Wireless graphical terminals and PC-based workstations are being used with increasing frequency on plant floors. For example, Ashland Specialty Ingredients' plant in Lima, Ohio, has implemented Emerson Process Management's
Smart Wireless Mobile Worker solution to increase productivity of its techs. It consists of Wi-Fi access points and handheld, PC-based workstations linked to controls and monitors.
John Rezabek, process control specialist at Ashland (and author of Control's "On the Bus" column), explains: "We can now execute loop checks during commissioning and routine calibration checks with one person instead of a two-person team. Alarm and shutdown conditions are easily simulated during ESD testing, and our field operators can view live process displays during start-up. The mobile interface goes where operators need it and displays what's needed to complete tasks. Field operators can also monitor the process during abnormal situations such as a control valve bypass."
“We can now do loop checks during commissioning and routine calibration checks with one person, instead of with a two-person team.”
- John Rezabek
Meanwhile, ATCO Power's facility at Battle River in Alberta, Canada, uses Beamex's
MC5 multifunction documenting calibrators and CMX Professional calibration management software to calibrate, configure and troubleshoot about 600 instruments. Previously, there was lots of tubing connected to the old calibration equipment, causing difficulties, but now the MC5 calibrator uses one, integral three-way hose. "When I calibrate an RTD, I just plug in two or three leads, and the calibrator does the rest," notes Shane Haugen, an instrumentation engineering technologist at the plant. Beamex's device calibrates virtually every instrument in the plant, replacing many single-function calibrators. "Creating a single database that people can access has been one of the biggest benefits. Also, it used to be painstaking to get an individual up to speed on all of our calibration hardware and software, but MC5 and its software alleviated these issues and made calibration far easier," adds Haugen.
Many plants have simple operator interface terminals installed in the field, but want to upgrade to PC-based workstations. "Our customer, Trimax, a system integrator in California, upgraded the SCADA system at a southern California water plant," reports Bjoern Falke, product marketing manager for control systems at Phoenix Contact.
With the limited-function interface terminals, operators often had to go back to the main operations building or radio another operator to assist in looking at the SCADA computer in the operations building. "Upgrading to our Valueline industrial PCs with a 17-in. screen makes it possible to view entire SCADA screens with legible text, just as at the operations building," continues Falke.
To limit potential radio frequency (RF) interference of its wireless applications and mobile users, Emerson performs RF site surveys of areas requiring Wi-Fi coverage to determine where to put wireless access points, according to Neil Peterson, Emerson's senior manager for wireless marketing. A professional RF site survey is more sophisticated than the simple "post" commands that deliver fairly static web pages or emails via home-based hotspots, and so can still work with a weak signal. "We temporarily install Wi-Fi access points in the plant, and physically move around everywhere coverage is needed, so we can determine the signal-to-noise ratio (SNR) everywhere field workers might use a tablet or laptop. We climb stairs and walk all around the process unit, etc. Per Cisco standards, coverage areas should nominally have an SNR of 18 dB, which coincides with 18 Mbps bandwidth. This is a fairly strong signal—approximately three bars would show on your laptop icon. We do this because laptops will still connect in the presence of a weak Wi-Fi signal, but they can experience high packet loss. Control system communications are fairly sophisticated, so packet losses cause resends, which bog down communications and cause applications to not work."