I
P6021
WARNING
THE FOLLOWING SERVICING INSTRUCTIONS
ARE FOR USE BYQUALIFIED PERSONNEL ONLY.
TO AVOID PERSONAL INJURY, DO NOT
PERFORM ANY SERVICING OTHER THAN THAT
CONTAINED IN OPERATING INSTRUCTIONS
UNLESS YOU ARE QUALIFIED TO DO SO.
SECTION
3
CIRCUIT DESCRIPTION
Introduction
This section of the manual contains descriptions of the
circuitry in the P6021 Current Probe and Termination. Com·
plete circuit schematics are given in the Diagrams section.
Ref'er to these diagrams throughout the following circuit
descri ption.
Current Probe
The P6021 Current Probe consists of
0
current transformer
mounted in the nose of the case, an impedance matching
network, and a switch to disconnect the transformer shield
from ground.
The transformer contains a two-section U-shoped ferrite
core. One section is stationary, the other is mechanically
movable to permit closing the core around the conductor
being measured. The conductor under test forms a one·turn
primary winding for the transformer; the windings around
the stationary portion of the core form the secondary wind
ings. Paralled windings in the secondary assure a fast step
response. The circuitry between the transformer and the
coaxial cable corrects any difference in level between the
pulses induced in the paralled windings of the secondary,
and matches the balanced probe winding to the cable.
3-1
As indicated on the probe body, the turns ratio of the
P6021 Curent Probe is 125:1 . This refers to the number of
windings in the secondary of the probe transformer. The
two turns ratios manufactured by Tektronix, Inc. are 50,1
and 125,1 . Due to the comparatively high inductance in
the secondary of the 1 25:1 probe, the P6021 operates at a
lower frequency range than the 50; 1 probe.
The probe transformer is shielded to eliminate interference
from outside signals. To eliminate the possibility of shorting
this shield to the conductor being measured when connecting
or removing the probe, slide switch SW20 disconnects the
ground from the shield when the slide portion of the probe
is open.
Termination
The P602 1 Termination consists of a 62.5-ohm impedance
matching network to terminate the coaxial cable, and a
voltage divider which is switched in by a slide switch,
changing the sensitivity by a factor of five. With the slide
switch in the 2 mA/mV position, a ten milliampere current
signal in the conductor under test induces a five millivolt
signal at the output of the termination, when the termination
is connected to a one-megohm input oscilloscope. In the
10 mA/mV position, the signal is attenuated to produce a
one millivolt signal at the output.
REV
B JUN 1980
