TM 9-4935-282-34
803D
b. ERRORS DUE TO GROUNDING. In the 803D there
is a 0.47 uf capacitor connected from the lower input terminal
(middle post) to chassis ground. If it is desired to make
measurements where the voltage to be connected to the lower
input terminal is not at ground potential, a line cord adapter
must be used to isolate the 803D chassis from line ground.
Otherwise, the 0.47 uf capacitor would place an AC load on the
circuit being measured.
c. INTERNAL CONVERTER NOISE.
When the
instrument is shorted in the AC mode, the converter may
produce a residual noise output of approximately 100 uv. This
noise voltage will cause an insignificant error as long as AC
input signals of 1 mv or larger are applied to the instrument.
the output of the converter amplifier. It is easily seen that the
noise contributes very little to the average value of the signal
and is well within the 2.6% accuracy of the instrument at 1 mv.
d. 0.001 VOLT NULL RANGE - DC ONLY. The 0.001
volt null range is not recommended for use when measuring
Figure 2-7. SIGNAL VOLTAGE WITH CONVERTER NOISE
AC voltages for several reasons. One reason is that most AC
sources are not stable enough. For example, if 0.5 volt is
volt null range for AC is the converter noise discussed in
measured with the range set to 0.5 and the null switch set to
0.001, the effective null detector sensitivity is 100 microvolts
move about erratically on the 0.001 volt null range. Although it
full scale. Since 100 uv is 0.02% of 0.5 volts, an AC source
is difficult to determine how much pointer movement is due to
with a stability worse than 400 parts per million will cause the
converter noise and how much is due to AC source stability,
803D meter pointer to swing from one end of the meter to the
the AC source stability is usually the major source of erratic
other.
Another reason for not using the 0.001
movement.
2-8
