HP 3478A Technical Manual page 104

3478A 3478A
7-F-7 and Figure 7- 7-F-7 an d Figure 7-F-8 for the following simplified ex- F-8 for the following simplified ex-
planation of the runup operation. planation of the runup operation.
a. a. When ru When runup s nup star tarts, t
verter input voltage, not instrument input voltage) is verter input voltage, not instrument input voltage) is
applied to integrator applied to integrator U401. U401. The resultant
(Iin) then charges integrator capacitor C410 and a (Iin) then charges integrator capacitor C410 and a
certain slope (output of the integrator) is then developed. certain slope (output of the integrator) is then developed.
This happens at time period TI (see This happens at time period TI (see Figure 7-F-8).
input voltage is al input voltage is always applied during runup.) ways applied during runup.)
b. b. Afte After ti r time pe me period riod T1,
applied to the applied to the integrator for integrator for a set time period
rent, in addition rent, in addition to the input cur to the input current, charges C410
generates a positive going output slope (the integrator generates a positive going output slope (the integrator
output). The applied curren output). The applied current makes sure that t
slope that follows will cross zero, whether the input slope that follows will cross zero, whether the input
current is positiv current is positive or negativ e or negative. e. The current is applied for
time period T2. time period T2.
c. c. After time period T2, the applied curr After time period T2, the applied current (not the input
current) is removed and a current of opposite polarity is current) is removed and a current of opposite polarity is
then applied to U401 for new time period T3 (T3 is twice then applied to U401 for new time period T3 (T3 is twice
as long as T2). as long as T2). The newly The newly applied current
value as the first applied current (at time T2), but at value as the first applied current (at time T2), but at
opposite polarity. opposite polarity. The new curr The new current then cha
Figure 7-F-8. Figure 7-F-8. Integrator Integrator (U401) Output
Figure 7-F-7. Simplified A/D Figure 7-F-7.
ts, the in he input v put volt oltage ( age (A/D Co A/D Con- n-
The resultant input current input current
Figure 7-F-8). (The
T1, a neg a negativ ative goi e going cu ng current
a set time period. . This cur- This cur-
rent, charges C410. . This
t makes sure that the output he output
The current is applied for
ent (not the input
applied current is the same is the same
ent then charges rges Figure
(U401) Output Slopes Slopes
Simplified A/D Converter Converter
C410 in the opposite direction (C410 is discharged). C410 in the opposite direction (C410 is discharged).
This is because the applied current is larger than the in- This is because the applied current is larger than the in-
put current. put current.
d. d. When time When time T3 is
determines if the out determines if
crossing is detected, a current with the same value and crossing is detected, a current with the same value and
an opposite polarity as the previously applied current is an opposite polarity as the previously applied current is
(The applied. applied. This current
applied current and is applied to the integrator for a new applied current and is applied to the integrator for a new
rrent is is time period T4 (T4 is as time period
addition to the input addition to
This both currents charge C410, the output slope becomes both currents charge C410, the output slope becomes
steeper and, as shown in Figure 7-F-8, steeper and, as shown in
e. e. If n
(because of a larger input voltage), the same current as (because of a larger input voltage), the same current as
the previously applied current is applied for the new time the previously applied current is applied for the new time
period T4. The current period T4.
detected. (This is shown as the detected.
F-8). F-8).
f. f.
e continues until the run e continues u
total runup operation lasts for 349 ALE ramps (or total runup operation lasts for 349 ALE ramps (or
Figure counts). counts).
g. g. Durin
Controller increments during the positive going slope Controller increments during the positive going slope
periods and decrements during the negative going slope periods and decrements during the negative going slope
periods. The counter, in periods.
amount of charge added and subtracted from the input amount of charge added and subtracted from the input
voltage. voltage.
digits of the 3478A's reading is calculated. digits of the 3478A's reading is calculated.
7-F-37. Detailed E 7-F-37.
illustrates the 3478A runup operation in the 4 1/2 digit illustrates the 3478A runup operation in the 4 1/2 digit
mode. mode.
runup explanation in the runup explanat
(in the figure) showing the runup sequence is for a (in the figure) showing the runup sequence is for a
7-F-10 7-F-10
T3 is completed, completed, the A/
the output slope put slope crossed zero
This current is the is the same current same current as the
T4 (T4 is as long as T3). long as T3). This current,
the input current, th current, then charges C41 en charges C410. 0. Since
Figure 7-F-8, crosses zero.
If no ze o zero cr ro cross ossing ( ing (in st in step c) w
The current is reapplied until is reapplied until zero crossing is
(This is shown as the dashed lines in Figure 7-
The ope The operation ration in st in steps c eps c and d
ntil the runup operation is complet up operation is completed.
During th g the ru e runup nup opera operation,
The counter, in effect, is used to det effect, is used to determine the
From t From that hat information, information, the
Detailed Explanation xplanation of of Runup.
Refer to Refer to the figure the figure (and Schematic (and Schematic 3) for
ion in the following steps. following steps. The solid lines
TM 11-6625-3071-14 TM 11-6625-3071-14
the A/D Cont D Controller roller
crossed zero. . If zer If zero o
as the first first
This current, in in
Since
crosses zero.
ep c) was de as detec tected ted
zero crossing is
dashed lines in Figure 7-
and d, or , or in steps in steps c and c and
ed. The The
tion, a cou a counter nter in th in the A/ e A/D D
ermine the
the most most significant significant
Runup. Figure 7-F-9 Figure 7-F-9
3) for the the
The solid lines