The need for clean, continuous power for modern laboratory instrumentation is vital to the accuracy of analysis tests and results.
by Paul Newman, Dir. of Manufacturing Engineering, Falcon Electric, Irwindale, Calif., and Dave Proli, Marway Power Solutions, Santa Ana, Calif.
Equally important is the proper distribution of that power within the lab to assure power is routed correctly. Power distribution units, or PDUs, are the common point at which equipment is tied together. Assuring the right voltages, power conditioning, conversion, control, monitoring and uptime are vital for the optimum operation of sensitive analysis and instrumentation.
There are a number of important issues that must be addressed by lab professionals weeks before their new equipment arrives to assure smooth implementation. One of the most vital issues is to assure that the lab’s AC power is clean and stable to power the new equipment. There is often a common assumption that AC power coming from the wall outlet is reliable. However, once one experiences a catastrophic power event, such as the blackout of 2003, one becomes aware of the precarious nature of the power grid. Other damaging power anomalies, such as harmonics ("noise"), high voltage transients and surges, are not as obvious as blackouts, but can cause serious equipment performance and reliability problems several months later.
Moreover, while it’s a good idea to have a generator backup system as part of the power protection strategy, generators fall short of the power quality demanded by sensitive laboratory instruments. Generator systems are unable to protect against poor power quality, have unstable output frequencies and create switchover dropouts when the utility power is lost.
In order to protect equipment from these costly power problems, many equipment manufacturers specify the use of a UPS. Most site preparation guides that specify UPS installation frequently do not specify the UPS type and quality level that is required to meet their equipment’s demanding needs. The Institute of Electrical & Electronic Engineers (IEEE) defines UPS topologies in the following categories: off-line, line-interactive and dual-conversion on-line (commonly called "double-conversion"). Because of the sensitive nature of lab instruments, a double-conversion on-line UPS is the best choice, as it solves the widest spectrum of power problems. Line-interactive and off-line UPSs, while more economical, do not provide the high level of power protection and conditioning demanded by delicate lab equipment.
The difference between these UPS topologies is often not clearly understood. About 90 percent of the UPSs on the market today are actually off-line or line-interactive designs. These battery backup units are low–cost and designed to address the basic backup needs of home PCs and office computers. These types of UPSs are not appropriate for lab equipment as they leave the equipment connected directly to the power utility source until power is lost and then switch over to the inverter, creating a 10 to 20 msec dropout during the switchover. This may be acceptable for PCs, but not for sensitive equipment that needs continuous, uninterrupted power.
Veolia case study
Falcon Electric’s SG Series On-Line 3kVA UPS, as used at Veolia Environmental Services.
In order to provide its customers with timely and accurate information to comply with California’s stringent laws governing the disposal of waste byproducts by manufacturers, Veolia Environmental Services relies on its Agilent GCMS systems to provide precise information on samples sent in for analysis.
Using Veolia’s services, customers are able to properly dispose of chemical waste, the byproduct of manufacturing electronics, computer recycling, blending fuel and other toxic materials in accordance with California’s requirements. As part of this requirement, stringent tests are required in a controlled environment that has steady temperature and power. Several hours are needed in order to complete a testing run that yields the demanding results mandated by the Environmental Protection Agency (EPA). The tests are conducted at Veolia Environmental Services by a number of GCMS instruments. A GCMS draws power for both a heating element and a microprocessor-based on-board computer. For a short period of time after a test begins, the GC oven draws a very high current for the heating element. This brief power consumption presents a problem if the power is not clean or the voltage is unstable. A typical test involves 100 samples, takes 14 hours to complete and is conducted overnight.
Prior to installing on-line UPS units to power its spectrometer, Veolia would experience unexpected shutdowns even if the power fluctuated momentarily. This, in turn, would render a total loss of the test run and any scheduled runs thereafter. Since the spectrometer would assume that the power failed—even if there was a surge, spike or other brief power anomaly—the unit would go into standby mode, rendering the test run a complete loss. Since installing an on-line UPS with power monitoring software, Veolia has not lost one test because of power pollution or voltage fluctuations.
Figure 1: Signal conditioning of AC power seeks to ensure as close to a perfect sine wave in the voltage signal as possible.
When populating a lab with new equipment, sometimes the power distribution scheme is not optimal. There may be a three-phase facility power connection available, but the equipment requires multiple single phase connections. A PDU can help resolve this issue by dividing, distributing and converting the power as needed for specific equipment requirements. To this end, distributing power for today’s lab equipment takes more than a basic power distribution unit with limited functionality. The role and benefits of advanced PDUs offer a wide array of options that can reduce complexity and costs.
As previously mentioned, sophisticated computer-based analytical systems and testing instruments require clean, stable power free of noise. A clean alternate current (AC) signal has a perfectly smooth sine wave (Figure 1) when viewed on an oscilloscope. Any imperfections in this signal can adversely affect electrical equipment, causing poor performance, incorrect functionality or damage to sensitive circuitry. Even the clean power supplied by a power utility will become degraded within a facility.
Since signal problems are introduced to power lines throughout a facility’s wiring, it is beneficial to add power conditioning at points throughout a facility. An effective place to do this is at power distribution points near the end use equipment.
In addition, a PDU can help integrate the various connector styles and power configurations required by the equipment. The PDU itself can be configured to provide the appropriate mating connectors for each piece of equipment, thus avoiding the need for adapter cables. If DC power is required for some equipment, the PDU can also be configured with an internal power supply, thus eliminating the need for external power supplies. Both of these approaches help to simplify the overall system.
Depending on the installation location and available power quality, additional power conditioning may be required by the PDU. This can include transient voltage suppression through the use of a surge protection device (SPD). It can also include power line noise suppression through the use of an EMI filter. In multi-phase applications, it is helpful for the PDU to include local monitoring capability to allow efficient installation without the need for user-provided power measurement tools. A local monitor can provide input current values for each phase, providing an easy means to ensure the entire system is balanced during setup.
Whether an off-the-shelf, modified or a complete custom power design is required, today’s UPSs and PDUs offer a smarter, feature-rich and cost-effective solution. Power performance, packaging, efficiency and reliability are all key attributes to consider when choosing power systems.
The reliability of lab equipment and its test results must be absolutely assured as a lab’s credibility can be at stake. The power distribution and power protection equipment must be up to the task to provide the highest level of clean power to the connected instruments. Laboratory professionals need to assess their incoming power and how to best provide clean, uninterrupted and advanced distributed power to their equipment. Accurate tests and results demand nothing less.