Watlow Optimizing Your Process System with the Series 988 Controller - Manual (Page 17)

Optimizing Your Process System with the WATLOW Series 988
Basic Control Strategies and Terms
2.7
condensing atmosphere, because the vented
case is susceptible to dripping water. If neces-
sary, include an enclosure heater in your
system to maintain the proper environment.
Is the front panel subject to spray or hose-
down conditions? (page 6.8)
• The Series 988 has a NEMA 4X-rated front
panel. This rating allows the controller to be
hosed down directly without damaging the
controller. Two gaskets protect the controller:
one seals the bezel of the control while the
other seals the controller face plate and the
panel cutout. When installing the controller be
sure that these gaskets are not twisted.
What are the agency requirements for the
controller and the system? (page 6.8)
• The Series 988 has a UL 873 and UL 508
recognition. CSA recognition is pending. Also,
the NEMA 4X rating was certified indepen-
dently by UL under UL 50X.
Controller Operation
Operation of the Series 988 can be broken
down into three concerns: setup; operation;
and maintenance. The questions you ask
yourself should examine each of these areas.
Does the system have any interactive process
variables? (Chapter 4)
• Interactive process variables include ratio,
differential or cascade control or slidewire
feedback of valve position. Also, heater current
measurements can be used to detect system
faults.
Is an event input useful in this application?
(page 3.6)
• Before finalizing the design check out this basic
option. The event input can expand the user-
friendliness and/or security of your system.
Is ramp to set point required? On start up?
On set point change? (page 3.10)
• Many systems are susceptible to damage if the
process changes too rapidly. The ramp to set
point feature can minimize system stress.
How should the controller respond to an
error? (page 5.6)
• In the event of an error, system response is
critical. Some systems might require that the
control output turn full ON to provide cooling.
Other systems would require that the control
outputs be turned OFF. The design of some
systems might allow the control to continue
operating in the manual mode without operator
action. All of these options are available with
the Series 988.
Are you shipping products overseas? (page 2.3)
• In some countries and in certain markets in the
U.S. the default units may be either degrees C
or degrees F and the PID parameters might use
proportional (in percent of span), integral and
derivative or proportional (in degrees), reset
and rate. The 988 can switch between these
default sets to suit the user's preference.
What level of operator security do you need?
(page 5.7)
• The Series 988 provides numerous levels of
both software and hardware lockout. Refer to
page 4.5 for more information on lockout.
What do you do if a system component fails?
(page 5.5)
• When investigating a system failure, the Series
988’s Diagnostics menu can be used to monitor
inputs and selectively activate outputs. The
menu also shows the software revision and the
I/O types.
What about field calibration?
• All Watlow microprocessor-based controls can
be field calibrated with the right equipment.
The calibration manual for the Series 988
family of controllers is available upon request.
Putting It All Together
You should now have a good idea of what types
of questions to ask when designing your system
with the Series 988. We suggest that you read
through the rest of this chapter and Chapters
Three through Seven for more detailed informa-
tion on the features available in the Series 988.
If you are already familiar with the 988, skip to
Chapter Seven to select the 988 that fits your
application.