Watlow Series SD Limit - Manual (Page 44)

Set Point Low Limit and High Limit
The controller constrains the limit set point to a val-
ue between a low limit and a high limit. The high limit
cannot be set higher than the sensor range high limit or
lower than the sensor range low limit. The low limit
cannot be set lower than the sensor range low limit or
higher than the sensor range high limit.
Set the limit set point range with Set Point Low
[SP;Lo] and Set Point High [SP;hi] (Setup Page).
Process Input High and Low Scale
When an analog input is selected as a process volt-
age or process current input, you must choose the value
of voltage or current to represent the low and high end
values. For example, when using a 4 to 20 mA input,
the scale low value would be 4.00 mA and the scale high
value would be 20.00 mA. Commonly used scale ranges
supported by the Series SD limit are: 4 to 20 mA and 1
to 5V. The maximum current scale is 20 mA and the
maximum voltage scale is 10V. The minimum current
scale is 4 mA and the minimum voltage scale is 1V.
These minimum scale values allow the limit to detect a
loss of the process input signal. The Series SD limit will
not work with 0 to 20 mA, 0 to 5V or 0 to 10V process
signals.
The Series SD limit allows you to create a scale
range for special applications other than the standard
ones listed above. Reversing of the scales from high val-
ues to low values is permitted for analog input signals
that have a reversed action. For example, 50 psi = 4 mA
and 10 psi = 20 mA.
Select the low and high values with Process Scale
Low [SC;lo] and Process Scale High [SC;hi] (Setup
Page).
High Range and Low Range
With a process input, you must choose a value to
represent the low and high ends of the current or volt-
age range. Choosing these values allows the controller’s
display to be scaled into the actual working units of
measurement. For example, the analog input from a hu-
midity transmitter could represent 0 to 100 percent rel-
ative humidity as a process signal of 4 to 20 mA. Low
scale would be set to 0 to represent 4 mA and high scale
set to 100 to represent 20 mA. The indication on the dis-
play would then represent percent humidity and range
from 0 to 100 percent with an input of 4 to 20 mA.
Select the low and high values with Units Scale Low
[rg;Lo] and Units Scale High [rg;hi] (Setup Page).
Limits
Limit outputs are activated when the process value
or temperature goes above the high limit set point or be-
low the low limit set point. Limit outputs are always
latching. The operator must press the RESET Key or
cycle the input power to clear the limit condition once
the process has returned to a safe condition. Configure
limit outputs in the Setup Page before setting limit set
points.Output 1 is always a limit output.
Limit Sides
Limit outputs can have a low limit set point, high
limit set point or both low and high limit set points. For
example, if the application only requires high limit pro-
tection, select high side active
[high] for limit sides
[LSd1] (Setup Page).
Alarms
Alarms are activated when the process value or tem-
perature leaves a defined range. A user can configure
how and when an alarm is triggered, what action it
takes and whether it turns off automatically when the
alarm condition is over.
Configure alarm outputs in the Setup Page before
setting alarm set points.
Process Alarms
A process alarm uses one or two absolute set points
to define an alarm condition.
Enable the process alarm type with the Setup Page
parameters. View or change process alarm set points
with the Operations Page parameters.
Set Point Range (must be between Range High and Range Low)
Low Limit of selected Sensor Range
High Limit of selected Sensor Range
Temperature
Range High Range (between High Limit of Sensor and Range Low)
Range Low Range (between Low Limit of Sensor and Range High)
Range Low
Range High
Wa t l o w S e r i e s S D L i m i t ■ 4 2 ■ C h a p t e r 9 F e a t u r e s