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OEM FUNCTIONAL SPECIFICATION ULTRASTAR XP (DFHC) SSA MODELS 1.12/2.25 GB - 1.0" HIGH
Example 4. Calculate the 12 volt peak current.
To compute the sum of the 12 volt peak currents the following is done.
mean
+12VDC (idle avg) 0.77 amps
+12VDC (seek peak) 1.3 amps
TOTAL 2.07 amps
Example 5. Calculate the mean plus 3 sigma 12 volt peak current.
To compute the sum of the 12 volt peak current's 1 sigma value assume all distributions are normal. There-
fore the square root of the sum of the squares calculation applies.
sigma
+12VDC (idle avg) 0.02 amps
+12VDC (seek peak) 0.02 amps
TOTAL sqrt((0.02)**2+(0.02)**2)=0.028 amps
So the mean plus 3 sigma peak current is 2.07 + 3*0.028= 2.1 amps
Things to check when measuring 12 V supply current:
Null the current probe frequently. Be sure to let it warm up.
Adjust the power supply to 12.00 V at the drive terminals.
Use a proper window width, covering an integral number of spindle revolutions.
Measure values at 25 degree C casting temperature.
Get a reliable trigger for Seek Peak readings.
Source filename=POWER IBM Corporation Page 29 of 87