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OEM FUNCTIONAL SPECIFICATION ULTRASTAR XP (DFHC) SSA MODELS 1.12/2.25 GB - 1.0" HIGH
2.2.2.1 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) 0.41 amps
+12VDC (seek average) 0.0031 * 30 = 0.09 amps
TOTAL 0.50 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 0.50 + 3*0.02 = 0.56 amps
Example 3. Power Calculation.
Nominal idle drive power = (1.23 Amps * 5 Volts) + (0.41 Amps * 12 Volts) = 11.07 Watts
Nominal R/W drive power at 30 ops/sec = (1.25 Amps * 5 Volts) + (0.50 Amps * 12 Volts) = 12.25
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) 0.02 * 12 = 0.24 watts
Total (1 sigma power) sqrt((0.25)**2+(0.24)**2) = 0.35 watts
Total power 10.8 + 3 * 0.35 = 11.9 watts
Source filename=POWERIBM CorporationPage 22 of 87