Panel Meters Take on New Jobs

Panel Meters Also Can Be Used in Conjunction With PLCs as Part of a Redundant System to Help Ensure the Safety of Production Equipment and Operators

Jim MontagueBy Jim Montague, Executive Editor

What have panel meters done for you lately? Well, as their power and functions increase and as machine operators assume more responsibility for running them, the question may soon be, “Is there anything panel meters can’t do?” As a result, more users want to know exactly what the devices are capable of and whether they might do some of the jobs of a small PLC/HMI combination.

Panel meters are increasing their available output capabilities, says Vince Leonardi, group technical leader/applications engineer for Omega Engineering. “Our DP41B series is available with four open collectors and four relay outputs, plus Ethernet connectivity,” he says. “While not capable of doing mathematical computations, the meter is flexible for more event/alarm situations and can be viewed over a network.”

As always, cost remains an issue. “By the time you add smart functionality and communication boards, panel meters start to approach the cost of micro and pico PLCs and small HMIs,” says David Kaley, product marketing manager at Omron Electronics. “Even if only one or two critical parameters are monitored, HMIs can combine external switches and a more informative display in one package. This brings down the installed cost and increases system reliability by involving fewer separate components.”

Kaley says Omron’s panel meters can change display colors to accentuate a status change, “but this function isn’t widely embraced and is seldom used,” he adds. From a machine lifecycle view, smaller PLCs allow machine designers and programmers to worry about one programming structure instead of multiple structures and software for various panel devices, adds Kaley.

“When we look at the market and users’ preferences, we see two contradictory trends,” says Avner Barak, technical business development manager at Unitronics. “On one hand, customers like the ability to separate the system into object-oriented components, allowing each part to do its own task. On the other hand, combo products are becoming more popular, providing a less expensive solution to the entire system’s requirements.” PLCs are acquiring meter-like capabilities and can replace them in certain systems, adds Barak.

It’s unlikely that panel meters will replace PLCs and HMIs anytime soon, but meters can now be used not only to display information but also as a convenient means for local control and as a component in redundant backup systems. Leonardi believes the trend in panel meters isn’t so much moving toward PLC capability, but blending in controller functions to become more universal. “In the past, you might have had to purchase three devices—one to measure a process, another to control the process and a third as a safety limit device. Now users can program one unit to be a panel meter with alarms, a PID controller with auto-tune or a safety-limit controller.”

So, how much real control can we get from a panel meter today? “On/off control, PID and one ramp-and-soak program are all possible with our iSeries,” says Leonardi. Auto-tuning, he adds, is already standard.

“Panel meters can be used for simple machine control, allowing maintenance staff to make real-time adjustments in response to changing production conditions reflected in panel meter readings,” says Jeff Thornton, product manager at Red Lion Controls. “This ensures that production remains as efficient as possible and eliminates the time and costs spent on enlisting a programming engineer’s assistance to provide PLC support.”

Panel meters also can be used in conjunction with PLCs as part of a redundant system to help ensure the safety of production equipment and operators. For example, says Thornton, if a PLC used to control conveyor speed in an assembly application fails, a panel meter can be programmed to deliver a local readout of conveyor speed and cut off power to the conveyor if it exceeds the maximum speed allowed.

There will be a few niche applications where a smart panel meter makes sense, adds Kaley. “But, we think those spaces are too few to justify further development of panel meters with integrated logic.” Too true for now. but maybe not for long.

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  • <p>In 2008, DPMs were experiencing a technological rebirth. They began to offer more than just a display. Take for example the HI-Q Series from OTEK. These digital bar-meters were introduced in 1992. The externally powered models included relays, analog output, isolated serial I/O, mathematical functions, polynomials and X-Y tables. These features were indispensible for MMI compliance. A HI-Q unit was also equipped with an automatic-tri-color bargraph for HMI compatibility. This became available in 1998! Now in 2015, the same company (OTEK Corporation) offers the NTM and UPM series. Both series feature a 99% power savings over the HI-Q series and other manufactures models. The NTM and UPM can be loop, AC/DC signal or externally powered. Externally powered units include all the features of their renowned HI-Q series (relays, analog out, Ethernet (PoE), Math. Functions and Polynomials). The loop and signal powered versions also feature their patented signal failure detection and alarming. Using stored energy, the NTM and UPM series can transmit serially to supervisory equipment a record of the failure and for approximately 20 seconds display a message on the unit that reads “INPUT FAIL,” eliminating future Fukushima-like disasters. The UPM and NTM series comes in 1-6 channels challenging the PLC niche in PAC market. Imagine replacing an analog meter with a digital, without supplying power to it!</p> <p>For more information visit www.otekcorp.com or contact Dr. Otto Fest at 520-748-7900 or opfest@otekcorp.com. </p>

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