TAC AB, 1998-10-23 0-004-7614-0 (GB), 7:9 (24)
TAC 2413 Handbook Functional description
7.3.6 CO
2
/ SPC
This function is chosen by using parameter P 55; 0 = no function,
1 = SPC, and 2 = CO
2
.
By connecting an external 2–10 V DC control voltage to the SPC in-
put, the current setpoint can be shifted, see the figure below.
There is no change to the setpoint at 6 V, but 2 V and 10 V provides
the set effect with a – or + sign. This means that 2 V will give the (–)
effect and 10 V will give the (+) effect. However, an input signal that
is < 1.5 V will achieve the same effect as 6 V, that is no change to the
setpoint.
When CO
2
is chosen, the air quality is controlled by comparing the
measured signal 0-10 V from a carbon dioxide sensor with an
adjustable value, P 57. As long as return air control is not chosen,
full speed is activated at this setpoint and deactivated with 1 V mi-
nus the hysteresis.
When return air control has been chosen, the damper is controlled
towards its open position by using the P function. The P band is
calculated symmetrically around the setpoint ±1 V. When the in-
put signal is 1 V less than the setpoint, the damper control starts.
For example, if the setopint is 4 V, the damper starts to open at 3 V
and the full control signal is achieved at an input signal of 5 V. If
there is not a significant change (5 %), either an increase or de-
crease, of the CO
2
concentration, the damper is allowed to remain
in its current position, which eliminates unneccessary interven-
tion. The minimum limitation controller for the supply air tempe-
rature limits the opening of the damper.
Full speed is activated at 10 V control signal and deactivated with 1 V
minus the hysteresis. Full speed is disabled if the outdoor temperature
is less than the set limit P90.
123
4
5678910
-4,0
-3,0
-2,0
-1,0
0,0
1,0
2,0
3,0
4,0
5,0
Setpoint adjustment effect (°C)
SPC signal (V)
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