USER RESPONSIBLE F O R V E R I F Y I N G VERSION A N D COMPLETENESS
O E M F U N C T I O N A L SPECIFICATION ULTRASTAR X P (DFHC) SSA M O D E L S 1.12/2.25 GB - 1.0" H I G H
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
+ 1 2 V D C (idle average)
0.77 amps
+ 1 2 V D C (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
+ 1 2 V D C (idle average)
0.02 amps
+ 1 2 V D C (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.
+ 5 V D C (1 sigma power) 0.05 * 5
= 0.25 watts
+ 1 2 V D C (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=POWER
IBM Corporation
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