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GENERAL FEATURES:
The following features are common to all configurations of the
Multi-SR.
Input Power: The Multi-SR can accept one or two power
sources in the range of 36 to 75 VDC. If two power supplies are
used, they are logically OR’d on the Multi-SR so that the
operating voltage is equal to the higher of the two supplies. The
Multi-SR can supply up to 4.0 Amps to the fan load with natural
convection or 5.0 Amps to the fan load with 200 LFPM of
forced convection, at 24 VDC or 48 VDC.
Fan Speed Control: The speed of all fans is varied by adjusting
the fan voltage. Voltage adjustment is accomplished with a
current mode buck/boost control circuit. The fan voltage range
is 13-25 VDC for 24 VDC fans and 26-50 VDC for 48 VDC
fans.
Active Current Limiting: The load regulating circuitry is
configured with a 10 Amp active current limit. At the initial
application of power, a 10 Amp AC transient current having a
duration of less than two milliseconds can be expected. This
current transient can also be expected during a “hot-plug”
condition, where input power is rapidly cycled.
Input Power Fuse: A 10 Amp input power fuse is provided to
protect the Multi-SR from over-current conditions.
Soft Start: The voltage applied to the fans at start-up ramps
from 0 to 13 VDC for 24 VDC fans and 0 to 26 VDC for 48
VDC fans. After this period, the fan voltage moves to the
commanded voltage. This “soft start” feature limits the current
spike common to DC fans at start-up.
Communication of Alarm Status via I2C Bus: The status of
each fan and the MINOR and MAJOR alarms is available on the
I2C Bus.
SELECTABLE FEATURES:
The Multi-SR includes user selectable features that allow it to
meet a variety of telecommunication applications. The
selectable features that must be specified by the user prior to
ordering are listed below. Each Multi-SR is programmed prior
to shipment with the features selected.
Number of Fans: The Multi-SR can be configured to power
and monitor 1 to 6 fans.
Fan Control Methods:
Three methods of controlling the speed of the fans are available:
Temperature Sensor input, PWM/0-5 VDC input or I2C Bus
input. Following is a description of each control method:
1) Temperature Based Fan Control: The speed of all fans is
proportional to the highest temperature read by 1 to 3 remote
sensors connected to header J17 or the temperature of one board
mounted sensor. Chart 1.0 shows fan voltage as a function of
sensed temperature. A shunt on header J15 is used to select the
control temperature TC (The control temperature is the
temperature at which 100% fan voltage is applied to the fans.).
When temperature based fan control is selected, temperature
sensor status is available on the I2C bus.
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2) PWM/0-5 VDC Based Fan Control: The speed of all fans is
proportional to the PWM/0-5 VDC signal applied to header J16.
Chart 2.0 shows the relationship between the control signal
applied at header J16 and the fan voltage.
3) I2C Bus Based Fan Control: When configured for fan
control via the I2C Bus, the speed of all fans is mapped to the
command sent through the I2C on header J14. See the
Operation Section for a full definition of the I2C protocol.
Number of Temperature Sensors: When temperature sensor
based fan control is specified, the user can choose to control
based on 1, 2, or 3 remotely mounted sensors or one board
mounted sensor.
On Board Isolated Power Supply: The user can choose to
supply the 3.3 or 5.0 VDC power required to run the I2C Bus
(header J14) or PWM/0-5 input interface (header J16) or specify
that an isolated power supply be provided on-board.
Specialized Configurations of the Multi-SR
The following parameters can be specialized through software
modification:
- Relationship between sensed temperature and fan
voltage
- Relationship between PWM control signal and fan
voltage
- Fan speed control based on differential temperature
- Fan speed alarm trigger point
- Temperature alarm trigger point
- I2C Bus status register
- Fan turn off below XXC
Customized Configuration of the Multi-SR
Contact Control Resources’ Application Engineering for details.
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