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OEM FUNCTIONAL SPECIFICATION ULTRASTAR XP (DFHC) SSA MODELS 1.12/2.25 GB - 1.0" HIGH
2.2.3.1 Power Calculation Examples
Note: The following formulas assume all system ops as a 1 block read or write transfer from a random
cylinder while at nominal voltage condition.
Example 1. Calculate the mean 12 volt average current.
If we assume a case of 30 operations/second then to compute the sum of the 12 volt mean currents the
following is done.
mean
+12VDC (idle average) 0.77 amps
+12VDC (seek average) 0.0036 * 30 = 0.11 amps
TOTAL 0.88 amps
Example 2. Calculate the mean plus 3 sigma 12 volt average current.
To compute the sum of the 12 volt mean current's 1 sigma value assume all the distributions are normal.
Therefore the square root of the sum of the squares calculation applies. Assume a case of 30
operations/second.
sigma
+12VDC (idle average) 0.02 amps
+12VDC (seek average) sqrt(30*((0.0002)**2))= 0.001 amps
TOTAL sqrt((0.02)**2+(.001)**2))=0.02 amps
So the mean plus 3 sigma mean current is 0.88 + 3*0.02 = 0.94 amps
Example 3. Power Calculation.
Nominal idle drive power = (1.26 Amps * 5 Volts) + (0.77 Amps * 12 Volts) = 15.54 Watts
Nominal R/W drive power at 30 ops/sec = (1.27 Amps * 5 Volts) + (0.88 Amps * 12 Volts) = 16.91
Watts
Mean plus 3 sigma drive power for 30 random R/W operations/second. Assume that the 5 volt and 12 volt
distributions are independent therefore the square root of the sum of the squares applies.
+5VDC (1 sigma power) 0.05 * 5 = 0.25 watts
+12VDC (1 sigma power) 0.03 * 12 = 0.36 watts
Total (1 sigma power) sqrt((0.25)**2+(0.36)**2) = 0.44 watts
Total power 15.46 + 3 * 0.44 = 16.8 watts
Source filename=POWERIBM CorporationPage 28 of 87