other sensors. Right now in the process industries, the only limitation to greater use is a shortage of devices, other than I/O modules, that are certified for safety. “In the last five years, a number of device manufacturers have been investing the money necessary to get their devices certified,” says Fialkowski.

Diagnostics bonus

He and others think that, besides streamlining installation and upkeep, the biggest advantage of consolidating safety and control networks will be the range of diagnostics that it makes available. “Signals from hard-wired sensors simply say whether it’s safe or unsafe,” explains Arens at Bosch Rexroth. Putting the devices on a network, on the other hand, gives users the ability to monitor the systems, troubleshoot problems, and perform routine diagnostics without having to send a technician to pull and check each component manually.

Some of these diagnostics can be continuous, and others can be periodic, according to a preprogrammed maintenance schedule. A transmitter with a temperature element in it, for example, will report temperature continuously. In other instances, a controller could check the calibration of sensors automatically. It could tell a transmitter to hold its signal while going from zero to full scale and then to return to its original status. “This would tell you whether it drifted,” says Jeremy Bryant, a networking specialist at Siemens.

He notes that, labor notwithstanding, speed is probably the chief advantage of this kind of calibration check. “When you take a transmitter off line, you’re basically running blind for that period of time,” he says. “Most users want to minimize that.” Because the calibration checks allowed by the consolidation of networks are so fast, users could run them much more frequently in much less time.