Variable Measurements Evolve

Pressure and Other Air Signals Aren't New, but What's Evolving Is Higher Resolution for Converting 0-10 V Analog Signals into 10-bit or 16-bit Digital

Jim MontagueBy Jim Montague, Executive Editor

Temperature, pressure, weight and flow variables have been elements in discrete manufacturing operations pretty much forever. However, their presence usually was segregated within the equipment they served. More recently, thanks largely to software and PC-based control's continuing emergence, these boundaries have been blurring. Computers don't care whether an application is process or discrete; they just want some digital data to chew on.

Pepperl+Fuchs reports its Termex panel has long been used in Europe's flavoring industry for dosing applications ranging from micrograms to kilograms, and it can bring in data from three scales and coordinate and control their performance via one HMI. However, the trend now is toward PC-based recipe management via Ethernet to coordinate multiple signals and processes, according to Lou Szabo, business development manager for Pepperl+Fuchs' ( systems solution division.

"We used to have production lines organized in separate islands and sections, and measurements and resulting orders were transferred by hand on paper. Now, lines are far more integrated, the sections are more dependent on each other, and they communicate via Ethernet," says Szabo. "This means large control and automation suppliers are helping machine builders with batch recipe management because, for example, a builder's pharmaceutical end user wants a machine that makes its pill and the package to put it in."

Pressure and other air signals aren't new, but what's evolving is higher resolution for converting 0-10 V analog signals into 10-bit or 16-bit digital.

Paul Ruland, Siemens Energy and Automation's ( product marketing manager for discrete automation, adds that process variable measurements in machine building also show up in devices moving air-related signals, such as in pneumatics, compressors and vacuum. "Of course, we're also seeing I/O points that need to change analog signals to digital, and use of switch-related sensors is becoming more dominant," says Ruland. "Pressure and other air signals aren't new technologies, but what's evolving lately is higher resolution for converting 0-10 V analog signals into 10-bit or 16-bit digital signals for more precise and useful measurements that can be better evaluated in a PLC."

Siemens also is seeing better communication by using fieldbuses such as Profibus that can bring in and read many analog or process signals such as speed references, encoder signals, drives and servo signals, or maybe a heat reference for one of those drives, says Ruland. "For example, Siemens can install a small ET200 distributed I/O module, bring in an individual analog pressure, temperature or weigh scale signal via Profibus or Profinet, and that weigh scale will show up as just another node on the network," he says. 

"As users move from straight, time-based or run-to-failure maintenance, they need information on asset condition, so they can integrate that physical, process data into a condition-monitoring platform, and improve performance," says Scott Breeding, product line leader for Bently Nevada, a division of GE Energy ( "This is what gives users an indication that a bearing might be running hot,  before they can see any signs of wear or damage. Process measurement data allows users to focus more closely on the ‘bad actors' in their applications."

Also, though vibration detection and analysis is a bread-and-butter machine-health monitoring method, some developers believe ultrasonic monitoring might be even more useful. Based on military and aerospace monitoring methods, stress wave analysis (SWAN) technology from Swantech ( reportedly can detect even earlier when a machine is starting to demonstrate symptoms that will lead to failure. "Ultrasonic technology provides the earliest detection of machine problems by detecting the unique sounds made by friction, impact events and minor surface damage," says Ralph Genesi, Swantech's president and CEO. "Traditional machine health was based on vibration, but this is too late because damage may already have occurred. Ultrasonic detection gives users more time to plan maintenance and a response and lets users decided if they need to shut down now or if they can safely run their planned quota."