Calibration Commands
The Calibration commands provide for four levels of calibration:
•
A/D Calibration: In these procedures, an external multimeter is
used to determine the actual voltage or resistance values of the
HP E1413’s internal calibration sources. The known values are then
sent to the HP E1413 where they are stored and used to perform
internal A/D calibration. These procedures each require a sequence
of several calibration commands.
•
Channel Calibration: This function corrects for offset and gain
errors for each module channel. The internal current sources are also
measured. This calibration function corrects for thermal offsets and
component drift for each channel out to the input side of the Signal
Conditioning Plug-on (SCP). All calibration sources are on-board
and this function is invoked using the single command
CARDCAL
.
•
A/D Converter Zero: This function quickly compensates for any
short term A/D converter offset drift. This would be called the
auto-zero function in a conventional voltmeter. In the HP E1413,
where channel scanning speed is of primary importance, this
function is performed only when the
ADZERO
, and
CARDCAL
commands are executed.
ADZERO
is much faster than
CARDCAL
.
•
Channel Tare: This function (
TARECAL
) corrects for voltage
offsets in external system wiring. Here, the user places a short
across transducer wiring and the voltage that the module measures is
now considered the new “ zero” value for that channel. The new
offset value can be stored in non-volatile calibration memory
(
STORETAR
) but is in effect whether stored or not. System offset
constants which are considered long-term should be stored. Offset
constants which are measured relatively often would not require
non-volatile storage.
Appendix D
Register-Based Programming 363
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