HP 3455A - Page 26

Seclion (II Model 345SA
displayed is + 200,000 and the smallest number is
-200.00.
If the magnitude of
the display exceeds
200,000,
either
a
“
+ LL” or a **-LL” is displayed.
Therefore, the
“y”
and “z” constants must be
chosen
so
that when “x" (the reading) is equal to the upper
limit, the display is + 200,000 and
when “x" is equal to
the
lower limit,
the
display
is
-200,000. This can be ac-
complished as follows;
When
X
=
the
Lower Limit,
the
DISPLAY should
=
•
200,000
When X
=
the Upper Limit, the DISPLAY should
»
+
200,000
therefore,
-200,000
= Lower
Limit
•
z
y
and + 200,000
=
Upper
Limit
-
z
y
This
leaves two equations
to
solve for
the
unknown
”y”
and "z” constants.
The two
constants
can
be
found the
following way:
3-23.
Enter
end Store.
3-24.
The "Y” and “Z” ENTER keys have two func-
tions.
When
one of the enter keys is pressed, the number
presently stored in the
respective
memory register is
displayed
on the front panel readout. This allows the
operator
to check
the
contents
of
the “Y” or “Z”
memory registers. Pressing
the
enter
key also
“shifts”
the front
panel
keyboard, disabling all keys except those
labeled in
blue. These keys can
now
be used to enter the
desired values to be stored
in
the
"Y” or “Z” memory
registers. As the
value
is entered it is displayed on the
from panel readout. Numerical values from .OOOCXX) to
+ or
-
199,999.9 may be entered in either the Y or Z
registers.
3-25.
The STORE
keys
are
used
to transfer
the
number
presently being displayed in the “Y” or “Z” memory
registers and to return the voltmeter
to
normal opera-
tion.
3-26.
The
following
describes
how
the ENTER and
STORE
features
may be used:
-200,(XX)
(y)
+ 200,000
(y)
0
therefore, z
200,000
Lower Limit
-
z
Upper Limit
•
z
Lower Limit + Upper Limit -2Z
(add these two equations)
Upper Limit + Lower Limit
2
Upper Limit
•
z
y
200,000
(y)
=
Upper Limit-
UPP«r
Limit +
Lower
Limit
2
Upper Limit
•
Lower
Limit
2
and,
y
Upper
Limit
-
Lower Limit
400,000
The
following
is an example
of how
to use this
math
technique.
In
this example a DC voltage is measured
and compared with a Lower Limit of 10
volts
and an
Upper
Limit of 30 volts:
y
B
Upper Limit
-
Lower
_
30-10
_
qqq
()5
400,000 400,000
,
_
Upper
Limit + Lower Limit
_
30 +
10
b
20
2
2
By
entering .00005 into the
“y”
register and 20 into the
“z”
register, and then pushing the SCALE and
DCV
buttons,
the
3455A becomes a limit testing
DVM.
If the
input exceeds 30
volts
a
“
+ LL” is displayed, and if the
input is less than 10
volts
a “-LL” is
displayed. If the in-
put is
within the limits set. a number is displayed.
a.
To view the value presently in
memory,
press
the
ENTER key of the appropriate register (ENTER Y or
ENTER
Z). To
return
this number to memory, press the
STORE key of the appropriate register.
b.
To enter
a
new number,
press the ENTER key of
the
register
to
receive
the number. Enter the desired
number
into the
display
by pressing the keys
labeled
in
blue. Store the number
entered by pressing the
STORE
key of the appropriate register.
c. To enter a measurement
value presently being
displayed,
press the
STORE key of the desired
register
(Y
or Z).
NOTE
The operation
of
the
ENTER and STORE
keys are not
mutually exclusive. That is,
the
number being displayed may be
stored in
either the Y or Z
register independently
of
the
register selected by the ENTER
keys.
3-27.
High
Resolution Mode.
3-28.
When the 3455A is used
in the HIGH RESOLU-
TION mode, the instrument
changes from a
5-1/2
digit
measurement to a
6-1/2
digit
measurement. This
changes the
measurement resolution from
10
parts/1.5
million
(5-1/2 digit mode) to
1
part/1.5
million
(6-1/2
digit mode). The
integration period
will
also
change
from 1/60
second (1/50 second for 50
Hz operation) to
8/60 second (8/50
second for 50 Hz
operation). The
High Resolution mode
cannot be used in the AC
mode
or the
.1 V DC and 1 K ohm ranges.
The reading rate in
the
DC and Ohms mode
will
also
increase when the
High Resolution
function
is
turned off. Table
3-1 gives
the
various reading rates of the DC and Ohms
functions
34