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National Instruments Corporation
5-1
5
Calibration
This chapter discusses the calibration procedures for your 6703/6704
device. Calibration is the process of minimizing output errors by making
small circuit adjustments. There are two calibration channels used to make
adjustments to the voltage channels on the 6703/6704. On the 6704, there
are two additional channels used to make adjustments to the current
channels.
Self-Calibration
The 6703/6704 devices perform continuous self-calibration. In addition to
the accessible analog output channels, there are internal calibration
channels that get scanned and refreshed along with all the output channels.
There are two of these calibration channels for the voltage outputs: the
voltage offset channel and the voltage gain channel.
There are also two calibration channels for the current outputs on the 6704:
the current offset channel and the current gain channel. The outputs of these
calibration channels are continuously compared to onboard references, and
the 16-bit DAC offset and gain are adjusted to minimize the errors in the
calibration channels. Since 6703/6704 devices have excellent
channel-to-channel matching of offset and gain errors, minimizing the
errors in the calibration channels also minimizes the errors for all the
voltage and current outputs.
External Calibration
Because of the nature of the 6703/6704 device calibration circuitry, the
only calibration adjustment you must make is to adjust the values of the
calibration channels to account for time- or temperature-related drift of the
onboard reference. These calibration values are loaded into nvRAM at
factory calibration, and you should not need to adjust them for at least one
year after the date of factory calibration, unless you are operating your
device at an extreme temperature.
To perform calibration, you need a voltage and current measuring device
that is much more accurate than your 6703/6704 device. A DMM with an
