Test & Measurement

On the other hand, many data acquisition boards have only 12- to 18-bit resolution. This results in limited measurement precision, typically less than 41/2-digit resolution. In addition, a large number of PCs are required for the local monitoring points. This drives up system costs and creates a major maintenance burden.

There are GPIB (General Purpose Interface Bus) based instruments that have higher speed and measurement precision. However, GPIB connections are limited to a 20-m cable distance, and the data transfer rate is limited to about 1MB/s. Hence, GPIB based instruments are not suitable.

To improve magnet monitoring and beam quality, high-resolution Etherne tbased measurement systems can be installed. These systems combine high-precision digital multimeter (DMM) functions with a solid-state multiplexer for high-speed multichannel measurements of magnet voltages. These instruments allow measurement resolutions as high as 6 1/ 2 digits, and their multiplexer modules can be configured for up to 40 differential channels. The Ethernet interface allows each instrument to be placed up to 200 meters away from the central control room. (With Ethernet hubs, the distance is virtually unlimited.) On a dedicated network, data transfer rates can be up to 100Mb/s.

Multiple DMM/MUX instruments are located around the storage ring and connected to a central workstation’s 100BaseT network via TCP/IP Ethernet protocol. Each instrument and PC network interface card has a unique TCP/IP address. Operators can communicate with the instruments via Internet Explorer by entering the TCP/IP address in the browser’s URL line. The instruments have a built-in Web page that simplifies setup, troubleshooting, and data collection.

By combining the long-distance, multi-box control capability of Ethernet with the instrument configuration described above, a more economical, nearreal-time monitoring solution is created. It requires fewer PCs than earlier solutions, while providing superior measurement precision and control.

This article was written by Mark Cejer, Business Manager for Keithley Instruments. The full text of this article is available online at www.keithley.com/servlet/Data?id=15068.

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