Keithley 2790, Reference Manual

Page: 386 / 568

Model 2790 SourceMeter
®
Switch System Reference Manual 16-5
Verification limits
The verification limits stated in this section have been calculated using only the
Model 2790 one-year accuracy specifications, and they do not include test equipment
uncertainty. If a particular measurement falls slightly outside the allowable range, recalcu-
late new limits based on both Model 2790 specifications and pertinent calibration equip-
ment specifications.
Example reading limit calculation
The following is an example of how reading limits have been calculated. Assume you are
testing the 10V DC range using a 10V input value. Using the Model 2790 one-year accu-
racy specification for 10V DC of ± (30ppm of r 5ppm of range), the calculated
limits are:
Reading limits = 10V ± [(10V
×
30ppm) + (10V
×
5ppm)]
Reading limits = 10V ± (0.0003 + 0.00005)
Reading limits = 10V ± 0.00035V
Reading limits = 9.99965V to 10.00035V
Calculating resistance reading limits
Resistance reading limits must be recalculated based on the actual calibration resistance
values supplied by the equipment manufacturer. Calculations are performed in the same
manner as shown in the preceding example, except, of course, that you should use the
actual calibration resistance values instead of the nominal values when performing your
calculations.
For example, assume that you are testing the 10k
Ω
range using an actual 10.03k
Ω
calibra-
tion resistance value. Using Model 2790 one-year 10k
Ω
range accuracy of ± (100ppm of
r 6ppm of range), the calculated reading limits are:
Reading limits = 10.03k
Ω
± [(10.03k
Ω ×
100ppm) + (10k
Ω ×
6ppm)]
Reading limits = 10.02894k
Ω
to 10..03106k
Ω
Restoring factory defaults
Before performing the verification procedures, restore the instrument to its factory
defaults as follows:
1. Press
SHIFT
and then
SETUP
. The instrument will display the following prompt:
RESTORE: FACT.
2. Using either range key, select FACT, then restore the factory default conditions by
pressing
ENTER
.