HP 2040D - Manual (Page 9)

Series 2040 Test System
Series 2040 Maintenance Manual V2.00 Selftest & Calibration
8
SELFTEST AND CALIBRATION OVERVIEW
Calibration on the Series 2040 Functional Test System is completely
automated. All calibration is based on high precision references built into the
system Testhead and the Selftest Assembly. A high precision Temperature
Compensated Crystal Oscillator (TCXO) on the Time Measurement System
Board (TMS) is used as a frequency/time reference. A precision digital to
analog converter (TDAC) contained within the Selftest Assembly is used as a
voltage reference for system calibration.
Purpose Of Calibration
Calibration of the functional tester is necessary to obtain gain and offset terms
for all signal paths that exist within the system, and to determine timing for the
MDE’s (Measurement Display Electronics) sweeps, delays, triggers, and
measurement mark. Since potentiometers are used in only a few instances
where factory calibration is required, the majority of the calibration is done by
taking measurements and calculating calibration terms which can be
referenced at a later time. These terms are used by the hardware functional
calls to account for gains, offsets, and timing discrepancies, and their use is
transparent to the user.
In all calibration programs, limits are set on what values any given calibration
term may take on. If a calculated value is outside of the allowable range, a
failure will result and be displayed/printed to the designated output device .
When To Calibrate
Selftest is the best guide to determine if calibration is required. The battery of
Selftest programs is designed to test all functions of the 2040 to their
specifications. If any failures occur during Selftest (especially borderline
failures), calibration should be carried out before proceeding to troubleshoot
the system.
Running through Selftest periodically can tell you if calibration is or is not
required. If you find that all Selftest programs run without failures, there is no
need to recalibrate any portion of the tester. The recommended guideline is to
calibrate every 3 months.
Whenever a temperature change of more than five (5) degrees Celsius occurs
or a Testhead board swap is made, the 2040 should be recalibrated.