INFICON VGC403 Three-Channel Measurement and Control Unit - Manual (Page 21)

tinb07e1-e 2011-07 Vacuum Gauge Controller
21
5 Parameter
5.1 Switching function
parameters (PArA SP)
This parameter group allows you to configure the switch-
ing functions. The following switching function parame-
ters are available in the VGC402:
• SP1-L
• SP1-H
• SP2-L
• SP2-H
• SP3-L
• SP3-H
• SP4-L
• SP4-H
In addition, the VGC403 is equipped with the following
switching function parameters:
• SP5-L
• SP5-H
• SP6-L
• SP6-H
5.1.1 Fundamental terms
Switching functions
The VGC402 is equipped with four relays which switch in
dependance of the measured pressure. The relay con-
tacts are potential-free and can be used for switching via
the RELAY connection. See Chapter 3.3.5 RELAY,  13.
In this context we speak of the switching functions 1…4.
The VGC403 contains a total of six switching function
relays, i.e. the switching functions 1…6 are available in
this unit.
Threshold values
The switching behavior of the individual relays is deter-
mined by two parameters each: The lower threshold
value and the upper threshold value of the switching func-
tion.
• Lower threshold value SP-L:
The lower threshold value is responsible for activating
the assigned switching function. The relay switches
on as soon as the pressure falls below the lower
threshold value. This means that the common contact
of the relay is connected to the make contact.
• Upper threshold value SP-H:
The upper threshold value is responsible for deacti-
vating the assigned switching function. The relay
switches off as soon as the pressure rises above the
upper threshold value. This means that the common
contact of the relay is connected to the make contact.
Hysteresis
In the pressure range between the two threshold values,
the previous relay state is maintained. The relay does not
switch in this range, and the relay state depends on the
pressure curve history. See Fig. 5-1,  21.
Fig. 5-1 Behaviour of a switching function when the pressure
changes
p Pressure
t Time
NO make contact (normally open)
COM common contact
NC break contact (normally closed)
The region between the threshold values generates a
hysteresis (lag) between activating and deactivating of
the relay. The hysteresis prevents the switching function
from rapidly switching on and off when the pressure is
close to one of the threshold values.
p
t
SP-H
SP-L
NO
COM
NC
NO
COM
NC
NO
COM
NC