Calibration Constants - HP 8340A Service Manual

CALIBRATION CONSTANTS

Introduction
There are three sets of Calibration Constants maintained by the HP 8340A which contain the
calibration data, serial number, option, HP-IB Address, and CHECKSUM information. The
three sets of Calibration Constants are:
Working Data
*
Protected Data
*
Default Data
*
Working Data contains the calibration information that is required for optimum performance
of the HP 8340A. This is the only set of Calibration Constants that is accessed during normal
operation of the HP 8340A. It is stored in RAM on the A60 Processor Assembly and maintained
by battery A60BT1.
Protected Data contains calibration information which is accessed by the instrument if there is a
problem with the Working Data or accessed by the user to update the data. The Protected Data is
typically an exact duplicate of the Working Data and acts as a backup in the event an error occurs
in the Working Data. Protected data is stored in EE-PROM on the A60 Processor Assembly.
Default Data differs from the Working and Protected Data: in that its calibration data is the
average calibration data of several HP 8340As. This is done to ensure that if any HP 8340A goes
to Default Data, it will still be fairly close to its required calibration data for normal operation.
This data is stored in UV-EPROM on the A60 Processor Assembly. The only instance where the
instrument would select Default Data would be if a problem existed with both the Working and
Protected Data.
Instrument and User Access
During normal operation, the HP 8340A will access the Working Data to obtain the calibration
information required for optimum operation of the instrument. In addition to this, the HP
8340A will access the Working Data after an [INSTR PRESET] is initiated, and only to verify
that the CHECKSUM (Cal Constant #99 ) is accurate (see Figure 8A-3, Instrument Preset
Calibration Constant Verifi c ation Sequence).
When [INSTR PRESET] is pressed, the Working Data Cal Constants 1 through98 are summed
and then complemented. The result is then compared with the CHECKSUM. If the two
numbers agree, the instrument continues normal operation. If not, the Protected Data is written
into the Working Data's memory location andthe CHECKSUM test is repeated. If the check­
sum test passes, the data that was in Protected Data
Data and displayed in the ENTRY DISPLAY will be "CALIBRATION RESTORED." If the
CHECKSUMS do not agree, the Default Data is then written to the Working Data. The Working
Data now contains the Default values, the FAULT light on the HP 8340A front panel is lit, and
"CAL DEFAULTED" is displayed. Pressing [SHIFT] [MANUAL] will display the FAULT
diagnostics in the ENTRY D ISP LAY and the CAL light will be fl a shing. (Note that the Protected
Data was not changed. For troubleshooting, this data may be written into the Working Data (per
procedure # 5 below) and viewed (per procedure # 1 below)).
The following describes methods for intentionally changing the
values of the Cal Constants. When a Cal Constant is changed, the
CHECKSUM is automatically updated. If a CAL FAULT occurs and a
Cal Constant is updated, on the next [INSTR PRESEST] (unless
otherwise stated), the CAL FAULT indicator will turn off. This
means that if only a few of the Cal Constants were updated, the
balance will still be using Default Data.
Model 8340A - Service
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Scans by HB9HCA and HB9FSX
now stored as Working and Protected
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