HP 11049A, Руководство по эксплуатации и обслуживанию, Страница: 8 / 19

Model 1l049A
4. CALIBRATION.
5. The Hewlett-Packard Standards Laboratory sup­
plies a calibration report on each thermal converter
with a statement of traceability to the National Bureau
of Standards, and also supplies correctional data with
each Option 01 or Option 02 Thermal Converter. The
correctional data is based on the thermal converter!s
comparison with a known reference thermal converter,
and when used with the thermal converters, eliminates
all inaccuracies except the measurement uncertainties
listed in Table 1. If no correctional data is used,
the maximum inaccuracy is the sum of the values
listed in the "with reference to standard" and 1!mea­
surement uncertainty" columns in Table 1.
6.
CIRCUIT DESCRIPTION.
7. The heart of the Thermal Converter is a 90
Q
UHF
thermoelement containing a heater filament and a
thermoelectric junction. The ac current into the
thermoelement heats the filament, and the thermo­
electric junction generates a de voltage proportional
to the filament heat. Therefore, the voltage out of
the thermal converter is proportional to the input
power. Resistor R2 adjusts the current through the
thermoelement to 5 mA with a full scale input, and
Rl adjusts the input impedance to 50
Q.
II049A, i1050A, II051A
THEn MAL CONVERTER
AC
INPUT
�
,
RI
THERMO-
ELEMENT
___
�,�
__ J
"G'�"�b""07Q6
Page 2
0-7MV
DC
OUTPUT
Figure 2. Thermal Converter Schematic Diagram
8. Since the output voltage is a function of input
power, the output varies as the square of the input.
If the input is doubled, the output will be four times
as great; the
if
the input is halved, the output will
drop to one -fourth. For input changes of less
than
3%,
the input-output relationship is essen­
tially linear; and the percent output change is equal
to twice the percent input change. The following for­
mula shows the relationship.
"'Edc
% input change
=
2Edc
X 100
where Edc ::: thermal cOllverter output voltage
Figure
3
shows the input-output relationship.