Through plug and play connectivity and almost ubiquitous USB ports on modern PCs and laptops, USB has become a popular choice for controlling independent instruments. As more and more instrument manufacturers begin to include USB ports on their devices, it is important to understand several issues surrounding USB to ensure the lifespan of the test connection system.

1、 USB 3.0 does not necessarily mean ultra high speed

Many testing applications today require a large amount of data to be transferred from the instrument to the PC. When selecting an instrument, you need to know the transfer rate supported by the PC. The USB standard provides four data transfer rates:

1. Low speed -1.5 Mb/s data transmission. Devices such as mice and keyboards typically use this minimum transmission speed. This is part of the original USB 1.0 standard.

2. Full speed -12 Mb/s data transmission. Before the launch of Hi Speed USB in 2000, it was the fastest transfer speed for USB. This is also part of the original USB 1.0 standard.

3. High speed -480 Mb/s data transmission. The high-speed transmission rate adopts the high-speed USB standard (USB 2.0), making USB a viable choice for sending large amounts of data such as audio and video.

4. Ultra high speed -1Gb/s data transmission. This was introduced with the USB 3.0 standard.

Each continuous USB standard maintains backward compatibility with the old standard. Although the USB 2.0 specification introduces high-speed transfer rates, it also maintains backward compatibility with low-speed rates, just like the previous USB 3.0. Therefore, devices are usually referred to as USB 3.0 compatible and only support low, full, and high-speed transfer rates. When purchasing a new instrument, please look up the term "ultra fast USB" to ensure that the instrument can support the fastest transfer rate.

2、 Instrument control requires a USB B-type device connection port

The instrument can display two different types of USB ports, A-type host port and B-type device port. A-type host ports are more commonly recognized by their flat and slender appearance, but you cannot use them for instrument control. You can only use these connectors to control other USB devices, usually by saving data to a USB memory stick or adding mouse and keyboard support to the instrument. To allow control of instruments from a PC, you need a B-type device port that is recognized through a more square shape. When checking the instrument data sheet, please refer to the USB device port or USB instrument control reference to ensure that you can remotely control the instrument.

3、 USB testing and measurement classes simplify application development

Programming USB instruments may be a major challenge due to their non-compliance with the set communication protocol. To address this issue, the USB Implementers Forum (USB-IF) has defined a specific device class called USB Test and Measurement Class (USBTMC). Designed to simulate the IEEE 488.1 standard, you can program instruments that support USBTMC, just like their GPIB counterparts. This device class greatly simplifies instrument control, as you can use industry standard application programming interfaces (APIs) such as NI-VISA to send and read instrument commands without implementing lower level communication protocols.

For devices that do not support USBTMC, you need to use the driver provided by the supplier or program the device in USB RAW mode. NI-VISA supports communication in USB RAW mode, but you need to contact the instrument supplier for specific information on their communication protocol.

4、 You can reduce (or eliminate) setup time through plug and play connections

One of the biggest advantages of USB compared to other buses is its support for plug and play connections. Using tools such as NI Measurement&Automation Explorer (MAX), USBTMC instruments can be automatically detected and configured. Unlike Ethernet/LAN, there is no need to enter an IP address or use a company firewall to connect the instrument. USB plug and play connectivity has also facilitated the development of interactive tools that can be loaded immediately when connecting USB instruments.

Here is an example: National Instruments SignalExpress Tektronix Edition. After connecting a compatible Tektronix instrument to a PC through USB, the PC immediately detects the connected instrument and displays an automatic playback dialog box. With just a click of the mouse, the NI SignalExpress Tektronix version can connect to the instrument, start displaying real-time data collection, and provide remote instrument control.

5、 Industry standard software interfaces help ensure the lifespan of testing systems

Although USB is the popular communication bus today, the history of the computer industry suggests that today's popular technology may be outdated tomorrow. Due to this history, even if there are changes in the communication bus, it is important to make decisions to ensure the lifespan of the testing system. You can use Virtual Instrument Software architecture (VISA) and NI LabVIEW Plug and Play Instrument Driver to do this.

6、 You can obtain a USB connection from the current instrument

By using a GPIB converter, you can gain many advantages of USB instrument control, such as plug and play connectivity, ease of use, and easy access to USB ports while using the current GPIB instrument. You can achieve this goal through devices like NI GPIB USB HS+, which is a high-speed USB device that can convert any USB port into a fully functional GPIB controller. Since you can use the current instrument, you can save hardware and software investment and development costs without the need to write a new instrument.