings of Volts/Div pushbuttons.
The VARIABLE control extends the maximum deflection
factor to at least 10 volts/division.
While most connections to the SC 501 will probably be
made using coaxial cables, probes offer another convenient
method of applying a signal to the input of the SC 501.
Tektronix probes are shielded to prevent pickup of electro-
static interference. A 10X attenuator probe offers a high
input impedance and allows the circuit under test to
perform very close to normal operating conditions. The
SC 501 is compatible with probes such as Tektronix P6006
and P6028 Passive Probes. When probe attenuation is not
desired, a Tektronix P6011 Passive Probe is recommended.
Probe compensation should be checked with a known
signal (risetime of 100 nanoseconds or less) before
using the SC 501. Input time constant is normalized
Unshielded test leads can sometimes be used to connect a
signal source to the SC 501, particularly when a high-level,
low-frequency signal is monitored at a low impedance
point. However, when any of these factors are missing, it
'becomes increasingly important to use shielded cables. In
all cases, the signal transporting leads should be kept as
short as practical. Be certain that a common ground
connection is established between the device under test and
the SC 501. The shield of a coaxial cable or ground strap of
a signal probe provides an adequate common ground
connection.
INPUT COUPLING
The AC COUPL pushbutton switch allows a choice of
input coupling. The type of display desired determines the
method of coupling used.
Dc coupling (button out) can be used for most applica-
tions. However, if the dc component of the applied signal is
much larger than the ac component, ac coupling (button in)
will probably provide a better display. Dc coupling should
be used to display an ac signal below about 3 hertz.
In the ac coupling position, the dc component is blocked
by a series capacitor in the input circuit. The low-frequency
response in the ac position is about 3 hertz (—3 dB point);
therefore, some low-frequency attenuation and phase shift
can be expected near this frequency limit. Distortion will
also appear in square waves that have low-frequency
components.
SWEEP TRIGGERING
When the source switch is in the INT position, the sweep
is triggered by a sample of the signal applied to the VERT
INPUT connector. The display is stable for either Normal
or AUTO triggering modes as long as the signal frequency is
above 10 Hz. Below 10Hz, it may be desirable to use
Normal mode triggering (LEVEL/SLOPE control pushed
in). The AUTO triggering mode (LEVEL/SLOPE control
pulled out) reduces operator adjustments and provides a
When the source switch is in the EXT position, the
sweep is triggered by the signal applied to the EXT TRIG
pin jack. The signal applied to the EXT TRIG pin jack must
be time-related to the signal applied to the VERT INPUT
connector in order to prevent drift in the display.