Distribution of Gain Between an SCXI Module and an E Series Data Acquisition (DAQ) Device Hardware: SCXI
Problem: I am using an E Series DAQ device and an SCXI module with LabVIEW. What gain settings do these types of hardware use in various situations? Solution: The two types of SCXI modules that apply gain are jumper-configurable modules and software-programmable modules. Here are some tips on how gain is distributed between E Series DAQ devices and SCXI modules using LabVIEW. Jumper-configurable modules require that you match the SCXI gain settings in Measurement & Automation Explorer (MAX) with the jumpered gain settings in hardware. LabVIEW stores the gain settings configured in MAX and uses those settings to correctly scale acquired data. LabVIEW uses the input limits cluster of the Analog Input (AI) VIs to determine how much overall gain is required. Finally, based on the amount of gain the SCXI hardware applies and the overall gain required, LabVIEW decides how much onboard gain is required on the DAQ device to complement the jumper-selected SCXI gain. You can adjust the gain on software-programmable SCXI modules exclusively in MAX. LabVIEW considers the gain settings in MAX as the default and applies this amount of gain in SCXI whenever the input limits setting in LabVIEW is unwired or contains a value of 0 for both upper and lower limits. When the input limits are modified to use non-zero limits, LabVIEW chooses the most appropriate SCXI gain to match the input limits. The gain on software-programmable SCXI modules is maximized before LabVIEW applies any gain on the DAQ device. If the module gain is software programmable (as with the SCXI-1141, for example), LabVIEW boosts the module gain as high as possible until it needs to apply gain on the E Series device. If the module is jumper configurable, you must make sure the gain settings in MAX match the jumper settings. LabVIEW applies SCXI gain based on the module gain settings in MAX. If additional gain is required, LabVIEW applies this gain on the E Series device. LabVIEW always returns a value that has been scaled down based on the gain/attenuation that was selected. For example, if you measure 110 volts with an SCXI-1327 terminal block set to 100:1 attenuation, using a gain of 1 on both the SCXI module and DAQ device causes LabVIEW to report 110 volts (not 1.1 volts) because LabVIEW records all information set in MAX, including which SCXI accessories are in use. Related Links: KnowledgeBase 1ABBOQVK: How Do I Set the Gain for My Analog Input Channels in LabVIEW? Attachments:
Report Date: 09/13/2000 Last Updated: 06/05/2002 Document ID: 21CDIA4U |
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