HP 3478A Technical Manual page 107

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3478A

Figure 7-F-13. Slope S+0 and

Figure 7-F-13.

Slope S+0 and S-0 Generation

ference is that paths Y1 and Y2 are switched when the

slopes are switched (YI to ground and Y2 to -Vref, or Y2

to ground and Y1 to -Vref).

to ground and Y1

to -Vref).

7-F-40. Runup

7-F-40.

Runup Time.

Time. The runup time changes with the

number of digits selected.

number of digits se

lected. For the 3

time is 1/600 second (for both the 60Hz and the 50Hz

options) and is called .1

options) and

is called .1 PLC (Power

the 4 1/2 Digit mode, the time is 1/60 second (1/50

second for the 50 Hz optio

second for the

50 Hz option) and is called

1/2 Digit mode

1/2 Digit mode is different.

is different. In this mode,

for the runup time with the A/D operation repeated ten

times. The resultant ten

times.

The resultant ten readings are the

the answer becomes a single reading.

7-F-41.

7-F-41. Digit

Digit Generation.

Generation. When the 3478A is in the 4

1/2 and 5 1/2 Digit mode, the first two significant digits

(of the reading) are determined during

(of the reading) are determined

Digit mode, only

Digit mode,

only the first

the first digit is de

down, the three least significant digits are determined in

all modes.

all modes. A total of 5

A total of 5 /2 digits are de

/2 digits are developed in both the

51/2 and 4/2 digit

51/2 and

4/2 digit modes.

modes.

displayed in the 41/2 digit mode, the last digit in the

mode is rounded off to the next higher digit.

S-0 Generation

The runup time changes with the

For the 3 1/2 Digit mode,

1/2 Digit mode, the

PLC (Power Line Cycles).

Line Cycles). For

n) and is called 1 PLC.

1 PLC. The 5

In this mode, 1 PLC is used

1 PLC is used

readings are then averaged and

n averaged and

When the 3478A is in the 4

during runup.

runup. In t

In the 3

digit is determined.

termined.

veloped in both the

Since only

Since only 412 digits

412 digits are

Figure 7-F-14.

Figure 7-

7-F-42.

voltage at the A/D Converter's input is removed and the

input is the

input is then connected t

tion then starts.

tion then sta

least significant digits of the 3478A's reading.

7-F-43.

7-F-43. After runup,

the integrator with its amplitude and polarity dependent

on the last current applied (S + 4 or S-4) and the input

voltage (applied during runup).

voltage (applied

the remaining voltage, the least significant digits

the remaining voltage, the least significant digits can then

be determined.

determined.

applying various currents to the integrator and counting

the number of of times the currents have to be applied

for the resultant output slopes of the integrator to cross

zero.

7-F-44. The currents applied

7-F-44.

the S-4, S + 4, S-3, S + 2, S-1, and S + 1 currents and

the resultant output slopes are the S-4, S + 4, S-3, S + 2,

S-1, and S + 1 slopes.

S-1, and S +

4, etc.) are applied (in the given

4, etc.) are applied (in the given order) to the integrator a

set number of t

set number of times until zero cro

exception is the first S4 current (see paragraph 7-F-45

step c).

step c). The first and second

the S-4 and S + 4 currents, r

the S-4 and

have the same value as the S-4 and S + 4 currents used

the

in the runup operation, but ar

in the runup

S-4 and S + 4 slopes are each 15 ALE cycles long (30

For

ALE cy

ALE cycles in

cles in runup) and

next currents applied (in order) are the S-3, S + 2,

next currents applied (in order) are the S-3, S + 2, and S-

The 5

1 currents, with S- slopes applied between them.

7-F-45.

periods, as shown in

periods, as shown in Figure 7-F-14.

for the following explanation on the rundown opera- tion.

a. a. When r

remaining voltage on the integrator is determined by the

A/D Controller (U462).

A/D Controller (U46

he 3 ½ ½

output state of the A/D comparator (CMP output at U403

In run-

pin 11). A high output level show

pin 11).

a low level shows a negative voltage.

are

F-14. Rundown Slope

Rundown Slopes s

7-F-13

Rundown.

When runup is completed, the

n connected to ground.

o ground. The rundown opera-

rts. Rundown is used to dete

Rundown is used to determine the three

After runup, a voltage

a voltage (or charge) re

during runup). By obtaining

The

The voltage

voltage value

The currents applied to the int

to the integrator are

1 slopes. Each one of the currents (S4,

Each one of the currents (S4, S +

imes until zero crossing occurs.

The first and second set of currents

set of currents applied are

S + 4 currents, respectively.

espectively. These currents

operation, but are applied half as long.

e applied half as long. The

runup) and are called

are called half-ramps.

Rundown

Rundown time

time is separ

is separated

Figure 7-F-14. Refer

When rund

undown

own sta

starts

rts, th

2). The polarity is det

The polarity is determined by the

A high output level shows a positive voltage and

TM 11-6625-3071-14

The rundown opera-

rmine the three

(or charge) remains on

mains on

By obtaining the value of

the value of

can then

value is obt

is obtained

ained by

egrator are called

called

S +

order) to the integrator a

ssing occurs. The only

The only

applied are

These currents

The

half-ramps. The

The

and S-

ated into

into five t

five time

ime

Refer to to the

the figure

figure

, the pol

e polari

arity ty of th

of the e

ermined by the

s a positive voltage and

HP 3478A Technical Manual page 107

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