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6.3
Power dissipation
Typical power dissipation under idle conditions is 17.05 watts (58.18 BTUs per hour).
To obtain operating power for typical random read operations, refer to the following I/O rate curve (see Figure
5). Locate the typical I/O rate for a drive in your system on the horizontal axis and read the corresponding +5
volt current, +12 volt current, and total watts on the vertical axis. To calculate BTUs per hour, multiply watts by
3.4123.
1.800
1.600
1.400
1.200
1.000
0.800
0.600
0.400
Figure 5.
DC current and power vs. input/output operations per second
6.4
Environmental limits
Temperature and humidity values experienced by the drive must be such that condensation does not occur on
any drive part. Altitude and atmospheric pressure specifications are referenced to a standard day at 58.7°F
(14.8°C). Maximum wet bulb temperature is 82°F (28°C).
6.4.1
Temperature
a. Operating
With cooling designed to maintain the case temperatures of Table 2, the drive meets all specifications over
a 41°F to 122°F (5°C to 50°C) drive ambient temperature range with a maximum temperature gradient of
36°F (20°C) per hour. The enclosure for the drive should be designed such that the temperatures at the
locations specified in Table 2 are not exceeded. Air flow may be needed to achieve these temperature val-
ues (see Section 8.4 and 8.4.1). Operation at case temperatures above these values may adversely affect
the drives ability to meet specifications.
The MTBF specification for the drive is based on operating in an environment that ensures that the case
temperatures specified in Table 2 are not exceeded. Occasional excursions to drive ambient temperatures
of 122°F (50°C) or 41°F (5°C) may occur without impact to specified MTBF. Air flow may be needed to
achieve these temperatures (see Section 8.4.1). Continual or sustained operation at case temperatures
above these values may degrade MTBF.
To confirm that the required cooling for the electronics and HDA is provided, place the drive in its final
mechanical configuration, perform random write/read operations. After the temperatures stabilize, measure
the case temperature of the components listed in Table 2 (see note [2]).
The maximum allowable HDA case temperature is 60°C. Operation of the drive at the maximum case tem-
perature is intended for short time periods only. Continuous operation at the elevated temperatures will
reduce product reliability.
0
50
100
I/Os per Second
Cheetah 73FC Product Manual, Rev. C
5V A
12V A
Watts
23
21
19
Watts
17
15
150
200
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