7 - 28
emPC-A/RPI3
(
Hardware and
Software Manual)
•
Appendices
©
Janz Tec AG
Rev. 1.3
+5V (USB)
Max. 500 mA per USB port, max 500 mA for all USB ports
Environmental Specifications
To specify an ambient operating temperature for reliable 24/7 industrial operation,
the CPU and GPU load are two very important factors. If all CPU cores are idle all the
time, then the maximum specified ambient temperature can be much higher than in
a maximum CPU utilization application.
The new BCM2837 system-on-chip has much more computation power than its
predecessors, but also gets far, far hotter. In high CPU load scenarios, the clock is
dynamically increased from 600 MHz to 1200 MHz and then produces so much heat,
that even at room temperature the clock would automatically throttle down to 600
MHz after several minutes to prevent overheating.
Because of the thermal limitations of the used standard Raspberry Pi 3 Model B
single board computer, the form factor of the casing and the economic limitations in
this entry level system, no extensive passive cooling solution can be used. The
internal baseboard designed by us providing the power supply and the I/Os and two
fieldbuses to the Raspberry Pi board, would allow an ambient operating temperature
from -25 .. 60 C° but the Raspberry Pi board is the limiting factor.
The emPC-A/RPI3 uses a passive heat sink on the BCM2837 chip and therefore is it
not possible to use all of the computation performance the BCM2837 provides. The
CPU power consumption ranges from 1.5 W (average when idle) to 6.7 W (maximum
under stress), so to prevent CPU overheating and throtteling, the maximum CPU
power consumption should not be higher than about 4 W. In most real world use
cases of this embedded computer, the average CPU power consumption will be
lower than this limit, but if constant CPU performance is important for your
application, then limiting the maximum CPU frequency to 600 MHz in configuration
file /boot/config.txt is one possibility to achieve this. Without limiting the maximum
CPU frequency, the CPU will dynamically change the frequency depending on the
CPU temperature (see commands:
vcgencmd measure_temp
and
vcgencmd
measure_clock arm
).
Ambient Temperature
operating
0 .. +40 °C (vertical orientation / wall and DIN rail mounting)
0 .. +35 °C (horizontal orientation / desk-top mounting)
at sea level, derated by 1 °C per 300 m above sea level to a maximum
of 2000 m.
the above temperature ratings are defined under the following CPU
load:
•
No GPU load
•
4 cores loaded at 600 MHz or 1 core loaded at 1200 MHz,
where the load per core is comparable to that of the Linux
stress utility
•
The above numbers are without safety margins to compensate
process variations of the Broadcom SoC
•
More load will bring the CPU Junction temperature above 80
°C and the CPU will reduce clock frequency towards 600
MHz. The system will not overheat under such conditions.
Temperature storage
-20 .. +75 °C
2)
Humidity
5% .. 95% r.H., non condensing
