Effective Protection against Faults by Using Signal Conditioners

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Pepperl+Fuchs SE

Tough Demands Placed on Reliable Signal Conditioners

The signal conditioner market is highly competitive. As a result, competition over the most economical solution can come at the expense of product quality. Often, the end customer recognizes this fact too late. A number of physical effects set limits on signal conditioner performance.

• The premature aging of electrolytic capacitors at high ambient temperatures determines the temperature range in which signal conditioners can be used continuously.

• The self-heating of the entire circuit has an effect on the permissible temperature range, as well as on the switch cabinet cooling requirements

• The use of conventional trimming potentiometers may lead to time–dependent drift and calibration deviations due to manual calibration.

• Finally, the quality of the galvanic isolation determines the degree to which faults are intercepted by the signal conditioner, and thus the degree to which people and equipment can be protected.

The SC-System — Combining the Most Powerful Characteristics

The SC-System is a product line developed by Pepperl+Fuchs that combines the most powerful characteristics of comparable products in one device family. Benefits for operations include higher plant availability, greater temperature stability, and improved signal transmission quality. In addition, in the event of a fault, people and equipment are guaranteed maximum protection. In terms of switch cabinet planning, the intelligent design of the SC-System means an effective use of the available space and low cooling costs.

This breakthrough in quality has been achieved through measures that address both functional requirements and circuitry-related challenges:

• Fully automated laser trimming of fixed resistors provides the best calibration results.

• Electrolytic capacitors can dry out due to heat. In the SC-System, alternative circuit concepts are applied so that the signal conditioners can be operated at an ambient temperature of up to 70 °C.

• The low-power design, which ensures low self-heating, contributes to the wide temperature range in which the products can be operated.

• The availability of a process facility is also influenced by the probability of faults occurring, and thus by the extent to which the signal conditioner can intercept such events. The SC-System uses high-quality 3-way isolation between input, output, and supply which withstands a working voltage of up to 300 V and a test voltage up to 2.5 KV.

• Effective use of switch cabinet space when using the SC-System is achieved with a compact design: The housings, which are just 6 mm wide, reduce the space requirements of the signal conditioner modules to a minimum. The housing height is so low that the modules fit between the narrow-seated cable channels.

The SC-System signal conditioners are available in several versions with different functions: Transmitter power supplies transfer the 4 … 20 mA signals from connected signal converters and simultaneously provide the supply voltage. They are also available as Smart devices which, in addition to the analog signal, can transmit multiple Hart variables.

The portfolio includes transmitter power supplies with a signal splitter function. Temperature converters, loop-powered passive isolators, and universal isolated switch amplifiers for bipolar signals are also part of the new SC-System portfolio.

Summary: Measures taken by the process controller can make an important contribution to preventing faults and optimizing operations. In particular, interference-prone transmission paths for measurement and control signals can be effectively protected by using signal conditioners. This prevents malfunctions as long as the quality of the products meet the typical requirements of the application.

* The author is Interface Technology Product Marketing Manager, Process Automation division, Pepperl+Fuchs GmbH, Mannheim, Germany.

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