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NI PXIe-4339 and RM-4339 User Guide and Terminal Block Specifications
resulting in a more accurate measurement. In-situ calibration can be performed before and after
test acquisition, or on a periodic schedule, to ensure data validity without physically
disconnecting any inputs from the RM-4339.
During in-situ calibration, the input channels are disconnected internally from the RJ50
connectors and connected to a calibration bus that is driven by the calibration voltage reference
connected to CAL IN±. Through measurement of these channels, any NI PXIe-4339 circuitry
drift since the last full calibration will be available through measurement of these channels.
In-situ calibration performs a verification, but not an adjustment. Therefore, the results from
in-situ calibration will not rewrite the calibration coefficients to the NI PXIe-4339. Instead these
results can be applied to the test setup, test results, or to the NI PXIe-4339 programmatically.
To assist you with starting development of an application with in-situ calibration, an example
program is available for download from the NI Community. Refer to
ni.com/info
and enter
Info Code
exsueg
.
For in-situ calibration, the following connection options are supported through NI-DAQmx as
shown in Table 3.
Table 3.
Per-Channel Connection Options Configurable Through NI-DAQmx Connect
SC Express Calibration Accessory Channels API
Connection Option
Purpose
_cal_channel
Connect a voltage reference provided through CAL IN to the
analog input of each channel.
_remote_sense_
floating
Disconnect RS+/RS-. This option is used during in-situ
calibration of a ratio mode channel. It is used to disconnect the
remote sense of the NI PXIe-4339 module from a connected
bridge sensor. A gain error in the in-situ calibration of a ratio
mode channel will result if remote sense is not disconnected. The
magnitude of the gain error is proportional to the ratio of the lead
wire resistance and the connected sensors resistance.
_disconnect_
excitation
Disconnect EX+/EX-. This option is used during in-situ
calibration of a ratio mode channel. It is used to disconnect the
excitation voltage of the NI PXIe-4339 module from a connected
bridge sensor. Disconnecting the excitation from a connected
sensor allows ratio mode in-situ calibration to be conducted with
all the supported excitation voltage settings regardless of the load
connected to a channels excitation terminals.
Note
: In-situ calibration of ratio mode channels requires the use of paired channels. Refer to
the verification section of the
NI PXIe-4339 Calibration Procedure
for more information
about configuring the NI PXIe-4339 for ratio mode calibration.