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OPERATION
3.10.1 Zeroing
From an Applied
Signal
To store the zero offset value from a" applied signal, per
form the following
procedure.
1. Select the desired channel.
2. Cancel the zero mode if presently
enabled.
3. Select a range that is consistent
with the anticipated
measurement.
4. Connect the signal that is to be used as a" offset value
to the VOLTAGE INPUT jack of the selected channel.
5. Press the ZERO button to enable the zero mode. If there
is no valid reading on the display, the zero mode can-
not be enabled.
6. Disconnect
the offset signal from the instrument
and
connect the signal to be measured in its place. Subse-
quent measurements will be the difference between the
suppressed
value and the applied signal.
WARNING
The
voltage
on the
input
terminals
may
be
larger
than the displayed
value.
For example,
if
a 175V zero offset
is stored,
an applied
voltage
of 200V will result
in a displayed
reading
of on-
ly 25v.
7. To cancel the zero mode, simply press ZERO a second
time. The stored v&c
will be retained for use by the
zem value mode discussed below.
3.10.2 Keying
In the Zero Value
The zero feature may also be used by keying in the zero
offset from the front panel. This mode is entered by press-
ing SHIFT ZERO VAL and then using the data entry keys
to key in a new value. Once the value is entered, the zero
mode will remain in effect until zero is disabled with the
ZERO key. The ZERO indicator will be on when the zero
mode is enabled.
in the appropriate
emv message.
Also, the instrument
will
display a NMBR TOO SMALL error if you attempt to pro-
gram a zero value smaller than the resolution
of the AID
converter (1OpV).
As with the ZERO key, ZERO VAI. is inoperative when the
instrument
is in the dual-channel
display mode.
Program a zero value from the front panel as follows:
1. Press SHIFT ZERO VAL to enter the front panel zero
mode. The instrument
will prompt with the presently
programmed
value.
2. Using the data keys, key in the desired value. For ex-
ample, program a zero value of 255mV as follows. Press
: 2, 5, 5, mv.
3. The new zero value will be programmed, and the ZERO
indicator
will be on.
4. To cancel the programmed
zero mode, simply press the
ZERO key. The presently
programmed
zero value will
be retained for use when ZERO VAL is pressed again.
3.10.3 Zero Mode Considerations
The display can show up to +99999 counts in the zero
mode, unlike
a normal
"on
zeroed reading,
which
is
limited to -32,768, +32,767 counts. For example, if a zeroed
value is -6OOmV, and the applied signal is +3OO.OOmV, the
display will show .ROOOOV.
If the instrument
is in the autorange mode, it will move
up range If the *99,999 count limit is exceeded. Once zero
is enabled, setting the range lower than the zeroed value
will create a" overrange condition.
The Model 194 will
display the OFLO message in this case. Note that the in-
strument
must be triggered to effect a range change.
When using zero with a mathematical function, the zeroed
value is subtracted from the reading after the mathematical
operation
is performed.
The allowable range for the entered zero parameter is be-
tween -200 and +2OOV. Exceeding these values will result
3.18
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