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Remote Sensor Selection (J15)
When configured to operate with remote temperature sensors,
the Multi-SR is compatible with Sensors P1 through P9 shown
in the SmartFan Catalog. Control temperature is a function of
the temperature sensor selected and the position of the shunt
(S3) on header J15.
Board-Mounted Temperature Sensor
In this application, fan voltage is proportional to the temperature
sensed by the sensor that is soldered to the Multi-SR. Header
J17 is disabled.
Jumper Settings (J1, J11, J15, J18)
There are four jumper settings that must be reviewed prior to
applying power to the Multi-SR: Output Voltage, Control
Temperature, Alarm Speed and 3.3/5.0 On-Board I2C Power.
Settings are based on application and the configuration of the
Multi-SR. Following is a description of each jumper setting.
1) Control Temperature Setting (J15): The control
temperature is the temperature at which the maximum voltage is
applied to the fans. Header J15 allows selection from three
different control temperatures. Table 4.0 shows the control
temperature value for each jumper setting. If the jumper is
removed, the default setting is MED. Chart 1.0 shows fan
voltage vs. sensor temperature for each control temperature
setting.
NOTE: Header J15 is only applicable to Temperature Sensor
based fan control. The setting of this header can be ignored in
I2C based and PWM based fan control applications.
2) Output Voltage Setting (J1):
The Multi-SR can provide
power to either 48 VDC or 24 VDC fans from a 36 to 75 VDC
input voltage source. Use header J1 to select the type of fan
connected to the Multi-SR. Move the shunt to 24V if 24 VDC
fans are being used. Move the shunt to 48V if 48 VDC fans are
being used.
CAUTION: If the shunt is removed, the Multi-SR will
operate in the 24 VDC fan mode. It is not recommended that
the shunt be removed for any reason. A mix of 48 VDC and
24 VDC fans cannot be connected to the Multi-SR.
3) Fan Alarm Speed Setting (J11):The Multi-SR monitors the
tachometer signal inputs of up to six fans and activates the FAN
alarm if the speed of one or more fans falls below the trigger
speed (WA). One of three trigger speeds can be selected using
the jumper on header J11. Each jumper position is defined as
follows:
Position LOW = 1000 PPM
Position MED = 2000 PPM (Factory Setting)
Position HIGH = 4000 PPM
Since fan tachometer circuits are designed with one, two or even
more pulse outputs per revolution, settings are listed in pulses
per minute (PPM) rather than revolutions per minute (RPM).
Given the fan’s speed under load (W) and the number of pulses
per revolution (N), use the following formula to select the trigger
speed (WA):
WA = W x N x 0.3
For example, a 3300-RPM fan with two pulses per revolution
would have a trigger speed of
WA = 3300 RPM x 2PPR x 0.3 = 1980 PPM.
Since the 2000 PPM trigger is closest, set jumper J11 to the
“MED” position.
The alarm trigger accuracy is +/- 20%.
If the shunt is removed from header J11, the Multi-SR defaults
to the factory setting of 2000 PPM.
4) On-Board Isolated Power Setting (J18): The Multi-SR can
provide isolated 3.3 or 5.0 VDC power for the I2C Bus and
PWM/0-5 VDC input interfaces. Use header J18 to select the
power required. Move the shunt to 3.3 if 3.3 VDC power is
required. Move the shunt to 5.0 if 5.0 VDC power is required.
If the jumper is removed from header J18, the Multi-SR defaults
to 3.3 VDC power. NOTE: The position of the shunt on header
J18 is not applicable when isolated power is sourced externally.
Local Alarm Status Operation & Logic (J9)
Four alarm outputs, located at header J9, provide visual and
audible status of fan, temperature sensors and microprocessor
watchdog alarms. The failure criteria are defined in Table 5.0.
Table 6.0 shows the status of each LED output on header J9 for
failure and valid conditions based on using single color LEDs.
If bi-color LEDs are used, the LEDs would switch color rather
than turn ON/OFF.
Major/Minor Alarm Logic (J12)
Alarm logic for the optically isolated major and minor alarms on
header J12 is shown in Table 7.0. The values in the table are
based on the circuit configurations shown in Figure 3.0 (found on the Installation page).
“More than one failure” in Table 7.0 is defined as the presence
of any of the following conditions:
- One or more sensors read a high temperature or are open
and one fan has failed.
- A watchdog failure has occurred.
- Two or more fans have failed.
Fan Voltage in any Alarm Condition
During the presence of any alarm condition, the maximum fan
voltage is applied to the fans.
I2C Bus Protocol
The I2C Bus is configured as a slave device that can transmit
and receive data. When the Multi-SR is configured for I2C
based speed control, the user can write speed commands to the
Multi-SR and read all alarm status bits except the high
temperature status bits. When configured for temperature sensor
based control the user can read all alarm status bits from the
Multi-SR. When configured for PWM based speed control, the
user can read all alarm status bits but the high temperature status
bits.
Specifications
- The bus supports seven-bit addressing and only acts as a
slave device.
- The address for the fan controller is 0x0C (‘0001100’).
- General call support is not provided.
- The fan controller will stretch the clock further if needed.
- The hardware register will support Standard Mode I2C,
however, the system is tested at 55kHz clock speed and
lower clock speeds are recommended.
- Speed commands (when used) must be updated every 60
seconds or the fan voltage is sent to 100%.
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Table 8.0 defines the bits used in the serial bus protocol.
Reading Status Information
Table 9.0 provides the definition of each of the sixteen status
bits in the I2C protocol. The first byte, bits D7 – D0, provides
the status of all fans and minor alarm status. The second byte,
bits D15 – D8, provides temperature sensor and major alarm
status.
“More than one failure” in Table 9.0 is defined as the presence
of any of the following conditions:
- One or more sensors read a high temperature or are open
and one fan has failed.
- A watchdog failure has occurred.
- Two or more fans have failed.
Read First Alarm Status Byte: The following format is used to
read the first status byte (D7 – D0). Reading the first status byte
can be performed under all configurations of the Multi-SR
because it provides fan failure status, a feature common to all
configurations.
Format:
S A6 A5 A4 A3 A2 A1 A0 R ACK D7 D6 D5 D4 D3 D2
D1 D0 ACK P
Example: S 0 0 0 1 1 0 0 1 ACK 0 1 0 0 0 0 1 0
ACK P…Shows that the fan connected to J4 has
failed and the minor alarm status is active.
Read First and Second Alarm Status Bytes: The following
format is used to read the first and second status bytes (D7 – D0
& D15 – D8) of alarm status.
Format:
S A6 A5 A4 A3 A2 A1 A0 R ACK D7 D6 D5 D4 D3 D2
D1 D0 ACK D15 D14 D13 D12 D11 D10 D9 D8 ACK P
The first byte provides the status of each fan, a feature common
to all configurations of the Multi-SR. The status information
provided in the second byte is dependent on the configuration of
the Multi-SR:
If Configured for Temperature Sensor Based Fan Control,
the second byte of status information provides major and minor
alarm status, open sensor and over temperature sensor
information.
Example: S 0 0 0 1 1 0 0 1 ACK 0 1 0 0 0 0 0 0
ACK 1 0 1 1 0 0 0 0 ACK P…Shows no fan alarms,
sensors T3 and T2 are reading a high temperature
and as a result the minor alarm is active.
If Configured for PWM or I2C Bus Based Fan Control, the
second byte of status information provides major and minor
alarm status and ONLY open sensor status (D10 – D8). Since
no sensors should be connected to the Multi-SR (header J17)
under this configuration, only the presence of a sensor is
monitored as a safeguard. Therefore, each over temperature
status bit (D13 – D11) is always 0. But, if a sensor (reading > -
20°C) is connected to header J17, the corresponding open sensor
status bit will be 0 and minor alarm status bits will read 1.
Example: S 0 0 0 1 1 0 0 1 ACK 0 1 0 0 0 1 0 1
ACK 1 1 0 0 0 1 1 1 ACK P…Shows thermistors T3,
T2 and T1 are open and fans on headers J3 and J5
have failed causing a major and minor alarm to
be active.
Watchdog Status on I2C Bus
The watchdog/microcontroller alarm is not communicated on the
I2C Bus. A watchdog failure is a major alarm condition.
Therefore, remote detection of a watchdog alarm is available via
the major alarm logic circuit output located on header J12.
Writing Speed Commands
Table 10.0 shows the data format for writing a speed command
to the Multi-SR I2C Bus.
Use the hexadecimal values listed in Table 11.0 to control fan
voltage via the I2C Bus. Writing a hexadecimal number to bits
D0 – D7 changes fan voltage.
Write Speed Command Byte:
The following format is used to write a speed command to the
Multi-SR. Because of the way the I2C Bus is implemented, a
speed command is acknowledged by the Multi-SR under all
configurations but is ONLY executed when the Multi-SR is
configured for I2C Bus fan control. Speed commands must be
updated every 60 seconds or the fan voltage is sent to 100%.
Format:
S A6 A5 A4 A3 A2 A1 A0 W ACK D7 D6 D5 D4 D3 D2
D1 D0 ACK P
Example: S 0 0 0 1 1 0 0 0 ACK 0 0 0 0 1 0 1 0
ACK P…Shows a write command that sends the
Multi-SR to 85% speed.
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