Watlow Series SD PID Profiling Controller - Manual (Page 68)

Wa t l o w S e r i e s S D • 6 6 • C h a p t e r 1 2 F e a t u r e s
High Scale and Low Scale
When an analog input is selected as process voltage or
process current input, you must choose the value of volt-
age or current to be the low and high ends. 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 are: 0 to 20 mA, 4 to 20 mA,
0 to 5V, 1 to 5V and 0 to 10V.
The Series SD allows you to create a scale range for
special applications other than the standard ones listed
above. Reversing of the scales from high values 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 mea-
surement. For example, the analog input from a humidity
transmitter could represent 0 to 100 percent relative hu-
midity 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 display 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).
Control Methods
Output Configuration
Each controller output can be configured as a heat
output, a cool output, an alarm output or deactivated. No
dependency limitations have been placed on the available
combinations. The outputs can be configured in any com-
bination. For instance, all three could be set to cool.
Analog outputs can be scaled for any desired current
range between 0 and 20 mA or voltage range between 0
to 10V. The ranges can be reversed to high-to-low for re-
verse acting devices.
Heat and cool outputs use the set point and Opera-
tions parameters to determine the output value. All heat
and cool outputs use the same set point value. Heat and
cool each have their own set of control parameters. All
heat outputs use the same set of heat control parameters
and all cool outputs use the same set of cool output pa-
rameters.
Each alarm output has its own set of configuration
parameters and set points, allowing independent opera-
tion.
Auto (closed loop) and Manual (open loop) Control
The controller has two basic modes of operation, auto
mode and manual mode. Auto mode allows the control-
ler to decide whether to perform closed loop control or to
follow the settings of the Input Error Failure Mode pa-
rameter (Setup Page). The manual mode only allows open
loop control. The Series SD controller is normally used in
the auto mode. The manual mode is usually only used for
specialty applications or for troubleshooting.
Manual mode is open loop control that allows the user
to directly set the power level to the controller’s output
load. No adjustments of the output power level occur
based on temperature or set point in this mode.
In auto mode, the controller monitors the input to
determine if closed loop control is possible. The controller
checks to make certain a functioning sensor is providing
a valid input signal. If a valid input signal is present, the
controller will perform closed loop control. Closed loop
control uses a process sensor to determine the difference
between the process value and the set point. Then the
controller applies power to a control output load to re-
duce that difference.
If a valid input signal is not present, the controller
will indicate an input error message [Er;In] and then
use the Input Error Failure Mode [FAIL] setting to de-
termine operation. You can choose to have the controller
perform a “bumpless” transfer, switch power to output a
preset manual level, or turn the output power off.
Bumpless transfer will allow the controller to transfer
to the manual mode using the last power value calculat-
ed in the auto mode if the process had stabilized at a ±5
percent output power level for two minutes prior to sen-
sor failure, and that power level is less than 75 percent.
Time
Te
mperature
40%
Sensor
Break
2 minutes Locks in
Output
Power
0%
Set Point Actual Temperature
Output Power
Power
100%
Input Error Latching [I;Err] (Setup Page) deter-
mines the controller’s response once a valid input signal
returns to the controller. If latching is on
[`Lat], then
the controller will continue to indicate an input error
until the error is cleared. To clear a latched alarm, press
the Infinity Key ˆ. If latching is off [nLAt], the control-
ler will automatically clear the input error and return
to reading the temperature. If the controller was in the
auto mode when the input error occurred, it will resume
closed loop control. If the controller was in manual mode
when the error occurred, the controller will remain in
open loop control.
The Auto-Manual Control Indicator Light % is on
when the static set point controller is in the manual