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5.4.1 Control algorithm for LP control
The control algorithm depends on the type of control.
5.4.2 Control algorithm with LP step controller
The low pressure measured via an A/D converter is compared with the setpoint:
(A) At a pressure greater than the setpoint plus 0.5 times the neutral zone (NZ) and less than the setpoint plus
1.5 times the NZ, the step switching mechanism loads stages in the event of a
positive
pressure change.
(B) At a pressure greater than the setpoint plus 1.5 times the NZ, the step switching mechanism loads stages
independently
of the pressure change.
(C) In the case of falling pressure that is less than the setpoint plus 1.5 times the NZ and is greater than the
setpoint plus 0.5 times the NZ, no compressor switching is performed.
(D)
No
compressor switching is performed in the NZ.
(E) At a pressure less than the setpoint value minus 0.5 times the neutral zone (NZ) and greater than the
setpoint value minus 1.0 times the NZ, and in the event of a
negative
pressure change, the step switching
mechanism switches down stages.
(F) At a pressure less than the setpoint minus 1.0 times the NZ, the step switching mechanism unloads stages
independently
of the pressure change.
(G) In the case of increasing pressure that is between the setpoint minus 1.0 times the NZ and is greater than
the setpoint minus 0.5 times the NZ, no compressor switching is performed.
Neutral zone with compressor step control
If the low pressure regulation is performed using step controllers, no compressor switching is performed while
the control error is within a configurable
Dead band
.
If the low pressure regulation is performed using combined control, no switching of the fixed-speed
compressors is performed within the neutral zone.
In the wet vapour range, the temperature is a clear function of the pressure: t = f (p, R744). The
controller calculates temperatures for the LP range from the recorded pressures. Temperature values
are used exclusively for the regulation. Temperatures (t
0
/t
c
) thus substitute for pressures (p
0
/p
c
) in
this manual.
Содержание VS 3015 C
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