Technical Manual Stage Controller MSR
eco
3140
Page 11
Functional Description
Input Signals of the Controller
The input signals come from a 2-wire pressure
transmitter with a 4-20 mA signal or one of the four
(4) temperature probes. The source can be selected
at
h21
...
h26
(Assignment page).
If a pressure transmitter is selected, additionally
a refrigerant must be defined (at
h99
), which is
necessary to calculate a temperature in °C.
Calibration of Transmitter, Display Correction
For each transmitter input must be defined, which
pressure corresponds to the delivered 4-20 mA
signals.
4-20mA Input
For this inputs, the matching pressure limits can
be set by
h93
,
h94
(pressure transmitter input 1)
and
h95
,
h96
(pressure transmitter input 2).
Probe-/Transmitter Failures
If a probe or transmitter failure is identified, all stages
will switch ON with the selected delay.
After the alarm delay
r08
, the alarm relay (
ALA
)
switches off if it is defined and available.
Control of Compressors (Load)
The MSR
eco
is able to control up to 8 (with extension
module BMR 3002) single or multi-stage loads with
up to four stages.
The kind and number of stages of the selected
loads must be defined with the parameters
h51
up
to
h58
.
Example:
Standard Stage Controller
Applications include:
- Standard compressors
- Compressors with
CRII Control Stages / Power Control
- Condensation High Pressure Control
Standard Compressors (SP)
The control setpoint is preset by
r01
(day) or
r02
(night). With
r03
a maximum value for this setpoint
can be determined. The range of the hysteresis can
be set using parameter
r04
, while
r05
determines
the position above the set point, (above, below, or
balanced).
Forerun (Stages ON)
If the actual value exceeds the switching point,
then the forerun delay starts (
r41
...
r48
, individual
for each stage). After this timer is run down, a stage
will be switched ON and the individual delay time
starts again.
Neutral Zone
If the actual value is located within the hysteresis
range
r04/r05
, no stage will be activated or
de-activated.
Backrun (Stages will switch OFF)
If the actual value falls below the tripping point,
the backrun delay (
r51
...
r58
, individual for each
stage) will be started. After this timer is run down,
one stage will switch OFF and the individual delay
time starts again.
L21
shows the current state of the
controller.
Limits
If the actual measured value falls to a critical
level, the controller will react in two ways:
If the actual value falls below the Early Warning
Alarm setpoint, parameter ‚
r07
‘, then at least 50%
of the motors will switch off, once the set time of
parameter ‚
r08
‘ is reached.
If the actual value falls below parameter ‚
r06
‘,
then a forced Backrun will also be initiated,
shutting down all motors.
Compressor
Programming Relay selection
free at
h51 h52 h53 h54
h01 ... h05
4x single mach.
1 1 1 1
2x dual stage
2 2 0 0
1x 3-stage
3 0 0 0
1x 3-stage and
1x single mach.
3 1 0 0
Base Load Change / Switching Frequency Opt.
If a plant is laid out correctly, then not all fans and
compressors should run continuously. When
using normal stage controllers, some motors bear
a heavy load while other hardly any load at all. To
prevent this, the „Base Load Change“ function can
be utilized. (This function is also known as Stage
Sequencing).
The „
r22
“ parameter monitors the relative run
times of the motors and will establish a consistent
balance of approximately the same runtime for
each motor. Different application scenarios can be
selected. If a multistage unit is being used, only
the runtime of the leading stage, (=motor on) will
be calculated.
The control system records and stores the runtime
and downtime of each motor to determine which
motor can be switched on or off.
During „Backrun“ operation, the motor with the
longest run time will be switched off first. For the
„Forerun“ operation, the option exists to select the
motor based on (
a
) shortest runtime, or (
b
) longest
downtime.
If the pressure ratio in the plant does not change
over a long period of time, no 'Forerun/Backrun' is
active and a sequencing is impossible. The 'Delay
Time (
r20
) starts a short backrun after the set time
to enable a new motor selection.
It is also possible to select an optimization function,
(
c
), for the switching frequency. If the optimization
function is activated, during backrun, the controller
switches off an additional stage on a compressor
before a motor is switched off.
Thus, a more uniform utilization can be
achieved without any particular motor car-
rying an unnecessary higher load.
With
r21
an Operational-Feedback Time can be
set, which determines when a feedback signal
must be recognized.
Minimum Idle Time
If a motor is switched off, it can be restarted after a
Minimum Idle Time (
r71
...
r78
).
Control of Compressors with
CRII-System Power Control
This control method can be activated by the pa-
rameter "
h49
". With this method, only one of the
compressors can be controlled.
Characteristic for this compressor type is the fact that
the first stage generates no refrigeration capacity.
The control of the refrigeration capacity is achieved
by a fast on/off switching of the power stages.
Control
The control of the CRII-Valves is always inverted,
that means if voltage appears at the corresponding
output, the respective power stage is deactivated.
The switching behaviour must be set separately
for each power stage (inverted for CRII-power
stages,
h61
...
h68
).
While a standstill, the CRII-Valves of the motor will
be de-energized. With the start of the motor the
switching outputs of the power stages will be
utlized at the same time.
If the motor runs without power stages, an
adjustable „switch-off“ countdown "
r24
" will be
initiated. Once the set amount of time is depleted,
the motor will be switched off.
The controller performs regular sequence
exchanges to ensure the CRII Valves switch an
equal number of times.
The forerun/backrun behaviour is the same as at
the standard application.
Toggling of Power Stages
If the power requirement develops in the way that
a power stage switches repeatedly, the forerun/
backrun delay times are not used, but the
respective stage can be switched on/off
immediately after "
r23
“ (
Idle Time of the stage with
0% load
).
Base Load Change with Switching Frequency
Optimization at Backrun
Due to the special requirements of the control de-
pending on the basic stage, the Switching
Frequency Optimization does not work and must
be de-activated. So only the values "000, rr0, hr0“
are allowed for the parameter "
r22
“.
"rr1" and "hr1" are treated as "rr0" and "hr0"
respectively.
Condensation High Pressure Control (HP)
The Condensation High Pressure Control can
be used with the analogue output as P-controller
and/or with up to 8 relay stages. The relay stages
can be assigned to up to 8 machines. For each
stage a forerun delay time (
d41
...
d48
), a backrun
delay time (
d51
...
d58
) and a setpoint (
d01
...
d08
)
is available. Each motor can be set to manually/off/
automatic (
d61
...
d68
) as well as a minimum idle
time (
d71
...
d78
).
The HP function has the same base-load change
function and switching optimization as the SP
function. HP operates with an unified control
hysteresis (
d12
) and hysteresis position (
d13
),
relative to the active setpoint.
Depending in the number of stages that are on, the
On/Off Switch position will be depended on the
respective setpoint - hysteresis respectively the
next se hysteresis. With it, the position of
the hysteresis is taken into account. When using
the analogue output P Controller, the proportional
range is determined by the switch-on/off positions
of the respective stage, depending on the number
of running stages. If the configuration has only one
or zero stages, the switch-on/off positions are
represented by the first setpoint and the hysteresis
of the stage controller only.
Two (2) limit values 'High pressure alarm limit'
(
d17
) and 'High pressure pre alarm limit' (
d18
)
generate error messages when exceeded.
If
d18
is exceeded, a load limitation of the SP
machines will be activated to max 75% of the
selected machines. If
d17
is exceeded, all SP
motors will be switched off by fast backrun.
Minimum Overheat Monitoring (SP)
In order to avoid insufficient overheat, and the po-
tential for liquid refrigerant to flow into the suction
tube, in systems where there may not be enough
compressor power to create sufficient overheat,
the „Minimum Superheat Threshold“, parameter
‚
P10
‘ should be used. When the established mini-
mum limit is not reached, an alarm will be triggered
and the expansion valves of the cooling positions
will be locked with special settings.
An additional temperature probe (Sut) would need
to be installed at the suction tube. The suction gas
overheat will be calculated using the measured
temperature value at the suction tube and the
suction pressure transmitter.
If ‚
P10
‘ is not reached, and ‚
P12
‘, („Superheat
Warning Delay Timer“) times out, then an „SSG
Warning“ alarm will be activated, and if needed,
the cooling positions will be locked.
The backrun of the last running compressor stages
will not be generated at the standard switch point,
but the compound sucks up to the defined suction
pressure pre-warning setpoint, and switches off
without delay.
If the overheat has reached the defined limit value
+ hysteresis, the warnings and cooling position
locks will be canceled.
If the overheat falls below a second limit value
(Compound lock threshold minimal superheat,
P14
), which is smaller than the first limit value,
after the settable delay time (
P15
) a fast backrun
of the compound will be started and an alarm 'SSG
fault' appears.
The delay for the switch-off starts earliest, after
the alarm delay (
P12
, warn delay superheat) has
been run down. The compound will be released if
the second limit value has been reached again or
exceeded.
