Watlow Optimizing Your Process System with the Series 988 Controller - Manual (Page 46)

Optimizing Your Process System with the WATLOW Series 988
Standard Features
5.6
Input Errors
Overview
When the 988 receives input information it
cannot interpret or finds a problem with one of
its internal functions, it generates an error
code to help identify the problem. The control-
ler switches to manual mode and operates at a
fixed power output level, depending upon the
type of error code and the selections made in
the Global menu.
If an input related error occurs, four dashes
appear in the upper display and the
bottom display indicates the output power
level. Press the AUTO/MAN key once to display
the error code in the upper display for five
seconds.
The failure mode prompt determines what
the 988 output power level will be when an
input error occurs. The bumpless transfer
selection allows the 988 to switch from auto-
matic to manual mode at the percent power
level the controller was at when the input error
occurred. However, certain conditions must be
met: the process must have stabilized at a
power level between -70 percent and +70
percent, with no more than plus or minus five
percent variation for two minutes prior to the
sensor break. If these conditions have been
met, the 988 switches to manual mode at that
last stable power level. If not, the 988 transfers
to manual mode with no power output.
Preselect a power level at the failure mode
prompt
with the increment (up-arrow) and
decrement (down-arrow) keys. If the unit is
configured for heat only, the fail power level is
adjustable from 0 (off) to 100 percent (full
heat). If it controls heat and cool outputs, the
power level is adjustable from -100 (full cool) to
+100 percent (full heat).
If the error code is related to internal functions
of the 988 (
or ), the controller:
* remains in auto mode with both control
outputs off;
* switches all alarm outputs to the shelf state
(power OFF);
* lower display is blank and the upper display
indicates the error code;
* keys are all inactive.
The above conditions will occur regardless of
which menu is active at the time or what
failure mode value was selected. If
occurs,
all Setup menu parameters will return to
factory default values. To clear any one of these
errors, turn the 988 OFF for a few seconds
then turn it back ON. If the error remains,
contact the factory.
Series 988 error codes
input 1 input 2 A/D underflow error
input 1 input 2 sensor under-range error
input 1 input 2 sensor over-range error
input 1 input 2 A/D overflow error
non-volatile checksum error
configuration error
Sample Application
An engineer has many applications throughout his plant requiring con-
trollers. He wants to know what the controller will do if the sensor fails. In
some of his processes, for instance a gas valve, the outputs must go full
OFF (0 percent), others, such as a valve controlling water to a cooling
jacket, should go to full open (-100 percent), while others need the
outputs to go to an intermediate power level. With the 988 the user can
determine what the output will do if a sensor fails.