Danfoss FC 102 Design Manual page 37

Introduction to VLT® HVAC D...
2.8.5 Local (Hand On) and Remote (Auto
On) Control
The frequency converter can be operated manually via the
local control panel (LCP) or remotely via analog/digital
inputs or serial bus.
If allowed in 0-40 [Hand on] Key on LCP, 0-41 [Off] Key on
LCP, 0-42 [Auto on] Key on LCP, and 0-43 [Reset] Key on LCP,
it is possible to start and stop the frequency converter by
LCP using the [Hand On] and [Off] keys. Alarms can be
reset via the [Reset] key. After pressing [Hand On], the
frequency converter goes into Hand Mode and follows (as
default) the local reference set by using [
After pressing [Auto On], the frequency converter goes
into Auto mode and follows (as default) the remote
reference. In this mode, it is possible to control the
frequency converter via the digital inputs and various serial
interfaces (RS-485, USB, or an optional fieldbus). See more
about starting, stopping, changing ramps and parameter
set-ups etc. in parameter group 5-1* Digital Inputs or
parameter group 8-5* Serial Communication.
Hand
O
on
Illustration 2.25 Operation Keys
Hand Off 3-13 Reference Site
Auto
LCP Keys
Hand Linked to Hand/
Auto
Hand ⇒ Off
Linked to Hand/
Auto
Auto Linked to Hand/
Auto
Auto ⇒ Off Linked to Hand/
Auto
All keys Local
All keys Remote
Table 2.14 Conditions for Either Local or Remote Reference
MG11BC02
Design Guide
▲ ▼
] and [ ].
Auto
Reset
on
Active Reference
Local
Local
Remote
Remote
Local
Remote
Danfoss A/S © Rev. 06/2014 All rights reserved.
Table 2.14 shows under which conditions either the local
reference or the remote reference is active. One of them is
always active, but both cannot be active at the same time.
Local reference forces the configuration mode to open
loop, independent on the setting of 1-00 Configuration
Mode.
Local reference is restored at power-down.
2.8.6 Control Structure Closed Loop
The internal controller allows the frequency converter to
become an integral part of the controlled system. The
frequency converter receives a feedback signal from a
sensor in the system. It then compares this feedback to a
setpoint reference value and determines the error, if any,
between these 2 signals. It then adjusts the speed of the
motor to correct this error.
For example, consider a pump application where the
speed of a pump is to be controlled so that the static
pressure in a pipe is constant. The desired static pressure
value is supplied to the frequency converter as the set-
point reference. A static pressure sensor measures the
actual static pressure in the pipe and supplies this to the
frequency converter as a feedback signal. If the feedback
signal is greater than the set-point reference, the
frequency converter slows down to reduce the pressure. In
a similar way, if the pipe pressure is lower than the
setpoint reference, the frequency converter automatically
speeds up to increase the pressure provided by the pump.
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