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BASIC DMM OPERATION
2.6.1 Warm Up Period
The Model 196 is usable immediately when it is first turned
on. However, the instrument must be allowed to warm up
for at least~ two hours to achieve rated accuracy.
2.6.2 Zero
The zero feature serves as a means of baseline suppression
by aIlowing a stored offset value to be subtracted from
subsequent readings. When the ZERO button is pressed,
the instrument takes the currently displayed reading as a
baseline value. All subsequent readings represent~the dif-
ference between the applied signal level and the ~stored
baseline.
A baseline level can be established for any or all measure-
ment functions and is remembered by each function. For
example, a 1OV baseline can be established on DCV, a 5V
baseline can be established on ACV and a 1Okll baseline
can be established on OHMS. Theses levels will snot be
cancelled by switching back and forth between functioti.
Once a baseline is established for a measurement function,
that stored level will be the same regardless of what range
the Model 196 is on. For example, if 1V is established
as the baseline on the 3V range, then the baseline will also
be 1V on the 30V through 30lV ranges. A aem baseline level
canbeaslaigeasfullrange.
~~
NOTE
The followirg discussion on dynamic range is
based on a display resolution of 6% digits. At 5'/zd
resolution, the number of counts would be reduced
by a factor of 10. At 4Yzd resolution, counts would
be reduced by a factor of 100 and 3%d resolution
would reduce counts by a factor of 1000.
By design, the dynamic measurement range of the Model
196, at 6%-d@
resolution, is M)60000 counts.1 With zero
disabled, the displayed reading range of the instrument is
*303ooOO counts. With zero enabled, the Model 196 has
the capability to-display ~606OCOO counts. This increased
display range ensures that the dynamic measurement range
of the instrument is not reduced when using a zero baseline
value. The following two examples will use the maximum
allowable zero values (3030000 counts and -3030008
counts) to show that dynamic measurement range wilI not
be reduced. It is important to note that the increased display
range does not increase the maximum allowable input level
to the instrument. For example, on the 3V range, the Model
196 will always overrange when more than k3.03V is con-
nected to the input.
Example l-The instrument is set to the 3V DC range and
a maximum -3.03OOOOV is established as the zero value.
When -3.03OOOOV is connected to the input of the Model
196, the display will read O.OMlOOClV.
When +3.03OCEOV is
co.nnected to the input, the display will read +60600ooV.
Thus, the dynamic measurement range of the Model 196
is OV to 6.06V, which is 6060000 counts.
Example 2-Ihe
instrument is still set to the 3V DC range,
but a maximum +3.03oOOOV ia the zero level. When
+3.03oO~CGV
is connected to the input of the Model 196, the
display will read O.O@XtOOV When Y3.0~
is connected
to the input, the display will read -6.06OOOCV. Thus the
dynamic measurements range of the instrument is -6.06V
to OV, which is still 6060000 counts.
Zero Correction-The Model 196 must be properly zeroed
when using the 3OOmV DC or the 3OOB range in order to
achieve rated accuracy specifications. To use ZERO for zero
correction, perform the following steps:
z
2.
3.
4.
5.
Disable zero, if presently enabled, by pressing the
ZERO button. The ZERO indicator will turn off.
Select the 3oOmV DC or the 30022 range.
Connect the test leads to the input of the Model 196 and
short
them
together.
If
four-wire
resistance
measurements are to be made, connect and short all four
leads together. Allow any thermals to stabilize.
Note: At5% and 6%~digit resolution, low level measure-
ment techniques need to be employed. Use Kelvin test
leads or shielded test leads. See paragraph 2.6.5 for low
level measurement considerations.
Press the ZERO button. The display will read zero.
Remove the short and connect thetest leads to the signal
or resistance to be measured.
Note: Test lead, resistance is also~ compensated for when
zeroing the 3OO'J range with the above procedure.
Baseline Levels-Baseline
values can be established by
either applying baseline levels to the instrument or by set-
ting baseline values with the front panel ZERO program.
paragraph 27'15 contains the complete procedure for using
the ZERO program. To establish a baseline level by apply-
ing a level to the Model 196, perform the following steps:
1. Disable zero, if presently enabled, by pressing the ZERO
button. The ZERO indicator will turn off.
2. Sele&a function and range that is appropriate for the
anticipated measurement.
3. Chnect
the desired baseline level to the input -of the
Model 196 and note that level on the display
2.7
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