Get Your Signals Straight

By Joe Feeley, Editor in Chief

A Well-Conditioned Process Signal Is Essential for Proper System Control

T'S A PRETTY SIMPLE PREMISE: Without dependable and accurate lines of data transmission, a system cannot be properly controlled. Signal conditioners often are necessary to ensure the accuracy of analog control and process signals, improve transmission accuracy and reduce the effects of EMI/RFI (electro-magnetic/radio frequency interference) that can plague voltage signals and their high-input resistances.

A signal conditioner’s main purpose is to provide isolation and signal transformation. Over the years, technology has moved from transformer isolation to solid-state isolation. This has allowed the cost of the product to be reduced dramatically without sacrificing functionality. 

That’s Harsh
Welding Services (www.weldingservices.com), Atlanta, is in the pipe welding and weld metal overlay business, and the company designs, builds and operates the remote, semi-automated welding equipment used to support its business. (See Figure 1)

FIGURE 1: ISOLATION IS BLISS

Signal conditioners allow Welding Services' automated equipment to operate in severe envionments, where applications require them to be located several hundred feet away from the controller. This galvanically isolates the signal from the controller and provides a way to scale different input signal levels to a common, noise-resistant standard. (Source: Welding Services)

"In addition, the welding manipulators all are located inside large boilers with operators controlling the machines from inside the boiler,” says James Belcher, EE product manager for Welding Services. “The manipulators are mounted to the walls inside the boiler on large tracks. The cabling for the manipulators is routed out through one or more 18-in. manways. With the large amounts of noise generated by the welding process with our machines, and the long runs from the welding manipulator and the controller, we use signal conditioners to convert analog voltages from potentiometers and sensors to current loops. Not only does this galvanically isolate the signal from the controller, but it also provides a way to scale different input signal levels to a common, noise-resistant standard.”

For signal conditioning, Belcher requires wide bandwidth, high-speed signal conditioners. “We use signal conditioning specifically for position measurement, voltage measurement, isolation and noise immunity, all of which are very common machine design applications,” he adds.

In general, argues Dennis Fairfield, product manager at AutomationDirect (www.automationdirect.com), “data/signal transmission is the most important part of a control system.”

In addition, signal conditioners are needed to ensure that accuracy, transmission, and signal types are compatible with the rest of the control system. “The typical tasks a signal conditioner performs are conversion, isolation, amplification, filtering and linearization in the case of temperature sensor signals,” says Davis Mathews, product manager of wireless devices and signal conditioning products at Phoenix Contact (www.phoenixcon.com).

Signal Conditioning Evolves
“There are more choices today for signal conditioning and signal processing solutions for sensor network data transmission and collection,” says Donald Lupo, director of marketing & sales, process products, for Acromag (www.acromag.com). “Key differences are being made in space and cost saving designs with multi-channel instruments and universal power supply options for global applications.”

In most cases, the smaller the size of the I/O, the higher the value for the customer. Basically, more information is packed into less space. This should translate into cost savings for customers and the ability to make better use of their plant floor.

Signal conditioners have evolved from resistor-based designs that were housed in octal socket housings, to analog precision resistor designs in industrial housings, and now on to highly integrated microprocessor designs that fit in 6 mm-wide housings. “The industry is moving towards decentralized control of process signals and highly efficient compact and space-saving solutions. Peripheral devices, such as signal conditioners, should follow this trend and allow users to install remote control systems in remote locations,” says Mathews.