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Fig. 6.6 Offset
Fig. 6.7 Slope
6.7
Logic unit
The combination of a logic unit with its input parameter and connected output defines the
control channel (see Fig. 6.1). Connections can be established using the function keys or
the configuration tool.
The input of the logic unit can be set in the parameter
C.in
(PL-2 group).
If a value from d1 to d8 is selected, one of the device inputs is directly connected to the
LU. Also an average
value from 2 to 8 inputs (F1…F7), difference between 2 different
inputs (A1…A4) or rate of change (units/min.) for each input (r1…r8) can be selected. If
the logic unit should not be used, set the parameter
C.in
to OFF.
An additional differential filter for the LU input values r1…r8 “Rate of change” is applied.
The performance of this filter can be set in the parameter
in.rd
“Differential filter time
constant” (PL-1 group) for each input.
Each logic unit can be connected to one of 8 outputs, specified in the parameter
C.dr
(PL-2 group) for this LU. (for example see Table B.1, PL-
3 group “Standard configura-
tions”). Don’t forget that one output can be connected with several LUs and each of them
can switch the output on (OR logic).
Each LU can work in different modes defined in the parameter
AL.t
(PL-2 group):
– Measuring (
AL.t
= 0)
– Comparator
o
Heating (
AL.t
= 1)
o
Cooling (
AL.t
= 2)
o
Alarm within limits (
AL.t
= 3)
o
Alarm outside limits (
AL.t
= 4)
– Retransmission (
AL.t
= 5).
The LU connected to the output of I or U type can work only in Measuring or Retransmis-
sion modes. In the Measuring mode the LU transmits the input signal only to the display,
in the Retransmission mode
– to the connected output. Control signal is not generated.
If the logic unit works in one of the comparator modes it must be connected to a digital
output (R, S or T type).
6.7.1
Comparator mode
In the Comparator mode the LU compares the input signal with the setpoint considering
the hysteresis value
Δ and generates the output control signal. Setpoint and hysteresis
values are specified in the parameters
C.SP
and
HУSt
(PL-2 group).