Siemens RS-485 - Manual (Page 14)

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Siemens Building Technologies CC1A7865.1en
HVAC Products 31.10.2002
Modulating controller:
The management system predefines the value (degree of modulation) for the analog
output via «RY».
Setting the «RK2» and «RK3» by the management system has no impact.
Both relays «K2» and «K3», are deenergized.
Floating step controller:
The management system controls the actuator («RK2» and «RK3», relays «K2» /
«K3»).
Setting the «RY» by the management system has no impact. In that case, the analog
output delivers 0 V or 0 / 4 mA.
The RWF40... always checks to ensure that «RK2» and «RK3» (opening / closing) are
not activated simultaneously. In such a case, the response is «K2 = K3 = deener-
gized».
If both relay contacts change their position during the controller’s sequence time, the
output is «K2 = K3 = deenergized». This time contact interval («K2 = K3 = off» for one
scanning time) is also permitted in 2-stage operation.
The remote relay commands «RK2» and «RK3» (relays «K2» / «K3») control the
opening and closing travel of the controlling element. Using parameter «RSTEP», the
management system predefines the required number of control cycles.
Output «K2» (opening) is controlled by a travel command and a positive number.
Output «K3» (closing) is controlled by a travel command and a negative number.
The number gives the number of RWF40... scanning cycles (210 ms) with which the
output is controlled.
The travel command with number 0 deenergizes immediately «K2» and «K3».
If a new travel command is given before the control time has elapsed, the RWF40...
ascertains the direction of rotation requested by the command. If the direction of rota-
tion does not change, the control time will immediately be replaced by the new value. If
the direction of rotation must be reversed, the controlled output will be dactivated and,
for the next scanning cycle, the appropriate control time is used (time contact interval).
If, simultaneously with the control strategy for the floating output, outputs «K2» and
«K3» (via «RK2» and «RK3») are directly set by the management system, the relay
information from the control strategy and output information «K2» and «K3» have a
logic «OR» connection. «RK2» and «RK3» (opening / closing) must never be energized
simultaneously. In such a case, the response is «K2 = K3 = denergized».
In operating mode «FULLY REMOTE», the management system ensures burner con-
trol. The RWF40... monitors the actual value to make certain the switching hystereses
will be observed.
If the actual value crosses the upper switch-off threshold, the management system will
be locked (status flag, «Management system locked» can be read via the interface).
The management system is released again when the actual value returns to a level
below the switch-on threshold.
If supervision of the actual value is not desired, the switching hystereses in the
RWF40... must be set to the respective maximum value.
In operating mode «REMOTE SETPOINT», the control algorithm ensures this kind of
supervision.
Mudulating burner
Control strategy for
floating output with
modulating burner
operation
Supervision of actual
value by setpoint-
dependent switching
thresholds
ã2002 Siemens Building Technologies
Subject to change!