National Instruments 6711 User Manual

Also see for DAQCard-6715: User manual User manual

Contents

National Instruments 6711 User Manual Manual pdf 13 page image

1-4 | ni.comChapter 1 DAQ System OverviewCalibration CircuitryCalibration is the process of making adjustments to a measurement device to reduce errorsassociated with measurements. Without calibration, the measurement results of your device willdrift over time and temperature. Calibration adjusts for these changes to improve measurementaccuracy and ensure that your product meets its required specifications.DAQ devices have high precision analog circuits that must be adjusted to obtain optimumaccuracy in your measurements. Calibration determines what adjustments these analog circuitsshould make to the device measurements. During calibration, the value of a known, highprecision measurement source is compared to the value your device acquires or generates. Theadjustment values needed to minimize the difference between the known and measured valuesare stored in the EEPROM of the device as calibration constants. Before performing ameasurement, these constants are read out of the EEPROM and are used to adjust the calibrationhardware on the device. NI-DAQ determines when this is necessary and does it automatically.If you are not using NI-DAQ, you must load these values yourself.You can calibrate AO Series devices in the following two ways.Internal or Self-CalibrationSelf-calibration is a process to adjust the device relative to a highly accurate and stable internalreference on the device. Self-calibration is similar to the autocalibration or autozero found onsome instruments. You should perform a self-calibration whenever environmental conditions,such as ambient temperature, change significantly. To perform self-calibration, use theself-calibrate function or VI that is included with your driver software. Self-calibration requiresno external connections.External CalibrationExternal calibration is a process to adjust the device relative to a traceable, high precisioncalibration standard. The accuracy specifications of your device change depending on how longit has been since your last external calibration. National Instruments recommends that youcalibrate your device at least as often as the intervals listed in the accuracy specifications.For a detailed calibration procedure for AO Series devices, refer to the AO WaveformCalibration Procedure for NI-DAQmx document by selecting Manual Calibration Proceduresat ni.com/calibration.Cables and AccessoriesNI offers a variety of products to use with Analog Output Series devices, including:• BNC accessories• Connector blocks with screw terminals• I/O connector cables