937B Controller Instruction Manual
pg. 55
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 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 937B 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.