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Decoding field service reports: Reading between the lines

As we detailed in our last blog, the field service report (FSR) is one of the most valuable documents in the life of your uninterruptible power system (UPS).

Now that you are aware of the importance of this preventive maintenance (PM) service summary, we want to help you recognize and understand its most critical aspects.

The FSR will detail any deficiencies detected during the PM visit as well as list every measurement taken, including input, output and bypass voltages.

The report also notes battery characteristics such as volts and current, summarizes capacitor health, and details the inspection of a UPS’s components, electrical connections and user interface. Here is your cheat sheet for reading between the lines:

  1. Job description — This will detail the exact work completed by the technician.
  2. Job solution — Here you will find detail on the corrective actions taken during a remedial visit, or any findings that were uncovered during a preventive maintenance visit.
  3. Summary — This section will include information specific to the individual equipment that was serviced.
  4. Battery date code — This area notes the manufacturing date of the batteries — an important aspect since all batteries have a fixed life expectancy that can vary based on make, model and chemistry. The date code can be helpful for forecasting purposes. For instance, if your batteries have a five-year life expectancy, the date code is a reminder to budget for replacement at the three- to four-year mark.
  5. Status column — Review this area to determine if the UPS requires additional attention post-service call.
  6. Warnings /Failures — Pay close attention to:
  • Resistance Warning, which indicates the battery internal resistance is near failure.
  • Resistance Failure, which occurs when the battery’s internal resistance exceeds operational limits, meaning it should be replaced immediately.
  • Voltage Failure, which indicates that the battery voltage has fallen below acceptable range and needs to be replaced.
  • Date fail, which occurs when batteries have aged beyond their recommended useful life and should be replaced immediately.
  • Date Marginal, which indicates batteries that are nearing the end of useful life.
  1. Critical measurements — The readings taken during an initial PM or after a battery installation provide a baseline that can be used as a point of reference for future readings. The most important parameters to keep an eye on include:
  • Input voltage readings, which will fluctuate over time but as a general rule, should stay fairly constant.
  • Input current readings will rise as load is added and fall as load is removed. These readings should remain fairly consistent between each of the phases in three-phase systems, so a major input current imbalance could indicate a problem.
  • Input frequency should stay at or very near 60Hz. A number significantly below or above could indicate a utility or generator problem.
  • Output voltage should remain fairly constant, although it isn’t unusual to see minor fluctuations over time.
  • Output current will increase and decrease with the load. On three-phase systems, the loading on each phase should be balanced.
  • DC Voltage may fluctuate depending on the type of system.
  • AC Ripple and AC Current may start to increase as the DC capacitors begin to age, so this measurement should be monitored over time.
  • Ambient temperature should remain below 80 degrees, as any increase can be detrimental to the equipment and can result in damage.
  • Battery voltages and resistance readings will change over time, with the resistance usually increasing and the voltage decreasing as the batteries age. A premature failure will likely be indicated by a marked increase in resistance and potentially, but not always, by a decrease in voltage.
  • Battery temperature should remain within 20 degrees of ambient temperature as a general rule. Specifics on battery operating temperature can usually be found in the battery manufacturer’s documentation.
  • Specific gravity ranges should remain within the manufacturer’s recommended specifications, which are usually found on the battery data sheet.
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