3-20 Basic DMM Operation Model 2750 Multimeter/Switch System User’s Manual
CAUTION Front panel inputs — Do not apply more than 1000V peak between
INPUT HI and LO, or instrument damage may occur.
Model 7700 switching module — Do not apply more than 300V DC or
RMS between input high (H) or input low (L), or switching module
damage may occur.
5. If using a switching module, perform the following steps to close the desired chan-
nel. Keep in mind, that for Ω4 measurements, you will close the primary (INPUT)
channel (1 through 10). The paired channel will close automatically.
a. Press the CLOSE key.
b. Use ,
, Δ , and ∇ to key in the channel number and press ENTER. The
previously closed channel(s) (if any) will open, and the specified channel (or
channel pair) will close.
NOTE While in the normal measurement state, you can use the and keys to close
channels. In general, each key press will open the presently closed channel, and
then close the next higher or lower channel.
6. Observe the displayed reading. If the “OVERFLOW” message is displayed, select
a higher range until a normal reading is displayed (or press AUTO for autorang-
ing). For manual ranging, use the lowest possible range for the best resolution.
7. To measure other switching channels, repeat steps 5 and 6.
8. When finished, press OPEN if there is a channel closed.
Offset-compensated ohms
The presence of thermal EMFs (V
EMF
) can adversely affect low-resistance measurement
accuracy. To overcome these unwanted offset voltages, you can use offset-compensated
ohms (OCOMP). Offset-compensated ohms measurements can be performed on the 1Ω,
10Ω, 100Ω, 1kΩ, and 10kΩ ranges for the Ω4 function. It cannot be done on the Ω2
function.
NOTE The various instrument operations, including OCOMP, are performed on the
input signal in a sequential manner. See “Signal processing sequence,”
page D-2, for details. It includes a flowchart showing where in the processing
sequence that the OCOMP operation is performed.
For a normal resistance measurement, the Model 2750 sources a current (I) and measures
the voltage (V). The resistance (R) is then calculated (R=V/I) and the reading is displayed.
For offset-compensated ohms, two measurements are performed: one normal resistance
measurement, and one using the lowest current source setting.
2750-900-01.book Page 20 Wednesday, August 3, 2011 7:56 AM
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