ECKELMANN VS 300 - Control Algorithm with Low-Pressure Control

Function of VS 300
23
Doku-Version 2.05 - Firmware 2.10 - 15. September 2017
4.3.3 Control algorithm with low-pressure control
The controller cycle time is 1 second. The control algorithm depends on the control type.
In the wet vapor range, temperature is a clear function of refrigerant and pressure: t = f (p, refriger
ant). The VS 300 calculates temperatures from the measured pressures as a function of the refriger
ant used. Exclusively temperature values are used for control. Temperatures (t
0
, t
c
) therefore stand
for pressures (p
0
, p
c
) in the system documentation.
4.3.4 Control algorithm with step controller
Low pressure measured by an A/D converter is compared with the setpoint (see section 4.3.10 Determining the
Low-Pressure Setpoint). The relationship is as follows:
Controlerror 
Time
Suction pressure
t
0 Setp
- 1,0 NZ
t
0 Setp
- NZ0,5
t
0 Setp
+NZ0,5
t
0 Setp
+ 1,5 NZ
Step
up
No step Step
down
No step
t
0 Setp
Control algorithm LP step controller
ZNR. 51203
64 030 F2
t
0
(D)
Neutrale Zone (NZ)
(A) (B) (C) (D) (E) (F)(G) (D)
(A) At a pressure greater than the actual value plus 0.5 times the neutral zone (NZ) and less than the actual
value plus 1.5 times the NZ, the step switching mechanism actuates stages in the event of a positive pressure
change.
(B) At a pressure greater than the setpoint value plus 1.5 times the NZ, the step switching mechanism actuates
stages, independent of the pressure change. This results in the compressors being activated in the order of
their operating times (compressor with the shortest operating time first).
(C) In the event of a fall in pressure less than the setpoint value plus 1.5 times the NZ and greater than the set
point value plus 0.5 times the NZ, no compressor actuation occurs as it is to be expected that the NZ will shortly
be reached.
(D) In the NZ no compressor actuation occurs.
(E) At a pressure less than the setpoint value minus 0.5 times the neutral zone (NZ) and greater than the set
point value minus 1.0 times the NZ, and in the event of a negative pressure change, the step switching mecha
nism switches down stages.
(F) At a pressure less than the setpoint value minus 1.0 times the NZ, the step switching mechanism switches
down a stage, independent of the pressure change. This results in the compressor with the longest operating
time being disabled.