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PXI and PXIe

18/03/2022 | General, Hardware, Knowledge

PXI and PXIe (short for PCI(e) eXtensions for Instrumentation) are two of the most important and widely used standards in modern measurement technology. PXI was developed by National Instruments in 1997, but is now a freely available and, most importantly, neutral standard.

In this blogpost, we want to explain what PXI/PXIe is and what benefits these standards offer. But to understand how PXI/PXIe works, we need to go back to the basics of computer systems.

What is a bus?

Among other things, computer scientists are well known for their ability to come up with original names. The term bus also fell victim to this name-giving. A bus is a vehicle that can transport many people at the same time. Each person can get off where he or she wants to.

It is quite similar with a bus in computer science. However, such a bus does not transport people, but data or even electricity. In this context, a bus is similar to an ordinary connector. With an ordinary connector one device can be connected to one other device. A bus, in contrast, allows one device to be connected to several others.

In computer systems, a distinction is made between two types of buses:

  • System buses: The system bus transfers data within the system. The processor of a computer communicates with other parts of the system, such as the central memory, via a system bus.
  • Extension buses: These buses connect external components to the system. Graphic cards or additional memory modules, for example, connect via the expansion bus.

Until a few years ago, PCI was one of the most widely used expansion busses. PCI allowed a transmission bandwidth of 533 MB/s under best conditions. However, since graphics cards and other components require an ever-increasing data rate, the PCIe (PCI express) bus is a standard nowadays. It offers a bandwidth of up to 8 GB/s per channel, which is 16 times more than standard PCI.

PXI and PXIe standards

PXI and PXIe are bus systems developed specifically for measurement applications and are based on PCI and PCIe respectively. This becomes clear if one looks at the written-out name: PCI(e) eXtensions for Instrumentation.

PXI connection

PXI connection

Although the names for PXI and PXIe sound very similar, they differ greatly in terms of hardware. For example, PXIe offers a significantly higher bandwidth and lower latency than PXI due to a serial bus layout. The two systems are also not compatible with each other unless you use so-called PXI hybrid modules. These support both standards.

The additional timing and trigger modules integrated in the PXI/PXIe bus are of great importance for measurement technology. These modules enable synchronization in the nanosecond range or event-controlled measurement recording. In addition, PXI systems usually have rattle-proof and moisture-proof connectors, which makes them particularly robust.

Advantages over other commonly used bus systems in metrology are the high bandwidth, low latency and compact design. Thus, the PXI/PXIe standard is the optimal choice especially for applications with a high channel-count and high data throughput.

In general, a PXI/PXIe system consists of three components:

  • A robust and stable housing
  • A system controller which regulates the data flow of the system
  • External modules such as DAQ cards or power supplies

The combination of performance and robustness make the PXI/PXIe bus the optimal and most versatile bus system in measurement technology.

TRION and TRION(3) measuring cards

We at DEWETRON manufacture high-precision measurement and test systems. We focus on reliability and modularity of the systems. To meet this demand, our TRION DAQ boards use the PXI standard.

However, our TRION(3) DAQ boards go one step further and offer you the PXI express standard. Thus, you are prepared for all possible applications, no matter how data intensive.

Our power analyzers and all-in-one measuring systems also use the PXI/PXIe standard. Here, we have paid attention to backward compatibility of our products. Our DEWE3 measuring systems therefore even offer PXI hybrid connections. So, it does not matter if you want to use a PXI or PXIe module with them.

PXI compatibility

TRION and DEWE3 hardware uses PXIe hybrid

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