Switchover Between Automatic And Direct Operation; Speed Switching Logic - ABB i-bus FCC/S 1 1 Series Product Manual

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ABB i-bus KNX
Planning and application
On a fan with speed switching or changeover switching, the individual speed is controlled as fol-
lows:
The speeds are controlled via the following values for a 3-speed fan:
• Speed 0: 0 (0 %)
• Speed 1: 1...85 (1...33 %)
• Speed 2: 86...170 (34...67 %)
• Speed 3: 171...255 (68...100 %)
The speeds are controlled via the following values for a 2-speed fan:
• Speed 0: 0 (0 %)
• Speed 1: 1...128 (1...50 %)
• Speed 2: 129...255 (51...100 %)
The speeds are controlled via the following values for a 1-speed fan:
• Speed 0: 0 (0 %)
• Speed 1: 1...255 (1...100 %)
With a continuous fan, the desired speed is entered directly and transmitted to the fan.
1-byte value
0
1...85
86...170
171...255
Table 38: Fan speed depending on the entered value
12.2.5

Switchover between automatic and direct operation

Switchover between automatic operation and direct operation is possible. The changeover to man-
ual fan control is implemented via a 1 bit value or automatically after a certain time period elapses.
The fan speed is switched in accordance with the 1-byte value received.
Fan control is changed back to automatic operation if a 1 is received on the respective group ob-
ject.
The current status of automatic operation is fed back via a 1 bit value.
12.2.6

Speed switching logic

The control value for changing the speed is calculated as follows:
• Switching up: control value ≥ threshold + 1/2 hysteresis
• Switching down: control value ≥ threshold + 1/2 hysteresis
The value 0 is an exception. If this is selected as the switchover point between 0 and 1, switching
up (0 > 1) takes place only from a control value greater than 0 and switching down (1 > 0) only
from a control value equal to zero.
The following additionally applies:
• Switching always takes place to the highest speed with 100 %
• The fan is always switched off at 0 %.
The following example describes the sequence of speed switchover depending on the control
value and the parametrized thresholds and hysteresis values.
Percent Hexadecimal
0 00
1 %...33 % 55
34 %...67 % AA
68 %...100 % FF
Binary value bit
76543210
00000000
00000001 ...
01010101
01010110 ...
10101010
10101011 ...
11111111
FCC/S 1.X.X.1 | 2CDC 508 200 D0211 Rev A 361
Fan speed
0 (OFF)
Fan speed 1
Fan speed 2
Fan speed 3