Tektronix TYPE Z PLIG-IN Instruction Manual page 11

form could be seen but not easily measured.
common-mode rejection of 40,000 to 1, the hum would be
reduced to 0.5 mm and the desired signal alone could be
accurately observed and measured.
The preceding example is shown pictoriaIly in the series
of waveform photographs shown in Figs. 2-4(a), (c), and (d).
A combined 100-volt hum and 0.1-volt square-wave signal
is shown in Fig. 2-4(a). Although the square wave does
not seem to be present, it can be made visible by increasing
the sensitivity of the Z Unit to 0.05 volts/cm, which increases
the effective height of the waveform to 2000 cm. A dc com­
parison voltage (using differential
explained later in this section) of approximately 50 volts
is used to bring the top 4-cm portion of the combined
signals into view, shown by the waveform photograph in
Fig. 2-4(b). The 2-cm high square-wave signal, riding on
top of the hum but not synchronized with it, causes the
separated appearance of the hum signal. Fig. 2-4(c) shows
the 100-volt (p-p) hum signal which, by itself, is applied to
the B input connector. The resulting display using common­
mode rejection is shown in Fig. 2-4(d).
The following five operational notes provide helpful in­
formation to obtain optimum performance from the Z Unit
using this mode of operation.
1. Large-signal response of the Z Unit as a differential am­
plifier is shown in Table 2-1.
TABLE 2-1
Signal Handling Capabilities of the Z Unit
Attenua­ Maximum Minimum
tion Calibrated Uncalibrated
Sensitivity Sensitivity
(volts/cm) (volts/cm)
XI .05 .12
.1 .24
X2
X5 .25 .6
.5 1.2
X10
1 2.4
X20
2.5 6
X50
12
X I 00 5
X200 10 24
25 60
X500
*M axim um continuous dc input level with AC-DC switch set to DC:
volts; momentary maximum dc level should not exceed 1000 volts.
2. Any difference in attenuation factors of the two attenua­
tors (VOLTS/CM switches) will
capabilities of the Z Unit to the extent shown in Table 2-2.
3. Both AC-DC switches should be in the DC position if
possible as explained under
Operation.
4. Differential balance may decrease slightly as the VAR.
ATTEN. control is adjusted
(clockwise) position.
@2
With a
comparator operation
Maximum
Magni­
Signal or fication
Common Factor
Mode
(volts)
100 2000X
200 1000X
500 400X
1000* 200X
1000* 100X
1000* 40X
20X
1000*
10X
1000*
5X
1000*
800
decrease the differential
Conventional Preamplifier
aw ay from the calibrated
Operating Instructions — Type Z
5. Either input signal alone may be viewed without switch­
ing back to the A O N LY or — B O N LY positions of the
Mode switch by depressing the PUSH TO DISCONNECT
SIGN AL button of the other input channel.
TABLE 2-2
Typical Attenuator Performance
Attenuator Attenuator
Accuracy, ± %
0
XI
X2 1
X5 1.5
X10 and up 2
If a conventional probe is used, the probe resistor tolerance of 2 %
creases the Z Unit attenuator accuracy.
curately measured as explained later under Attenuator Test Point.
Calibrated Differential Comparator Operation
When the Mode switch is in the A-Vc or Vc-B position,
the Z Unit is a calibrated differential comparator or slide-
back voltmeter. The calibrated comparison voltage, which
has a range of 0 to 100 volts, may be added (differentially)
to either input signal.
In this mode a calibrated dc voltage is internally applied
to cancel out any unwanted dc component in the applied
signal, thereby allowing accurate measurements of relative­
ly small ac signals riding on top of relatively large dc
signals.
When the Mode switch is in the A-Vc position, the com­
parison voltage is applied internally to the amplifier input
where the B signal is ordinarily applied during differential
mode of operation. The switches and input connector in
the —B O NLY section of the front panel are not used.
Signals applied to the B input connector will not be ob­
served.
In Vc-B position of the Mode switch, the comparison
voltage is applied to the amplifier input where the A input
signal is normally applied during differential mode of op­
eration. All switches and the input connector in the A O NLY
section of the front panel are not used.
The dc comparison voltage is set by 3 controls: the COM ­
PARISON VO LTAG E Polarity, Range, and Helidial.
Range control has ranges of 0 to 1, 0 to 10, and 0 to 100
volts. The Helidial varies the comparison voltages over
this range and indicates the precise comparison voltage at
any particular setting.
NOTE
The regulator circuit in the Z Unit m aintains con­
stant, accurate, comparison voltages as long as
the oscilloscope — 150-
supplies are in regulation and within their output
voltage tolerance ratings. Be sure these and other
regulated power supplies in the oscilloscope are
operating properly.
Differential comparator mode of operation may be used
to make the following voltage measurements: (1) dc volt­
age measurements, (2) ac signal measurements superimposed
on dc, and (3) high-amplitude ac signal measurements.
Input Resistance
Tolerance, ± %
1
1
1
1
de­
These inaccuracies can be ac­
The
and + 225-volt power
2-5