Unsung but Indispensable

Control systems come in all sizes and levels of sophistication. From the simplest relay-logic circuit for a dedicated semiautomatic assembly machine to large DCS-based systems of sprawling process plants, they all have something in common—they cannot simply be plugged into a wall socket to power them up.

By Dick Johnson May 1, 2004

Click here to view the complete research results from the April 2004 Electric Servo Motors Product Focus Study in the Resouce Center.

Control systems come in all sizes and levels of sophistication. From the simplest relay-logic circuit for a dedicated semiautomatic assembly machine to large DCS-based systems of sprawling process plants, they all have something in common—they cannot simply be plugged into a wall socket to power them up.

Containing a wide variety of computer electronics, instrumentation, sensors, and actuators, control systems rarely run on a ‘diet’ of unregulated ac power. In some cases, supplied power matches power quality requirements of the load, and simply converting the form of energy supplied from ac to dc may be all that is required. However, most process and instrumentation control power requirements are incompatible with inherent variations in the average industrial or utility power source. In cases like these, much more regulation is needed.

User interest in the state of power supply technology is evidenced by the response to a recent study on ac to dc power supplies conducted by Control Engineering and Reed Research Group (both divisions of Reed Business Information, www.reedbusiness.com ). The e-mail/Web-based study reports on results from 265 respondents directly involved in specifying, recommending, and/or buying ac/dc power supplies.

Although application of power supplies was universal across all industry types, some areas see more concentrated use than others. These include applications involving both continuous and batch processing (32.5%) and discrete product manufacturing (27.4%). Continuous processing only accounted for 17.5% of those polled. The ‘other’ category accounted for 10.7% of the responses—test equipment/systems were the most often mentioned area in this category. The final tally placed utilities at 8.7% and batch processing only at 3.2%.

What’s the future of features?

Given power supplies’ importance to control systems large or small, it’s no wonder that reliability (82.1%) claimed top spot in power supply features deemed ‘most important’ by the survey responders. Reliability also ranked as the number-one feature in the 2002 survey. Relative ranking of other ‘most important’ features are in the accompanying graphic.

Generally, performance features held their places when compared to the earlier survey. Ranking of features, which included such items as input voltage protection, ability to handle large power outrush, active power filtering, redundancy, and automatic power factor correction changed little from the 2002 survey. Overall, the same can be said for installation and maintenance issues with the exception of ‘meets space requirements’ category, which jumped from fifth to second place in order of importance. There seems to be real impetus for this change.

According to Bruce Desmond, product manager of power supplies and relays at Phoenix Contact, ‘Ability to save space while maintaining industrial-grade performance is among the top design criteria of today’s power supply users. One of the most important features of industrial-grade power supplies is the ability to provide full nominal output current at temperatures as high as 140

‘The need to de-rate power supplies has a very negative effect on its ultimate size. For example, a compact power supply with a nominal current rating based on 104continues.

In the informed consumer’s eye, attributes such as quality, customer service issues, and brand loyalty drive the purchasing decision. The same principle holds true for industrial users who count on a power supply to keep their control system up and running. Survey results mirror this, with very little change in attribute ranking compared to the 2002 survey.

Power quality, availablity

Product quality was chosen most often as ‘very important’ for manufacturer selection (79.8% of respondents), followed by a vailability (59.2%), price (41.4%), customer service (39.8%), Web site information (35.6%), technical assistance (31.3%), and previous experience with the manufacturer (28.7%). The final items in the ranking were the existence of a local sales representative ( 15.1%) , Web site purchasing capability (10.9%), and available training (5.2%).

Attribute rankings remained essentially the same from the previous survey, but Web site access for product information was a ‘gainer’ in the 2004 list. In a world of increasing Web usage, this is hardly unexpected. Power supply manufacturers have made good use of the Internet for disseminating product information. Brian Leeson, product manager, power supplies, at Rockwell Automation, says, ‘There are many performance characteristics for power supplies, and manufacturers provide the critical data via the Web to allow customers to make an intelligent selection for their application. Customers frequently access the comprehensive technical specifications, application notes, and CAD drawings for Allen-Bradley Bulletin 1606 Power Supplies.’

Ability to purchase from a Web site was not high on the list of survey results nor is it currently the case for customers of A-B products. This, too, is not an unexpected circumstance. Leeson continues, ‘Because our customers value the technical support and local inventory provided by our channel, they tend to conduct purchases through a sales person and not through the Internet. This provides customers with the ultimate confidence that they’re selecting the most appropriate device for their application.’ Apparently, it is still hard to beat service with a smile.

Power supply products

For more manufacturers, visit www.controleng.com/buyersguide . For system integrators go to www.controleng.com/integrators . Also visit company Web sites listed.

EXCLUSIVE: Protected power supplies

Phaseo modular dc power supplies incorporate new and advanced solid-state features such as Telemecanique’s integrated overload, shortcircuit, overvoltage, and undervoltage protection. Available in three versions—single-phase, three-phase, and ultra-compact—these supplies are regulated and switch-mode with adjustable outputs. These additions have the same ‘family’ look but have smaller, more compact enclosures and emit lower current using same voltage as the standard Phaseo units. New features include reduced weight, higher output-voltage stability, and modular format for easy installation. A wide input voltage range is accommodated without any adjustment.

Phaseo single-phase power supplies provide dc voltages necessary for equipment control circuits (100-240 V ac and 12-24 V dc). They measure 24 V dc. All three Phaseo lines deliver voltage accurate within 3%, regardless of load and supply voltage in a range of 85-264 V ac.
Schneider Electric www.squared.com .

PFC, sag immunity featured

The SDN-P family of single-phase 24 V dc DIN-rail power supplies is designed to provide reliable dc power for industrial process controls, machine tools, or other equipment exposed to harsh factory environments. Housed in a rugged, compact casing, they’re suitable for Class 1, Div. 2 hazardous locations and DeviceNet applications. They are available in 2.5-20 Amp range to fit most applications, with efficiencies up to 90% typical. SDN-P family also meets SEMI F47 Sag Immunity standards to guard against electrical disturbances of the mains, plus offers built-in power-factor correction (PFC) to reduce losses. All features are contained within a 3.26-in. wide high-density package. Other design innovations include auto select 115/230 V ac nominal input, a ‘DC OK’ signal, plus adjustable voltage.
Sola/Hevi-Duty www.solaheviduty.com .

Power-dense, modular units

ESP4 Series, a new line of mid-power modular ac/dc power supplies includes a 400-W and a 600-W chassis, offered in power-dense 2.56 x 5 x 10.63 in. packages. Five single-output, and two dual-output modules can be configured in series or parallel to provide up to eight outputs from 1.45 to 58 V dc. They also feature wide input range (88-264 V ac) and are compliant to EN61000-3-2 (PFC) and Class B conducted emissions. The devices also meet EMC requirements of EN61000-4-2, -3, -4, -5, -6 and -11. Safety agency approvals include UL and cUL. Standard options include Input Power Fail, Global Enable or Inhibit, and a bias output supply. Individual output modules have a Power Good signal, Output Inhibit, and Remote Adjust feature.
Power-One www.power-one.com

Programmable dc power supply

The newest dc power supply from Acopian can be programmed through its output voltage ranges with a 0-10 V input from a D/A converter of a PLC. Output ranges from 0-6 to 0-100 V dc are available with currents up to 30 Amp. Most modular models can be mounted on a DIN rail or a vertical panel. Models that mount in 19-in. racks have metering as an option. Other control voltage ranges are available. All are covered by a five-year warranty.
Acopian www.acopian.com

Switched-mode for low voltage control

To meet increased safety and reliability demands in low-voltage applications, Rockwell Automation has introduced a line of general-purpose switched-mode power supplies. Allen-Bradley Bulletin 1606 low-voltage power supplies accept wide ranges of ac and dc input voltages and meet worldwide single-phase and three-phase requirements. Comprised of two families—1606-XL (standard) and 1606-XLP (compact)—A-B Bulletin 1606 features start-up and overload response that provide smooth electrical load distribution. All units feature an overload design that delivers up to 80% higher continuous current (over maximum device rating), at a reduced voltage with no negative thermal effects. This eliminates the need for designers to oversize the power supply and minimizes potential overload damage.
Rockwell Automation www.rockwellautomation.com .

Predictive maintenance = cost savings

S8VS switch-mode power supplies feature a 3-digit, 7-segment LED to display a lifetime monitor and a run-time monitor. Lifetime monitor shows an estimate of the power supply’s remaining service life in years, thus helping to eliminate downtime. Run-time monitor displays how long a load has been operating, so that the networked power supply can indicate to another device to take corrective action as part of a predictive maintenance program. Additionally, S8VS features overload and over-voltage protection. These power supplies are available in 60-, 90-, 120-, and 240-W versions. The 60-W version reportedly offers the industry’s smallest width—40 mm. Prices start at $99.
Omron Electronics www.info.omron.com

Hazardous location power supplies

Quint G2 family of power supplies is now approved for use in the Class I, Div. 2 hazardous areas. The power supplies provide universal 24 V power with output currents of 2.5, 5, 10, 20, 30 and 40 A and accommodate a wide input voltage range for both ac and dc applications. Output currents are available with a regulated and adjustable output voltage of 22.5-28.5 V dc; in addition, 12 and 48 V adjustable outputs are available. G2 units are DIN-rail mountable, fully enclosed, have integral function monitoring via dual alarm outputs with LED indication, and use proprietary screw-actuated terminal blocks for ease of wiring. Class I, Div. 2 approval applies to the entire Quint G2 amperage range, while ATEX, Zone 2 approval applies to new 5 and 10 A versions. All Quint G2 power supplies are UL 60 950 and UL 508 listed.
Phoenix Contact www.phoenixcon.com

Click here to view the complete research results from the April 2004 Electric Servo Motors Product Focus Study in the Resouce Center.

Additional Online Products

Universal, modular power supply

OEMs can now offer customers a single, two-phase, 5-10 Amp power supply from Siemens E&A that accommodates voltages in 193 countries. Sitop modular 24-V power supply is the first 5 and 10 Amp unit designed for most common single-phase and three-phase networks worldwide in a single unit. Sitop DIN-rail mounted and compact power supplies are also available in 20 and 40 A versions and can be used for voltage ranges from 85-132/176-264 V ac and also 320-550 V ac. Standard features include two short-circuit shutdown choices and three operational status indicators. A power boost function delivers up to 300% rated output current to handle high inrush loads. It also offers a load-sharing function, adjustable output voltage up to 28.8 V dc, and a robust IP20 metal housing. In addition to its complete product range of 24 V dc units—from 0.5 to 40 A—Siemens also offers power supplies for 5, 12, 15, and 48 V.
Siemens Energy & Automation

Miniature, open-frame switching supplies

OFM 40/60 Series ultra-miniature, open-frame switching power supplies feature small size (2 x 4 x 1.2 in.), full safety approvals, and low cost per watt. All models accept universal input from 85-265 V ac, with 27 models available to provide single (40 and 60 W), dual and triple (40 W only) outputs of 3.3 to 48 V dc. The devices have power densities greater than 6 W/inng. All models contain over-voltage and short circuit protection circuitry and internal input filtering. All are approved to EN60950/UL1950 safety specifications.

Cost-effective power supplies

The 787 Series switch mode power supplies are said to provide a broad range of highly reliable, cost-effective dc power sources for any industrial control application. Its metal-clad housing offers shock-proof, industrial strength, and compact DIN-rail-mount design. They are available in single- or three-phase versions with input voltages of 90-264 or 325-550 V ac; output voltages of 12 or 24 V dc; current ratings of 1.3, 2, 2.5, 4, 8, 10, or 20 Amp; and power ratings up to 480 W. Other features include high efficiency, over-voltage/short-circuit protection, surge protection, and inrush current limiting via NTC resistor to ensure operational reliability. They are UL and cUL approved to the 508 and 1950 standards (other worldwide approvals available).

Regulated output for sensitive loads

The PSP line of dc power supplies is available in 12 or 24 V dc versions, with ratings of 1-5 A at 24 V dc and 4 or 8 A at 12 V dc. Features include DIN-rail mounting, low ripple and noise, plug-in screw terminals or cage clamp terminals, and a compact plastic case. The line offers regulated output voltage for sensitive loads in industrial environments, as well as constant-current short-circuit protection to protect components from direct shorts and device failures. Most models meet NEC class 2 requirements and all are UL/c UL 508 listed, UL/c UL60950 recognized. Prices start at $55.

Small is beautiful in power supplies

Puls has developed what is said to be the market’s smallest 72 W Class 2 DIN-rail power supply. The ML70.100, a product of its developer’s DIN-rail mounted, switched-mode power supply technology, measures 45-mm wide and conforms to UL1310 specification for low-power sources. In addition to its small size, ML70.100 Class 2 power supply achieves efficiencies of 89% and uses double locking spring clamp technology so that no tools for installation are required. ML70.100 is designed to meet all worldwide standards including UL, EN, CSA, and CB Scheme.
Puls US

High-integrity power supply

Elcon high-integrity power supply is a 15 Amp, 24 V dc system specifically designed for highly efficient, reliable operation in mission-critical applications. Its modular design provides N+1 redundancy for uninterrupted system power, hot swapping for live replacement, and LED and alarm outputs for audio-visual status indication and diagnostic evaluation. The power module plugs directly into a 3- or 6-position chassis for maximum capacity of 45 or 90 A, respectively. Elcon modules require no internal or external cooling fans, and are adjustable from 22.5 to 28 V dc for precise voltage regulation. Input is rated for ac or dc voltage, allowing a battery backup supply to be used. Also, an automatic load-sharing feature eliminates load imbalances often associated with ordinary linear power supplies.

Compact DIN-rail power supply
ASI has introduced a new line of compact DIN-rail mounted, switching-power supplies. They are “universal auto-ranging,” which means that the same part can be used with either 110 or 220 V ac inputs. Additionally, they offer many new features and occupy “the least amount of space on a DIN-rail compared to alternative designs,” says the manufacturer. These primary switched power supplies, available from 5 to 480 watts, provide a clean regulated source for dc power and are fully compliant with UL, CSA, and CE safety and electrical noise requirements. The 24 V dc power supplies are available in versions ranging from 1 to 20 Amp outputs. Universal auto-ranging ac input voltages are either 90-264 V ac (single phase) or 340-480 V ac (three phase). Other 5, 12, 15, and 48 V dc versions are also available.
Automation Systems Interconnect