SC Express Resource Kit
National Instruments designed the NI SC Express modules for high-performance data acquisition with integrated signal and sensor-specific conditioning. Learn how SC Express incorporates delta-sigma analog-to-digital converters (ADCs) and other unique design technologies to offer increased accuracy, maximum throughput, and best-in-class synchronization for bridge, thermocouple, and high-voltage measurements on PXI Express.
- White Paper: Benefits of Delta-Sigma Analog-to-Digital Conversion
The NI PXIe-4330 bridge input module and NI PXIe-4353 thermocouple input module take advantage of 24-bit delta-sigma ADCs for high-precision strain, bridge-based, and temperature measurements. The differentiating aspects of delta-sigma ADCs are the use of oversampling in conjunction with decimation filtering, and quantization noise shaping to achieve better antialiasing and higher resolution.
- White Paper: SC Express Increases Thermocouple Measurement Accuracy
Thermocouple measurement error can be attributed to many sources including noise, resolution, offset error, and gain error of the device, as well as external noise, thermocouple error, and cold-junction compensation (CJC) error. CJC error is often the largest error in thermocouple measurement devices. The primary factors in CJC errors are thermistor error and isothermal error. The NI TB-4353 isothermal terminal block uses high-accuracy thermistors and has a unique design that allows heat to dissipate evenly between the cold junctions and the thermistors.
- White Paper: Measuring Bridge-Based Sensors with the Ratiometric Approach
Many sensors including strain gages, load cells, pressure sensors, and torque sensors are based on the concept of a Wheatstone bridge. To accurately measure the ratiometric output of a bridge-based sensor both the bridge output voltage and the excitation voltage must be known. The NI PXIe-4330 bridge input module uses circuitry that continuously measures the excitation voltage and applies it as a reference to its ADC. This approach removes the measurement’s dependence on the stability and accuracy of the excitation voltage.
- White Paper: Synchronization Explained
As the latest evolution of the PXI platform, PXI Express has been designed to deliver a higher degree of synchronization to measurement I/O devices while remaining backward-compatible. The 100 MHz differential clock in the PXI Express backplane allows multiple devices to base their sample clocks on the same reference. The backplane trigger lines allow for coordinated triggering of all the devices in the chassis to the same 100 MHz clock edge. If the application requires multiple chassis to be synchronized over large distances, then GPS or IRIG-B PXI timing modules can synchronize multiple chassis by a common clock signal.