Tektronix 2221A - Displaying Signals; Precharging the Signal Input

Displaying signals
signal loading in the circuitry under test. The connector ends of the accesso
ry 10X probes are coded to change the readout by the appropriate scale
factor.
□ Step 1 : Gently twist the probe connector clockwise onto the input BNC
until it locks.
□ Step 2: Make sure the probe is properly compensated. Refer to Check
ing the Probe Compensation, page 1-6.
f~l Step 3: Connect the ground clip on the probe to the ground connection
of the circuit. This will reduce signal noise and provide a common
ground reference for DC measurements.
Probe Accessories — Tektronix also supplies many other types of probes
and probe accessories to meet your measurement needs. Your Tektronix
representative, local Tektronix Field Office, or Tektronix products catalog can
also provide additional information on accessories.
Coaxial Cables — Use a coaxial cable to connect a BNC output or other
terminated signal source to the oscilloscope input. If necessary, use a
termination (usually 50 Q) on the signal input to match the characteristic
impedance and preserve the fidelity of the signal. Tektronix also carries a
variety of coaxial cable and cabling accessories for various applications.
Coupling Signals
Use the AC-GND-DC switch to select the desired input coupling mode
(Figure 3-1).
AC — Capacitively couples the input and blocks DC to 10 Hz signals.
GND — Decouples the signal from the input and connects the input circuit
to ground reference.
DC — Passes all signal components (AC and DC) to the vertical system.
Precharging the Signal Input
Use the procedure below when coupling AC signals that have a high DC
voltage level or when probing between signals that differ greatly in DC
levels. This procedure becomes especially useful if the difference in DC level
is more than ten times the volts/division switch setting or if the circuit is
sensitive to the charging, or discharging, of the internal AC coupling capaci
tor.
n Step 1: Set the input coupling switch to GND before connecting the
probe tip to a signal source.
I~~1 Step 2: Touch the probe tip to the oscilloscope chassis ground (GND)
connector.
□ Step 3: Wait several seconds for the input-coupling capacitor to dis
charge.
3-2
In Detail