HP 3478A Technical Manual page 108

3478A 3478A
b. b. If it h If it has be as been de en deter
voltage on the integrator is negative, S-4 currents are voltage on the integrator is negative, S-4 currents are
applied a number of times until zero crossing occurs applied a number of times until zero crossing occurs
(CMP output (CMP output changes state). changes state). Since the S-4 curren
be applied (during time TI in Figure 7-F-14) be applied (during time TI in
maximum of three ramps, the resultant output slope S-4 maximum of three ramps, the resultant output slope S-4
will normally cross zero with three or less S-4 currents will normally cross zero with three or less S-4 currents
applied. applied. After zero After zero crossing crossing occurs,
removed with 15 ALE removed with 15 ALE cycles (i.e.
the S-4 the S-4 slope crosses slope crosses zero.
removed) time TI is not completed, a no current removed) time TI is not completed, a no current
condition remains (i.e. an S-O slope) for condition remains (i.e.
TI. TI. No current is applied No current is applied to keep
constant. constant.
c. c. If t If the re he remai mainin ning vol
positive, current S-4 is applied for a short time and then positive, current S-4 is applied for a short time and then
removed. removed. The The current current is applied
because the current develops a positive output slope and because the current develops a positive output slope and
the integrator the integrator voltage is also positiv voltage is also positive. e. Both the slope and
the integrator voltage together could saturate the the integrator voltage together could saturate the
integrator. integrator. When Current S-4 is r When Current S-4 is removed, no current
S-0 slope) S-0 slope) is then ap is then applied for the plied for the rest of time
rent S-4 is applied whether the integrator voltage is rent S-4 is applied whether the integrator voltage is
positive or negat positive or negative. ive. This is to make sure that t This is to make sure that the slopes
that follow (slope S + 4) will always cross zero and that that follow (slope S + 4) will always cross zero and that
the same transitions occurs for all readings. the same transitions occurs for all readings.
d. d. The n The next ext cur curren rent ap
current. Its value is current. Its value is the same as S-4, b the same as S-4, but in the opposite
direction. The current is direction. The current is applied until
zero. The current zero. The current can be can be applied (durin
maximum of three maximum of three ramps. ramps. This makes time T2 t
as time TI. as time TI. The S+4 currents are The S+4 currents are also removed within
ALE cy ALE cycles after cles after the S+4 the S+4 slope crosses
again, no current is applied (slope S-0) for the re- again, no current is applied (slope S-0) for the re-
mainder of time T2. mainder of time T2.
e. e. Aft After t er time T ime T2, t 2, the ne
negative S-3 current (its polarity is opposite of S + 4). negative S-3 current (its polarity is opposite of S + 4).
Because the value of an S-3 current is 1/10 the value of Because the value of an S-3 current is 1/10 the value of
an S-4 cur- rent, the resultant S-3 slope is not as steep an S-4 cur- rent, the resultant S-3 slope is not as steep
and takes and takes longer time longer time to cross
maximum number of times the currents can be applied maximum number of times the currents can be applied
(during time T3) seven (during time T3) seven times instead
current is also removed within 15 ALE cycles after slope current is also removed within 15 ALE cycles after slope
S-3 crosses z S-3 crosses zero. ero. Then no curr Then no current (S-0)
the re- mainder of time T3. the re- mainder of time T3.
f. f. When tim When time T3 e T3 is c is comp
2 is applied. 2 is applied. This current is 1/10 the v This current is 1/10 the value of S-3 (1/100
of S-4) and in of S-4) and in the o the opposite d pposite direction.
number of times the S + 2 current can be applied is number of times the S + 2 current can be applied is
seven (as seven (as are S-3 are S-3 currents). currents). Time T4 has
amount of time as T3. amount of time as T3. The S +
removed within 15 ALE cycles after slope S+2 crosses removed within 15 ALE cycles after slope S+2 crosses
zero. zero. Then no current ( Then no current (S-0) is applied for t
of time T4. of time T4.
g. g. The The nex next c t curr urrent ent app
cur- rent is 1/10 the value of S+2 (1/1000 of S+4) and in cur- rent is 1/10 the value of S+2 (1/1000 of S+4) and in
the opposite direction. the opposite dir ection. The current The current is applied until
termin mined th ed that th at the rema e remaini
Since the S-4 currents can
Figure 7-F-14) to to a a
occurs, the the current current is is
cycles (i.e. one half-ramp) aft one half-ramp) after er
zero. If (after If (after the curren the current is
an S-O slope) for the rest of time the rest of time
to keep the r the rundown time undown time
g voltag tage on th e on the int e integr egrato
is applied for a for a short short time
Both the slope and
emoved, no current (an
rest of time T1.
t appli plied is p ed is posi ositiv tive S + 4 e S + 4
ut in the opposite
applied until slope S+4 cro slope S+4 crosses
applied (during time T2) g time T2) a a
This makes time T2 the same
also removed within 15
slope crosses zero. zero.
he next cu xt curre rrent a nt appl
to cross zero. zero. This makes the This makes the
times instead of three. of three. The S-3
ent (S-0) is applied is applied for
omplet leted, ed, pos positi itive c ve curr urrent
alue of S-3 (1/100
irection. The maximum The maximum
Time T4 has the same
The S + 2 currents ar 2 currents are also
S-0) is applied for the remainder he remainder
applie lied i d is n s nega egativ tive S e S-1.
is applied until it it
ining ng
crosses zero crosses zero. . The currents are
ALE cycles after slope S-I crosses zero. ALE cycles after slope S-I crosses zero.
h. h. Onc
ts can + I current is applied for 5 ALE cycles and is called one + I current is applied for 5 ALE cycles and is called one
sixth ramp. This current is sixth ramp.
and only and only happens
the same value as S-l, but the same va
currents are applied until zero crossing occurs and are currents are applied until zero crossing occurs and are
removed within 5 ALE cycles after crossing zero. removed within 5 ALE cycles after crossing zero.
t is i. i.
cycles, current S-I cycles, cur
also applied until ze also applied
cross zero, current S + 1 is reapplied. cross zero, current
is removed, S-I is applied is removed,
ator is r is until time T5 (and rundown) is completed. until time T5 (and rundown) is completed.
j. j.
time Controller counts the number of S-4, S + 4, S-3, S + 2, Controller counts the number of S-4, S + 4, S-3, S + 2,
and S-1 slopes it takes for each set of slopes to cross and S-1 slopes it takes for each set of slopes to cross
zero. zero.
significant digits of the 3478A's reading. significant digits of the 3478A's reading.
(an
7-F-46. 7-F-46.
T1. Cur- Cur-
Integrator can have offsets which prevent the S + 2 and Integrator can have offsets which prevent the S + 2 and
S- 1 slopes from S- 1
he slopes
slopes will cross zero, the A/D's DAC (Digital to Analog slopes will cross zero, the A/D's DAC (Digital to Analog
Con- verter, U465 and associated circuitry) is turned on Con- verter, U465 and associated circuitry) is turned on
before the S + 2 currents are before the S
to null out any offsets from t to null out a
number of times the S + 2 current can be applied is number of times the S + 2 current can be applied is
sses
seven (as seven (as are S-3
amount of time as amount of
he same
removed within 15 ALE cycles after slope S + 2 crosses removed within 15 ALE cycles after slope S + 2 crosses
15
zero. Then no current (S-0) zero.
Here Here
of time T4. of time T4.
7-F-47. The correct 7-F-47.
the time when the S+ I and S-I currents are applied. the time when the S+ I and S-I currents are applied.
pplied i ied is s
These currents are applied after the first set of S-I slopes These currents are applied after the first set
have crossed zero (see paragraph 7-F-45, step g). have crossed zero (see paragraph 7-F-45, step g).
Since both S+ 1 and S-I currents have the same Since both S+ 1 and S-I currents have the same
amplitude, the S + I and S-l slopes should have the amplitude, the S + I and S-l slopes should have the same
magnitude (i.e. zero crossing should occur a magnitude (i.e.
time). time). If a difference in
The S-3
Controller, the DAC is adjusted until the Controller, the DAC is adjusted until the magnitude of the
S + I and S-I slopes S + I
for
Figure 7-F-15. Figure 7-F-15.
7-F.48. Rundown 7-F.48.
ent S + S +
4 slopes are generated the same way it is done for the 4 slopes are generated the same way it is done for the
runup operation (see paragra runup operat
ference is that they only depend on the applied S-4 and ference is that they only depend on the applied S-4 and
S +4 current S +4 currents, not th
the same
generated the same way as the S-0 slope in runup (see generated the same way as the S-0 slope in runup (see
e also
paragraph 7-F-39). paragraph
same circuitry configuration as the S-4 current (see x H · same circuitry configuration as the S-4 current (see x H ·
Figure 7-F-12), b Figure 7-F-12)
resistor values are such that the S-3 current is 1/10 the resistor values are such that the S-3 current is 1/10 the
-1. Thi This s
7-F-14 7-F-14
The currents are also removed w
Once th e the S-I c e S-I curr urrent ents are r s are remo
This current is applied instead o applied instead of no current
happens after after the S-I the S-I slope.
lue as S-l, but in the opposit in the opposite direction.
After er cur Aft curren rent S t S+I +I is is remo
rent S-I is reapplied. is reapplied. This new S-I curren
until zero crossing occurs. ro crossing occurs. After S-I slop
S + 1 is reapplied. After current S + I
S-I is applied, and so , and so on.
During the During the rundown rundown time,
This is This is then used then used to calculat to calculate the
Integrator Offset Integrator Offset Compensation.
slopes from crossing z crossing zero.
+ 2 currents are applied.
ny offsets from the integrator. he integrator. The maximum
are S-3 currents). currents). Time T4 has t
time as T3. T3. The S The S + 2 cu
Then no current (S-0) is applied for the remainder is applied for the remainder
The correct DAC setting DAC setting is determined
zero crossing should occur at a a certain
If a difference in magnitude is noted magnitude is noted by the
and S-I slopes are the same. are the same. This is illustrated in
Rundown Slope Slope Generation. Generation. The S-4 and S +
ion (see paragraphs 7-F-38).
s, not the input curre e input current.
7-F-39). The S-3 The S-3 and S-1
, but ut use use different different resistor
TM 11-6625-3071-14 TM 11-6625-3071-14
also removed within 15 ithin 15
emoved a p ved a posi ositiv tive S
f no current
slope. The current The current has has - -
e direction. The
removed ved, w , with ithin in 5 A 5 ALE
This new S-I current is
After S-I slope e
After current S + I
on. This takes place This takes place
time, a a counter counter in in the the A/D
e the three lea three least st
Compensation. The A/D The A/D
ero. To make To make sure the sure the
applied. The DAC is used The DAC is used
The maximum
Time T4 has the same he same
+ 2 currents are rrents are also
is determined during during
of S-I slopes
same
t a a certain
by the A/D
magnitude of the
This is illustrated in
The S-4 and S +
phs 7-F-38). The only dif- The only dif-
nt. The S-O slope is The S-O slope is
and S-1 currents use currents use the
resistor values. values. The
e S
The
LE
t is
A/D
also
A/D
the
The