What is the difference between SCXI and PXI?

Answer 1

I work for National Instruments. NI is one of the companies that defined PXI. PXI stands for PCI eXtensions for Instrumentation. It is like the PCI bus, but extended. This means that extra connections are available to share signals between multiple PXI peripherals.

SCXI stands for Signal Conditioning eXtensions for Instrumentation. Signal Conditioning is the general term for the process of making a signal more useful by improving its precision, accuracy, or signal-to-noise ratio.

Think about a sensor/transducer such as a thermocouple. In order to get quality temperature readings, you need to amplify the thermocouple signal. You should also filter out high frequencies, because while noise is high-frequency in most environments, temperature changes almost always happen very slowly.

SCXI can also handle switching, and has some multiplexer's in the background so that a separate ADC can capture the conditioned signals.

So, to put these two together, a real-world signal from a transducer goes into SCXI, which might then send the conditioned signal into a DAQ board in a PXI system.

Another key difference is that a PXI bus directly communicates to an operating system on a computer, while SCXI only does things to signals and passes them on to DAQ devices.