946 Controller Instruction Manual
pg. 79
the sequence repeating. Such an operation is detrimental to system control and should be
avoided.
Thus, when direction is set to ABOVE, the hysteresis must be lower than the set point, while
when the direction is set to BELOW, the hysteresis must be higher than the set point.
When Direction is changed, hysteresis is set to a default value (of about 10%). Depending on the
application, this value may need to be optimized. Default values depend upon the sensor type.
Information on specific defaults is given in Section 6-5 for each sensor.
8.1.3 Relay Inductive Loads and Arc Suppression
If the set point relay is used to switch inductive loads, e.g., solenoids, relays, transformers, etc., arcing of
the relay contacts may interfere with the controller operation or reduce relay contact life. In these
situations, an arc suppression network, shown schematically in Figure 8-2, is recommended.
Figure 8-2 The Relay Arc Suppression Network
The values of the capacitance
C
and the resistance
R
are calculated using the equations:
E
a
and
I
E
R
I
C
a
50
1
10
;
10
2
where
C
is in µF,
R
is in Ω,
I
is the DC or AC
peak
load current in amperes,
E
is the DC or AC
peak
source
voltage in volts.
C
min
= 0.001µF and
R
min
= 0.5 Ω.
8.2 Connecting the 946 Analog Output
Analog output signals, which can be sent to a data acquisition system, are available from each sensor.
These signals can be accessed from the 37 pin D-sub analog connector on the back of the controller.
They include buffered, logarithmic, and combination logarithmic output. Buffered and logarithmic analog
outputs are simultaneously available from all sensors. The detailed assignment for these pins is
described in Table 8-2.