Tektronix TYPE Z PLIG-IN, Инструкция по эксплуатации

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Operating Instructions — Type Z
Checking Attenuation Accuracy of VOLTS/CM
Switches
The attenuation accuracy of the X2, X5, X I 0, and X20
positions of the VOLTS/CM switches can be determined by
utilizing the 100-volt comparison voltage available at the
ATTEN TEST PT connector. The following procedure ex­
plains how to check the X2 position of the A VOLTS/CM
switch. The other positions are checked in the same manner.
1. Set the A VO LTS/CM switch to X2, the AC-DC switch to
DC, and the Mode switch to A-Vc.
2. Place the COM PARISON VO LTA G E Polarity switch to 0
and position a free-running trace to the center of the screen
for reference.
3. Remove the left side panel from the oscilloscope. Connect
a test lead from the A input connector to the ATTEN TEST
PT connector (see Fig. 2-6).
Fig. 2-6. Left side view of the Z Unit showing the location of the
ATTEN TEST PT.
C A U T IO N
Use care in m aking the test lead connections to
prevent shorting the 100 volts a t the ATTEN TEST
PT to ground.
An accid e n tal short circuit m ay
d am age the C A L. 4 adjustm ent (R 7 6 8 4 ).
4. Set the COM PARISON V O LTA G E Polarity switch to +
and the Range switch to 100 V.
5. Rotate the Helidial to return the trace to the reference
level obtained in step 2. Use the vertical trace indicator
lights to aid in returning the trace. In this example the
Helidial should end up in the vicinity of 5.00 (or 50 volts).
divider resistor R1 is the 1-meg input resistor in the oscil­
loscope, R2 is the resistor in the probe. The procedure which
follows describes a method for checking a 10X attenuator
probe.
1. Set the A VOLTS/CM switch to X I, the AC-DC switch to
DC, and the Mode switch to A-Vc.
2. Place the COMPARISON VO LTAG E Polarity switch to 0
and position a free-running trace to the center of the screen
for reference.
3. Remove the left side panel from the oscilloscope (if not
already removed). Connect the probe cable connector to
the A input connector on the Z Unit and connect the probe
tip to the ATTEN TEST PT.
4. Set the COMPARISON V O LTAG E Polarity switch to +
and the Range switch to 100 V.
5. Rotate the Helidial to return the trace to the reference
level obtained in step 2. In this example the Helidial should
end up near a reading of 10 volts.
6. Divide the Helidial reading into 100 to obtain the at­
tenuation factor of the probe.
Checking External Resistors
External resistors can be checked for value against the
1-megohm input resistance of the unit by using the bridge
circuit of Fig. 2-5. In this application, R2 is the resistance
to be measured and R1 is the internal 1-megohm resistor.
The following procedure can be used:
1. Set the A VOLTS/CM switch to X I, the AC-DC switch to
DC, and the Mode switch to A-Vc.
2. Place the COMPARISON VO LTAG E switches to 0 and
100 V. Position a free-running trace to the center of the
screen for reference.
3. Remove the left side panel of the oscilloscope. Connect
one end of R2 to the A input connector and the other end
to the ATTEN TEST PT (see Fig. 2-6) by using a jumper
wire.
4. Set the COMPARISON V O LTAG E Polarity switch to + .
5. Adjust the Helidial to return the trace to the reference
level obtained in step 2.
Use the vertical trace indicator
lights to aid you in returning the trace.
6. Let H be the Helidial reading. Then use the folowing
equation to find the value of R2.
R2 = R1
10 - H
H
10 - H
H
Megohms.
6. Divide the Helidial reading into 10 to obtain the at­
tenuation factor. (Assume the Helidial reading to be 5.02.
5.02 divided into 10 is 1.99 or an attenuation factor of XI .99.
The attenuation ratio is 1.99 to 1).
Checking Attenuation Accuracy of Probes
Passive attenuator probes can be checked for attenuation
accuracy by a method similar to that used for determining
the VO LTS/CM attenuation accuracy. Referring to Fig. 2-5,
If R2 is small compared to 1 megohm, the Helidial read­
ing will be very close to 10.00 making it difficult to obtain
an accurate measurement. When this occurs, R1 can be
shunted by an accurate external resistor which will permit
Helidial readings around 5.00. The only restriction on the
shunting is that the total resistance to ground from the
ATTEN TEST PT should not be less than 20 k. This limits the
current drawn from the test point to a maximum of 5 ma. If
the 1-megohm resistor is shunted, R1 in the equation will
have to be changed to the new value of the 1-megohm
and shunt resistors in parallel.
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