HP 3478A Technical Manual page 104

3478A
7-F-7 and Figure 7-F-8 for the following simplified ex-
planation of the runup operation.
a. When runup starts, the input voltage (A/D Con-
verter input voltage, not instrument input voltage) is
applied to integrator U401. The resultant input current
(Iin) then charges integrator capacitor C410 and a
certain slope (output of the integrator) is then developed.
This happens at time period TI (see Figure 7-F-8). (The
input voltage is always applied during runup.)
b. After time period T1, a negative going current is
applied to the integrator for a set time period. This cur-
rent, in addition to the input current, charges C410. This
generates a positive going output slope (the integrator
output). The applied current makes sure that the output
slope that follows will cross zero, whether the input
current is positive or negative. The current is applied for
time period T2.
c. After time period T2, the applied current (not the input
current) is removed and a current of opposite polarity is
then applied to U401 for new time period T3 (T3 is twice
as long as T2). The newly applied current is the same
value as the first applied current (at time T2), but at
opposite polarity. The new current then charges Figure
Figure 7-F-8. Integrator (U401) Output Slopes
Figure 7-F-7. Simplified A/D Converter
C410 in the opposite direction (C410 is discharged).
This is because the applied current is larger than the in-
put current.
d.
determines if the output slope crossed zero.
crossing is detected, a current with the same value and
an opposite polarity as the previously applied current is
applied. This current is the same current as the first
applied current and is applied to the integrator for a new
time period T4 (T4 is as long as T3). This current, in
addition to the input current, then charges C410. Since
both currents charge C410, the output slope becomes
steeper and, as shown in Figure 7-F-8, crosses zero.
(because of a larger input voltage), the same current as
the previously applied current is applied for the new time
period T4. The current is reapplied until zero crossing is
detected. (This is shown as the dashed lines in Figure 7-
F-8).
e continues until the runup operation is completed. The
total runup operation lasts for 349 ALE ramps (or
counts).
Controller increments during the positive going slope
periods and decrements during the negative going slope
periods. The counter, in effect, is used to determine the
amount of charge added and subtracted from the input
voltage.
digits of the 3478A's reading is calculated.
7-F-37. Detailed Explanation of Runup. Figure 7-F-9
illustrates the 3478A runup operation in the 4 1/2 digit
mode. Refer to the figure (and Schematic 3) for the
runup explanation in the following steps. The solid lines
(in the figure) showing the runup sequence is for a
7-F-10
When time T3 is completed, the A/D Controller
e. If no zero crossing (in step c) was detected
f. The operation in steps c and d, or in steps c and
g. During the runup operation, a counter in the A/D
From that information, the most significant
TM 11-6625-3071-14
If zero