Table Of Contents

Internal Channels for SC Express Devices

Last Modified: November 16, 2017

On an NI 4300 or NI 433x device, you can either acquire a signal present on the I/O connector, or you can acquire an onboard signal, via an internal multiplexer. The channels available on this multiplexer are typically used for calibration purposes, but you can also sample them as you would a physical signal present on the I/O connector. To read from one of these internal channels, you must use one of the device's AI physical channels (Dev1/ai0 through Dev1/ai7) when creating the virtual channel. The physical channel specifies the ADC for the internal channel. You can then set the appropriate string value on the Input Source channel attribute/property.

On the NI 4353, you can acquire internal channels by specifying their names for the physical channels input of the DAQmx Create Channel VI/function.

Internal Channels for the NI 4302 and 4303

Input Source Description
_cjtemp The temperature read by a digital temperature sensor located on the TB-4302 accessory. This channel is used for cold-junction compensation.

Input Sources for the NI 4300 and 4310

Input Source Description
_external_channel The source of the AI channel is the device input connector, or an accessory connected to the device connector.
_aignd_vs_aignd The source of the AI channel is the onboard ground signal.
_calref_vs_aignd The source of the AI channel is the onboard reference signal.
_calSrcHi_vs_aignd The source of the AI channel has the positive terminal connected to the onboard calibration PWM and the negative terminal connected to the onboard ground reference.
_aignd_vs_calSrcHi The source of the AI channel has the positive terminal connected to the onboard ground reference and the negative terminal connected to the onboard calibration PWM.
_calref_vs_calSrcHi The source of the AI channel has the positive terminal connected to the onboard reference signal and the negative terminal connected to the onboard calibration PWM.
_aipos_vs_calSrcHi The source of the AI channel has the positive terminal connected to the positive terminal of the device input connector and the negative terminal connected to the onboard calibration PWM.
_aineg_vs_calSrcHi The source of the AI channel has the positive terminal connected to the negative terminal of the device input connector and the negative terminal connected to the onboard calibration PWM.

Internal Channels for the NI 4309

On the NI 4309, you can acquire internal channels by specifying their names for the physical channels input of the DAQmx Create Channel VI/function.

Input Source Description
_aignd_vs_aignd<0..7> A differential terminal with the positive and negative terminals both connected to the ground reference; using the specified ADC <0..7>. This channel is used to measure the autozero offset of individual ADCs.
_calSrcLo_vs_aignd<0..7> A differential terminal with the positive terminal connected to the calibration PWM and the negative terminal connected to the ground reference; using the specified ADC <0..7>. _calSrcLo is the divided down version of _calSrcHi.
_7VRef_vs_aignd<0..7> A differential terminal with the positive terminal connected to the onboard 7V reference signal and the negative terminal connected to the ground reference; using the specified ADC <0..7>.
_calSrcHi_vs_aignd<0..7> A differential terminal with the positive terminal connected to the onboard calibration PWM and the negative terminal connected to the ground reference; using the specified ADC <0..7>.

Input Sources for the NI 4330 and 4331

Input Source Description
_external_channel The source of the AI channel is the device input connector, or an accessory connected to the device connector.
_aignd_vs_aignd The source of the AI channel is the onboard ground signal.

Input Sources for the NI 4339

Input Source Description
_external_channel The source of the AI channel is the device input connector, or an accessory connected to the device connector.
_paired_channel_excitation The source of the AI channel is the paired channel's internal excitation. The channel pairs are ai0 and ai1, ai2 and ai3, ai4 and ai5, ai6 and ai7.
_aignd_vs_aignd The source of the AI channel is the onboard signal ground.

Internal Channels for the NI 4353

On the NI 4353, you can acquire internal channels by specifying their names for the physical channels input of the DAQmx Create Channel VI/function.

Input Source Description
_cjtemp0 through _cjtemp7 A differential terminal with the positive and negative terminals connected to a temperature sensor located on the accessory. These channels are used for cold-junction compensation. The mapping between analog input channels and cold-junction compensation channels depends on the type of installed accessory.
_aignd_vs_aignd0 A differential terminal with the positive and negative terminals both connected to the ground reference, using the ADC that is used for even-numbered channels (ai0, ai2, ai4, and so on). This channel is used to measure the autozero offset of even-numbered channels.
_aignd_vs_aignd1 A differential terminal with the positive and negative terminals both connected to the ground reference, using the ADC that is used for odd-numbered channels (ai1, ai3, ai5, and so on). This channel is used to measure the autozero offset of odd-numbered channels.

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