HP 11049A, Руководство по эксплуатации и обслуживанию, Страница: 9 / 19

Page 3
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RMS INPUT, % OF FULL SCALE
Figure
3.
Input-Output Relationship
9. APPLICATIONS.
10. OUTPUT MEASUREMENTS.
11. The accuracy and sensitivity of thermal converter
measurements are dependent on the accuracy and
resolution of the output measuring circuit. Figure 4
shows a very stahle and sensitive output monitor
circuit. With this circuit, an ou(put change 011.5 flV,
or
O.
01 % of full scale, can easily be resolved. The
Model 11049A
battery powered reference supply generates a stable
reference voltage, opposing the thermal converter
output; and the de null meter monitors the difference
voltage. The battery's short term stability is good
enough thatthe thermal converter output changes may
be read directly
all
the null meter without taking re­
ference voltage drift into consideration. Another stable
and accurate output rneasuring device would be a high
resolution digital voltmeter or differential volhneter.
In order to resolve an input change of 1 % of full scale,
the output monitor should be able to resolve 0. 15 mV;
for an input change of
O.
1% of full scale, it should be
able to resolve 14 flV.
12. To build the reference supply shown in Figure 4 on
the next page, use a mercury battery and wirewound
resistor. The potentiometers should be 10 turn or 20
turn, and the switch should have low thermal contacts.
After constructing the reference supply, place it in a
shielded container and allow the mercury battery toage
in the circuit for about a week. The longer the;battery is
allowed to age ,the better its short term stability will be.
13. All thermal converter measurements should be
made at a constant ambient temperature. Since the
thermoelement responds to the heating effect of the
input, any change in ambient temperature would cause
a slight change in the thermal converter output.
14. FREQUENCY RESPONSE MEASUREMENTS.
15. Figure 4 on the next page shows a test setup for making
simple but accurate frequency response measurements.
The following steps describe the measurement.