Basic Operation; General Operating Information - Tektronix 7a15a Instruction Manual

Operating Instructions-7A15A/7A15AN
General . This procedure demonstrates the use of the
connectors and controls of the 7A15A/7A15AN, while at
the same time providing a means of checking the basic
operation of the instrument .
Preliminary Setup. Install the 7A15A/7A15AN into any
7000-series oscilloscope vertical compartment and set the
oscilloscope VERTICAL MODE and TRIGGER SOURCE
to the proper settings .
Install a 7-series time-base unit into a horizontal
compartment and set the oscilloscope HORIZONTAL
MODE to the proper setting. Set the time-base unit to a
sweep rate of one-millisecond per division and set the
triggering mode to AUTO .
Procedure
1 . Set the 7A15A/7A15AN AC-GND-DC switch to
GND and position the trace to the center of the graticule.
2 . Set the VOLTS/DIV switch to 10 mV and apply a 40
mV 1 kHz square-wave signal from the oscilloscope CALI-
BRATOR to the 7A15A/7A15AN INPUT connector. Set
the AC-GND-DC switch to DC and check for a four-division
display .
3. Set POLARITY switch to INVERT and check that
the displayed signal is inverted as compared to its appear-
ance in step 2.
4. Set the AC-GND-DC switch to AC and check that the
trace is centered on the CRT graticule.
5. Set the oscilloscope CALIBRATOR to 4 mV and the
7A15A/7A15AN MAG switch to X10 . Check for a four-
division display.
6. (7A15A Only) Press the 7A15A IDENTIFY button,
check that the display moves upward approximately 0.3
division and the readout (if so equipped) reads
"IDENTIFY" .
GENERAL OPERATING INFORMATION
Signal Connections
BASIC OPERATION
In general, probes offer the most convenient means of
connecting a signal to the input of the 7A15A/7A15AN . A
10X attenuator probe offers a high impedance and allows
2-2
the circuit under test to perform very close to normal
operating conditions .
The Tektronix P6053 probe is equipped with a readout
coding ring which connects to a circuit in the amplifier
unit . This automatically corrects the readout displayed on
the CRT to the actual deflection factor at the tip of the
probe. This probe is recommended for use with the 7A15A
and an oscilloscope equipped with readout. The Tektronix
P6054 probe is electrically identical to the P6053 but is
intended for use with systems not equipped with readout.
For more information refer to the Tektronix Inc. catalog .
Vertical Gain Check and Adjustment
To check the gain of the 7A15A/7A15AN, set the
VOLTS/D IV switch to 10 mV and connect a 40 mV, 1 kHz
signal from the oscilloscope calibrator to the Input connec-
tor. The vertical deflection should be exactly four divisions .
If not, adjust the front panel GAIN for exactly four divi-
sions.
Input Coupling
The AC-GND-DC switch allows a choice of input coup-
ling methods. The type of display desired and the applied
signal will determine the coupling to use.
The DC coupling position can be used for most applica-
tions. For AC signals with frequencies below about 30 Hz
(10 Hz with a 10X probe), and square waves whose low-
frequency components are important to the display, it is
necessary to use DC coupling to obtain a satisfactory
presentation .
In the AC coupling position the DC component of the
signal is blocked by a capacitor in the input circuit. The AC
coupling position provides the best display of signals with a
DC component much larger than the AC component. The
pre-charge feature should be used when there is a possibility
of having a residual charge on the input capacitor of the
opposite polarity to the intended input, and when the
algebraic sum of the combination of charges may be greater
than the maximum input limitations of the amplifier . To
use this feature, first set the coupling switch to GND, then
connect the probe to the circuit and wait about two
seconds for the coupling capacitor to charge, set the
coupling switch to AC .
The GND position provides a ground reference at the
input of the amplifier without externally grounding the
Input connectors . However, the signals connected to the
inputs are not grounded, and the same DC load is presented
to the signal source .