7
Setting up the relay PI controller
The Relay Propor Integral Controller can be made to operate in either pulse width control
or frequency control mode via the
A
x
OPEr
function. Note that the
A
x
OPEr
function will not
be seen until a value has been set for the low or high alarm e.g. for
A1Lo
or
A1Hi
. The best
results are usually achieved by initially configuring as a “Proportional Only” controller and then
introducing the Integral functions when stable results are obtained.
Relay 1 and , if fitted, relay 2 can be set to operate in PI control mode. Any other relays fitted will
only operate in normal, non PI operation. The “
x
” in the
A
x
OPEr
and other functions indicates
the chosen relay i.e. for relay 1 the display will show
A1 OPER
,
A1.SP
etc. The
A
x
OPEr
function allows three choices of operating mode for the chosen relay, namely
A
x
.
AL
,
A
x
.
tP
and
A
x
.
Fr
. If
A
x
.
AL
is selected the chosen relay will operate as a setpoint relay whose operation is
controlled by the
A
x
Hi
,
A
x
Lo
etc. settings and the PI control settings will not be seen. See the
“Explanation of functions” chapter for details of operation when
A
x
.
AL
is selected. If
A
x
.
tP
is
selected then the chosen relay will operate in pulse width control mode. If
A
x
.
Fr
is selected then
the chosen relay will operate in the frequency control mode.
Pulse width control
- operates by controlling the on to off time ratio of the relay. In a typical
application this would be used to control the length of time for which a dosing pump is switched
on during a control cycle i.e. the pump or other device will continuously operate for the length of
time the relay is activated and will stop operating when the relay is de-activated.
Frequency control
- operates by changing the rate at which the relay switches on and off. In a
typical control application the frequency control operation is particularly suited for use when one
shot dosing is used i.e. the pump or other device puts out a fixed dosing quantity for every pulse
received.
7.1
Relay pulse width modulation control mode
To use pulse width modulation control
A
x
.
tP
must be selected at the
A
x
OPEr
function.
Relay
Relay
on
on
off
off
time
time
One control cycle
set by
x
A dc
Pulse width control
Proportional gain increased
leading to greater on time
for a given error.
Proportional gain
at a given value
38 of
RM4IVMAN-2.1-0
Summary of Contents for RM4-IV
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