HP 11049A, Руководство по эксплуатации и обслуживанию, Страница: 10 / 19

Model l1049A
DO NOT EXCEED THE RATED INPUT OF
THE THERMAL CONVERTER.
ALWAYS
REDUCE THE INPUT BEFORE CHANGING
FREQUENCY RANGE OF CIRCUIT UNDER
TEST. ANY OVERLOAD OR HIGH VOLT­
AGE TRANSIENT MAY DESTROY THE
THERMO ELEMENT.
OSCILLATOR
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NULlMETER
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THERMAL CONVERTER
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Figure 4. Frequency Response Measurements
a. Set oscillator and reference supply output
levels to minimum.
b. Connect null meter, reference supply, and
thermal converter as shown in Figure 4.
Keep cables connecting oscillator and thennal
converter as short as possible.
Page 4
c. Adjust oscillator amplitucle for a null meter
indication of about
7
mY.
d. Adjust reference supply for null indication
within 1 MV. Once null is obtained, do not
readjust oscillator amplitude or reference
supply output.
e. Change frequency and note thermal converter
output changes. Remember that percent con­
verter output change equals twice percent in­
put signal change.
16. GENER.t,.TlNG AN ACCURATE CALIBRATION
SIGNAL.
17.
The test setup in Figure 5 on the next page generates
a test signal that may be used for both frequency response
and absolute value calibration at any frequency within the
thermal converter range. A dc standard acts as the
absolute value reference, and a stable test oscillator
generates the calibration signal. With 81 set to the
DC position and the de standard output set to the de­
sired calibration voltage, the reference supply is
adjusted for a null indication on the null meter. Then
Sl is SWitched to AC, and the oscillator output is
adjusted to reestablish a null indication. This sets
the rms value of the oscillator output equal to the de
standard output. The oscillator output goes to the
instrument under test,
18. DC REVERSAL ERROR.
19, DC inputs of opposite polarity will produce slightly
different outputs from the thermal converter, and the