Tektronix 5A14N Instruction Manual page 7

Operating lnstructions~5A141\l
close to normal operating conditions. The 5A14N is
designed for compatibility with coded probes, such as the
Tektronix P6060 and P6052 Passive Probes. The input
connector has an outer ring to which the coding ring on the
probe connector makes contact. This type of probe allows
the vertical deflection factor indicated by the readout to
correspond with the actual deflection factor at the probe
tip, eliminating the need to consider the attenuation factor
of the probe when measuring the signal amplitude on the
graticule scale. See your Tektronix, Inc., catalog for
characteristics and compatibility of probes for use with this
system.
Sometimes unshielded test leads can be used to connect
the 5A14N to a signal source, particularly when a high-
level, low-frequency signal is monitored at a low-impedance
point. However, when any of these factors is missing, it
becomes Increasingly important to use shielded signal
cables. In all cases, the signal transporting leads should be
kept as short as practical. Be sure to establish a common
ground connection between the device under test and the
5A14N. The shield of a coaxial cable or ground strap of a
signal probe provides an adequate common ground connec¬
tion.
Channel Sequence Logic
The 5A14N has two channel-sequence modes selected
by the internal Single Beam/Dual Beam selector. In the
forward or Single Beam position (toward the front panel),
the channels are displayed in a 4-3, 4-3, 2-1, 2-1 sequence.
In the rear or Dual Beam position, the channels are dis¬
played in a 4-3-2-1, 4-3-2-1 sequence. The Single Beam
sequence is necessary in order to display all channels when
operating with a single-beam 5100-Series Oscilloscope
where each vertical compartment is given two time slots in
sequence before the other compartment receives its two
time slots. Since a possible four channels per compartment
may be desired, a double count of each 4-3 and 2-1 pair is
necessary. The Dual Beam sequence is useful when only one
vertical compartment of a single-beam oscilloscope is being
used, or when a dual-beam oscilloscope is being used in any
YT mode.
Input Coupling
The AC-DC pushbutton switch allows a choice of input
coupling. The type of display desired will determine the
coupling used.
DC coupling {button out) can be used for most
applications. However, if the DC component of the 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 AC signals below about 2 hertz as
they will be attenuated in the AC position.
In the AC position, the DC component is blocked by a
capacitor in the input circuit. The low-frequency response
in the AC position is about 2 hertz (--3 dB point).
Therefore, some low-frequency attenuation can be
expected near this frequency limit. Distortion will also
appear in square waves which have low-frequency
components.
The GND pushbutton provides a ground reference at the
amplifier input. The signal applied to the input connector is
presented with a one-megohm load, while the amplifier
input is grounded. This eliminates the need to externally
ground the input to establish a DC ground reference.
Pre-charging. To minimize surge currents in the circuit
under test when using deflection factors of 50 mV/Div
through 1 mV/Div and a test lead or IX probe, use the
AC-DC and GND pushbuttons to take advantage of the
pre-charging circuit incorporated in the unit. The pre¬
charging circuit permits charging the coupling capacitor to
the DC source voltage when the AC and GND buttons are
pressed in, and also limits surge current to the coupling
capacitor from the signal source. The procedure for using
this circuit is as follows:
a. Before connecting the 5A14N to a signal containing a
DC component, push in the AC and GND buttons. Then
connect the input to the circuit under test.
b. Wait about one second for the coupling capacitor to
charge.
c. Remove the ground from the coupling capacitor
{GND button out). The display will remain on-screen and
the AC component can be measured in the usual manner.
Deflection Factor
The amount of trace 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
switch, and the setting of the Variable control. The
deflection factors indicated by the VOLTS/DIV switch are
calibrated only when the CAL control Is rotated fully
clockwise into the detent position.
The range of the CAL control is at least 2.5:1. It
provides uncafibrated deflection factors covering the full
range between the fixed settings of the VOLTS/DIV switch.
The control can be set to extend the deflection factor to at
least 12.5 volts/division.
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