power to the loop
Figure 1. Otek's new LPD series loop-powered display is 100% DCS/SCADA/Ethernet-compatible.Fest says these features eliminate the need for finger tapping on that analog meter to decide whether that meter needle is dead (stuck) or that the signal is absent. "Now the operators can't ignore the meter, as probably happened in Fukushima, Chernobyl or Three Mile Island," Fest says. "Or as a cause in the Carnival Triumph cruise ship fiasco or in so many airplane accidents that have been blamed on operator error."
How does it work? The LPD uses less than 12 mW@4 mA (<60 mW@20 mA) to run its ASIC processor and high-efficiency bicolor display and isolated serial interface, Fest says, adding that it requires only about 3 V burden on the loop, compared to about 1 V of the analog counterpart. "The alarm ‘after the fact,' or the dead loop, is handled by a unique energy storage technique used by the PLD to store power when the loop is operating normally, which is after about 30 seconds. And, if and when the loop fails shorted or open, that energy is used to flash its display, and transmit the distress message to supervisory equipment for about 20 seconds before going dark."
Otek is also expanding the LPD series with the addition of the loop-powered controller (LPC) series of bargraphs, and will include isolated retransmission (4-20 mA out), isolated alarms (four), relays and PoE. "While the LPC will require external power for the outputs, it will maintain the loop-powered features of the LPD," Fest explains.
Fest also stresses that no rewiring is required. "This is considered a very important feature by control room managers," he explains. "Since the new technology is a 100% drop-in replacement for analog meters (only two wires), there is no need to reengineer power or signal lines, as is required by conventional digital meters. And, if you want to integrate the LPD with DCS/SCADA, the serial I/O is already there. Just connect the LPD in parallel with the analog meter and disconnect the old."
Otek owns several patents on powerless technology. "The next variation to be released will be the SPD/SPC Series of signal-powered display/controllers," Fest says. "This series will use less than 50 mW of an ac signal to power the display, rather than use the loop power."
For more information call 520-748-7900, email [email protected] or browse to www.otekcorp.com.