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Microlink Measurement and Control Systems

Technical Notes: USB


USB Plug

The USB (universal serial bus) is a relatively recent way to connect instruments and devices to the PC. Most new computers have one or two USB ports, in addition to the familiar RS232 (COM) and parallel ports. You can use the USB ports for many peripherals, including digital cameras, printers and data acquisition and control units like the Microlink 751.


Why use the USB for Data Acquisition?

The USB is extremely convenient for data acquisition for several reasons.

  1. The equipment can obtain power from the USB; it doesn't need to be battery powered or plugged into the wall. This makes USB ideal for portable data acquisition with a laptop.
  2. Using a USB hub you can connect many devices to one socket - letting you easily expand your system should requirements grow.
  3. USB ports are provided on most new PCs - no need to open the computer and install adaptor cards.
  4. You can plug in and unplug your equipment without switching off your computer or even restarting Windows.
  5. The USB cable can be up to 5 m long. However, using USB hubs between cables you can reach 30m.
  6. Faster speeds than those allowed by RS232 connections are achievable
  7. You can use USB devices alongside existing data acquisition equipment (such as instruments that plug directly into the RS232 port).

What about older PCs?

If your PC does not have a USB port you can buy a PCI-based card which provides one. However, you need to be running Windows 98SE or Windows 2000. (Early releases of Windows 95 do not support USB, later releases have some support but it's better to use Windows 98SE or 2000.) You can test whether your PC is USB compatible by visiting www.usb.org and downloading their evaluation utility program.

If you don't wish to upgrade your machine there are many other ways to connect data acquisition equipment to computers, such as Ethernet, RS232, RS485 or GPIB.


Cable Details

The USB cable should have an "A" plug at one end (for the computer) and a "B" plug at the other: no sockets. Any other arrangement doesn't conform to the standard. The cable comprises four wires: two carry your signal data and two supply voltage. The bus can operate at two different speeds, depending on the attached device. The device itself tells the bus what its speed is through the voltage cables. The cable should not be longer than 5 metres for fast devices, or 3 metres for slow devices. However, you can use up to 5 USB hubs to connect cables, giving a maximum distance of 30 m.


Microlink USB Options

For an overview of the Microlink units see our USB products page.


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