Keithley 2182, User Manual, Page: 45 / 339

Voltage and Temperature Measurements 2-5
Performance considerations
The following aspects of operation affect accuracy and speed.
Warm-up
After the Model 2182 is turned on, it must be allowed to warm up for at least 2
1
⁄
2
hours to
allow the internal temperature to stabilize. After the warm-up period, an ACAL must be
performed if the present internal temperature and TCAL differ by more than 1°C. TCAL is the
internal temperature reading stored for the last ACAL (see “ACAL”).
ACAL (calibration)
ACAL is a special front-end gain calibration for the 10mV and 100V ranges. It needs to be
performed whenever the internal temperature and TCAL vary by more than 1˚C. TCAL is the
internal temperature reading at the time of the last ACAL. For example, if ACAL was performed
at 28˚C and the internal temperature changes to 29.1°C, another ACAL will be required to main-
tain specified accuracy. The procedures to measure internal temperature and TCAL are located
after the “ACAL Procedure.”
When the internal temperature and TCAL differ by more than 1°C, Bit 9 in the Questionable
Event Condition Register will set to indicate a questionable ACAL. See “ Status structure ” in
Section 11 for more information.
NOTE Do not confuse this partial calibration (to be performed by the user) with the com-
plete instrument calibration that is to be performed by a qualified service technician.
The complete calibration procedure is located in the Model 2182 Service Manual.
There are two ACAL options. FULL ACAL calibrates the 10mV and 100V ranges, while
LOW-LVL (low-level) ACAL only calibrates the 10mV range. If you are not going to use the
100V range, it is recommended that you only perform LOW-LVL ACAL.
NOTES FULL ACAL requires that there not be any connectors or cables connected to the
LEMO input connector of the Model 2182. Whenever LEMO connections are broken
for an extended period of time, the contacts must be cleaned before reconnecting.
See
“Cleaning input connectors” in Section 1 ( Getting Started ).
For LOW-LVL ACAL, you do not need to remove the input cable, break any
connections, or remove power.
ACAL procedure
Perform the following steps to perform LOW-LVL or FULL ACAL:
1. Press the ACAL key to access the menu.
2. Use or key to display desired ACAL (LOW-LVL or FULL).