Product Focus: Loop-Powered Instruments Offer Alternative to Analog Meters

With infinite resolution and lossless quality over any distance, the 4-20 mA current loop has dominated the control industry in its simplicity and reliability. Analog current meters are limited by this simplicity, however, providing the user with little more than a failure-prone generalization of a process' status. The Computer Age has ushered in a wave of panel instrumentation that offers higher precision, better visibility, increased functionality, and continued manufacturer support.

New passive, loop-powered digital devices coming into the market are designed to operate using the existing 4-20 mA current loop. These instruments rely on the power generated by the current loop to operate and can provide the high degree of precision demanded to optimize a process and remain competitive in today's market.

These meters can be a drop-in replacement for analog instrumentation, but until recently have tended to carry a heavy loop burden and have little more functionality than a standard analog meter.

Fortunately, digital technology is always reaching new milestones. Handheld technologies have created a demand for ultra-low-power microprocessors. LEDs are made continually better and brighter. Integrated circuits are designed to run faster and at lower voltages. These advances have reached a point where robust digital instrumentation can work interchangeably with old analog meters, powered simply by the current loop.

Brighter, color-changing displays, several digits of precision and DCS/SCADA interfacing are just some of the benefits of a new digital control panel.

One company offering digital replacement instruments is OTEK Corp. The company offers a variety of bar graphs and digital display meters with 4-20 mA input and output options that have been specifically designed to replace obsolete analog/digital indicators, offering the same form, fit and function. Display options include LCD or LED lights.

The company offers a Replacement Guide which lists analog 4-20 mA meters and bargraphs and their direct digital replacements.

Instruments can be 100 percent loop powered (4-20 or 10-50 mA), and place only a 3v burden on the loop (< 16 mW @ 4 mA, 60 mW @ 20 mA). The instruments offer automatic loop failure detection (open or shorted) and data transmission with a date and time stamp. Communication options include USB or RS485 isolated Serial I/O for DCS/SCADA/PLC/Intranet. The company's Loop Powered Controller (LPC) series offers isolated 4-20 mA retransmission and four opto-isolated open collector transistors (OCT) or 10 Amp relays. These options are not powered by the loop.

For more information on OTEK Corp. and its products, visit www.otekcorp.com.

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