affiliated with the authors of this page or responsible for its content.
Operational Mode TP ENERGY STAR
®
Qualified Imaging Equipment
Test Procedure
Operational Mode Measurement
June 28, 2004
This document provides an example of an ENERGY STAR operational mode test procedure. For
simplicity, printers and fax machines are used as an example.
Outlined below are the ambient test conditions that should be established when performing the power
measurement. These are necessary in order to ensure that outside factors do not affect the test results,
and that test results can be reproduced later. A description of the specifications for testing equipment, as
well as a discussion of testing issues, follow on the succeeding pages.
Test Conditions
Line
Impedance:
Total Harmonic Distortion:
(Voltage)
Input AC Voltage:
1
<
0.25
ohm
< 5%
115 VAC RMS +/- 5V RMS
4
Input AC Frequency:
60 Hz +/- 3 Hz
Ambient Temperature:
25 deg. C +/- 3 deg. C
Test Method
Printer and fax machine manufacturers should measure and report the average power consumption of
their printer and fax machine products when in the Sleep Mode. This should be done by evaluating the
printer or fax machine over a time period sufficiently long to include typical variations or surges in power
(e.g., any cycling of the fuser). The recommended approach is to utilize a watt-hour meter, and measure
the energy consumption in the Sleep Mode of the printer or fax machine over 1 hour. This will allow
manufacturers to capture any variations in power usage that occur during the Sleep Mode. Dividing the
measured energy consumption by the time period over which it is measured will produce average Watts.
While this approach will provide the most accurate results, it is not essential to follow this for printers and
fax machines whose idle-mode power consumption does not vary (e.g., dot matrix printers, inkjet type
printers and fax machines, and laser printers and fax machines where the fuser is turned off during idle
mode). For printers and fax machines with constant idle-mode power consumption, manufacturers may
choose to utilize a high quality watt meter and take several measurements of instantaneous power.
If products will be sold in Europe or Asia, testing should also be performed at the appropriate machine-
rated voltage and frequency. For example, products destined for European markets might be tested at
230 V and 50 Hz. The logo should not be displayed on products shipped to Europe or Asia if the
equipment does not meet the power requirements of the Program at the local voltage and current
conditions.
1 Testing Equipment
The goal is to accurately measure the TRUE power consumption
2
of the printer or fax machine. This
necessitates the use of a True RMS Watt Meter or Watt-Hour Meter. There are many watt meters and
watt-hour meters to choose from, but manufacturers will need to exercise care in selecting an appropriate
model. The following factors should be considered when purchasing a meter and setting up the actual
test.
Crest Factor
A previous version of EPA's testing procedure included a requirement that manufacturers utilize a meter
with a crest factor greater than eight. As many Partners pointed out, this is not a useful or relevant
requirement. The following paragraphs are meant to discuss the issues relating to crest factor and to
clarify the intent of the initial statement. Unfortunately, EPA cannot provide a specific equipment
requirement because testing is as much art as it is science. Manufacturers and testers will have to
exercise judgment, and draw on people well versed in testing issues, to select an appropriate meter.
It is important to understand that electronic equipment such as printers and fax machines typically draw
current in a waveform different from typical sinusoidal current.
3
While virtually any meter can measure a
standard current waveform, it is more difficult to select a meter when irregular current waveforms are
involved.
It is critical that the meter selected be capable of reading the current drawn by the printer or fax machine
without causing internal peak distortion (i.e., clipping off the top of the current wave). This requires a
review of the meter's crest factor,
4
and of the current ranges available on the meter. Better meters will
have higher crest factors, and more choices of current ranges. When preparing the test, the first step
should be to determine the peak current (amps) associated with the printer or fax machine being
measured. This can be accomplished using an oscilloscope. A current range must be selected that will
enable the meter to register the peak current. Specifically, the full scale value of the current range
selected multiplied by the crest factor of the meter (for current) must be greater than the peak current
reading from the oscilloscope. For example, if a meter has a crest factor of 4, and the current range is
set on 3 amps, the meter can register current spikes of up to 12 amps. If the measured peak current is
only 6 amps, the meter would be satisfactory. However, if the current range is set too high in order to
register peak current, then it may lose accuracy in measuring the non-peak current. Therefore, some
delicate balancing is necessary. Again, with more current range choices and higher crest factors you will
get better results.
2
True power is defined as (volts)x(amps)x(power factor), and is typically reported as Watts. Apparent
Power is defined as (volts)x(amps) and is usually expressed in terms of VA or volt-amps. The power
factor for equipment with switching power supplies is always less than 1.0, so true power is always less
than apparent power.
3
The crest factor for a sinusoidal 60 Hz current waveform is always 1.4. The crest factor for a current
waveform associated with equipment containing a switching power supply will always be greater than 1.4
(though typically no higher than eight). The crest factor of a current waveform is defined as the ratio of
the peak current (amps) to the RMS current (amps).
4
The crest factor of a watt meter is often provided for both current and voltage. For current it is the ratio
of the peak current to the RMS current in a specific current range. When only one crest factor is given, it
is usually for current. An average True RMS Watt meter has a crest factor in the range of 2:1 to 6:1. Frequency Response
Another issue to consider when selecting a watt meter is the frequency response rating of the meter.
Electronic equipment that contains switching power supplies causes harmonics (odd harmonics typically
up to the 21st). These harmonics must be accounted for in power measurement, or the Wattage
consumption will be inaccurate. Accordingly, EPA recommends that manufacturers purchase meters that
have a frequency response of at least 3 kHz. This will account for harmonics up to the 50th, and is
recommended by IEC 555.
Resolution
When testing printers and fax machines whose power consumption is close to the ENERGY STAR
requirements, manufacturers will probably want a meter than can provide resolution of 0.1 W.
Accuracy
Another feature to consider is the resulting accuracy you will be able to achieve. Catalogues and
specification sheets for watt meters typically provide information on the accuracy of power readings that
can be achieved at different range settings. If you are measuring a product that is very close to the
various watt ceilings noted in Tables 1 through 8, you will need to set up a test that will provide greater
accuracy. For example, if the resulting accuracy for your watt-meter at the test settings is + 0.5 W, then
with a measured power consumption of < 29.5 W you can be fairly sure that your printer or fax machine is
compliant.
Calibration
Meters should be calibrated every year to maintain their accuracy.