Tektronix TYPE Z PLIG-IN Instruction Manual page 12

Operating Instructions — Type Z
1. DC Voltage Measurements.
When the Z Unit is used to make any dc voltage measure­
ments, it is first necessary to establish a reference line on
the screen of the oscilloscope. This line will usually be the
horizontal centerline of the graticule.
reference, set the COMPARISON VO LTAG E Polarity switch
to 0 and press the appropriate PUSH TO DISCONNECT
SIGN AL button to disconnect the input signal.
previously under Conventional Preamplifier Operation, slight
trace deviation from exact zero must be taken into account
to obtain best accuracy.)
set the oscilloscope trace at the centerline of the graticule.
To measure a dc voltage component of ± 1 0 0 volts or less,
apply the input signal to one of the connectors.
ample, suppose the signal
connector, then proceed as follows:
(a) Place the A VOLTS/CM switch to .05 and the Mode
switch to the A-Vc position.
(b) If the dc voltage component to be measured is posi­
tive, place the COMPARISON VO LTAG E Polarity switch to
the + position. If it is between 10 and 100 volts, set the
COMPARISON VO LTAG E Range switch to 100 V.
(c) Rotate the COMPARISON VO LTAG E Helidial to bring
the desired portion of the trace onto the screen. Set the
trace exactly on the reference line with the Helidial.
(d) Recheck the reference as described in the first para­
graph.
(e) When the zero reference line and signal trace appear
at the same place on the screen, the input voltage and
the comparison voltage are equal.
2. A C Signal Measurements Superimposed on DC
Small ac signals superimposed on a dc component can
be measured accurately by first using the comparison volt­
age to effectively eliminate the dc component.
signal can then be measured in the same manner as in con­
ventional preamplifier operation. The VAR. ATTEN. control
must be kept clockwise to obtain correct results.
3. High-Amplitude AC Signal Measurements.
High-amplitude ac signals, subject to the rise rate and fall
rate limitations listed in the Specifications section, can also
be measured with the Z Unit at maximum sensitivity. This
type of measurement is very similar to dc measurements
except that it is not necessary to establish a zero voltage
reference line unless measurements of both ac and dc volt­
age levels are to be made. To measure the voltage differ­
ence between two points on the waveform, proceed as fol­
lows:
(a) Set the Helidial to zero and position one point on the
waveform to the horizontal centerline of the graticule.
(b) Use the Helidial and Range controls to bring the other
desired point to the centerline.
2-6
To establish the
(As noted
Use the POSITION control to
For ex­
is applied to the A input
The ac
(c) The voltage difference between the two points is
read from the Helidial and the setting of the Range switch.
AC-DC Voltage Measurements Exceeding ±100
Volts.
If ac, dc, or both ac and dc voltage components are
greater than ± 1 0 0 volts, the .05 settings of the VOLTS/CM
switches cannot be used. It will be necessary to use a lower
sensitivity in order to prevent overdriving the preamplifier
and to prevent exceeding the comparison voltage available.
To obtain the correct voltage measurement, use the multi­
plication factor which appears below the volts per centi­
meter setting on the VOLTS/CM knob. The product of the
multiplication factor times the comparison voltage used
is the input signal voltage.
ATTENUATOR TEST POINT
Two applications included here show how the ATTEN
TEST PT connector, located on the left side of the Z Unit,
can be used to make attenuation factor or ratio checks on
probes used with the Z Unit and on the internal attenuators
of the unit. The test point, when connected to a voltage
divider network under test, forms a bridge circuit as shown
in Fig. 2-5. The crt is the null indicator and the Helidial
reading is used to determine the attenuation factor or ratio
of the divider resistors.
A third application describes how the unit may be used
to measure external resistors.
+ 100 V
Fig. 2-5. Simplified diagram of the bridge circuit formed during
use of the ATTEN TEST PT connector.