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5.7 Medium pressure regulation
The controller regulates the medium pressure (MP) of a CO
2
system using a PI controller. The analogue output
2 (terminals 55/56
, 0..10 Volt)
is available for the output of the correcting variable.
5.7.1 Regulation
The control signal for the MP control valve is calculated using a PI controller. The amplification factors
P-factor
,
I-factor
and the time interval for the formation of the I-component
Interval
I
can be configured using the menu
3-2-3. The valve is closed if the "
Device OFF
" input is active. The MP control valve can also be operated in
manual mode. Using the parameter
Man. op. xxx %
in menu 3-2-3 MP Regulation, the valve opening degree
can be set from 0...100%. If "--" is entered, the opening degree is controlled via the PI controller. The manual
mode is only used for test and service purposes.
In the event of failure of the MP transmitter, a voltage of 0 Volt is applied at the output for the MP control valve.
5.7.2 Medium pressure shift / monitoring of minimum superheat
Introduction
A minimum superheat guarantees safe operation of the compressor on the suction side. If this minimum
superheat no longer takes place, an alarm is signalled that does not have an effect on the control action. The
minimum suction gas superheat is monitored using two suction gas temperature sensors via the terminals
33/34 (ÜH
k
) and 27/28 (ÜH
v
) and covers a temperature range of -50 .. 200 °C. Two superheat values (ÜH
k
and
ÜH
v
) result from this that are monitored separately.
Restrictions
•
When all compressors are idle, these error messages are blocked.
•
The function can only be used for a system configuration of up to maximum 9 compressors.
Monitoring of the medium pressure shift / minimum superheat
The following setpoints exist for the monitoring of the minimum superheat:
Configuration
Parameter
Menu Value range Default Unit Description
Min.OH-C
3-3
2..15
4
K Minimum permissible superheat on the case side
Del.Min.OH-C 3-3
1..30
10
Min. Message transmission delay for the message ÜH-K too small
Min.OH-P
3-3
2..15
4
K Minimum permissible superheat on the compressor side
Del.Min.OH-P 3-3
1...30
10
Min. Message transmission delay for the message ÜH-V too small
"OH" stands for superheat, the "C" stands for cases and the "P" for pack:
•
OH
c
: Suction pressure superheat between flash gas line and cases
•
OH
p
: Suction pressure superheat between flash gas line and compressor
Содержание VS 3015 C
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