Watlow Optimizing Your Process System User Manual

WATLOW
Optimizing Your Process System
with the Series 988 Controller
AN APPLICATION GUIDE
THE WATLOW
FOR
SERIES 988 FAMILY

Watlow Mission Statement

Industrial Heaters, Sensors and
Controls by Totally Satisfying Our
Customers with Superior Products,
Quick Delivery on Specials, as well as
Standards, and Intelligent Sales
Support.
Copyright Watlow Winona, Inc., © 1994, with all rights reserved.

Introduction

Welcome to the Watlow Series 988 application guide: Optimizing Your Process System with the WATLOW Series 988. This application guide describes all the
features of the Series 988 and how they can be applied to your system. In addition, this guide will walk you through the process of determining the op­timal Series 988 for your application. Once you have purchased the control­ler, the Series 988 Users Manual will guide you through installation and setup of the controller.
Start with Chapter One of this book, where “test drives” show the thought process used for determining the correct Series 988 feature set for a specific application. Chapter Two consists of a glossary and a question-and-answer section that provides more details to help choose the right control. Chapters Three through Five describe the features of the controller with a sample appli­cation for each feature. Chapter Six outlines the controllers’ specifications. Use this chapter to ensure that the controller interfaces correctly with other system components. Finally, Chapter Seven walks you through the feature set selection for your specific application. Once you have used the guide a few times, you will be able to skip to Chapter Seven and use the previous chapters for reference.
The purpose of this technical guide is to assist you in the system design pro­cess. The final responsibility for the system design must remain with the sys­tem design engineer.
Watlow manufactures heaters, sensors and controls. We can provide a com­plete thermal system. For more information concerning the Series 988, con­tact your local sales representative listed on the back cover. Literature on the Series 988 includes:
Series 988/989 Users Manual
Calibrating Watlow Process Controls
How to Use Data Communications with the Watlow Series 988/989 or How to Use Data Communications with the Watlow Process Controls

Disclaimer of Warranty

The information presented here is of a general nature. Because of the diver­sity of conditions and hazards under which control products may be applied and because of the differences in components and methods of installation, representation or warranty of any kind, express or implied, is hereby made, that the applications discussed herein will be effective in any particular appli­cation or set of circumstances, or that additional or different precautions will not be reasonably necessary for a particular application.
no
We will be pleased to consult with you regarding a specific application, upon request.
Table of Contents

Table of Contents

Watlow Mission
Introduction
Chapter 1 Test Drives 1.1
Controlling an Extruder 1.2 Drying Grain 1.4 Melting Aluminum 1.6 Mixing Urethane 1.8
Chapter 2 Basic Control Strategies and Terms 2.1
Glossary 2.2 Questions and Answers 2.5 Control Strategies 2.8
Chapter 3 General Software Features 3.1
Auto-tune 3.2 Burst fire 3.3 Communications 3.4 Dead band 3.5 Digital event 3.6 Heater current 3.7 Input filter 3.8 Input linearization 3.9 Ramp to set point 3.10 Remote set point 3.11 Retransmit (master/remote) 3.12 Slidewire feedback 3.13
Chapter 4 Enhanced Software Features 4.1
Cascade 4.2 Differential 4.4 Dual PID sets 4.5 Duplex 4.6 Ratio 4.7
Optimizing Your Process System with the WATLOW Series 988
Table of Contents
Chapter 5 Standard Features 5.1
Alarms 5.2 Auto/Manual 5.4 Diagnostics 5.5 Input errors 5.6 Lockout 5.7 Transmitter power supply 5.8
Chapter 6 Specifications 6.1
Input Table 6.2 Output Table 6.3 Dimensions 6.4 Displays and Keys Chart 6.5 Setup Requirements 6.6 User's Manual 6.7 Product Specifications 6.8 Warranty 6.9
Chapter 7 Select the 988 That Fits Your Application 7.1
Overview 7.2 Input 7.3 Output 7.4 Software 7.5 Standard Features 7.6 Hardware 7.7 Review and Optimize 7.8 Application Worksheet 7.10 Series 988 Model Number Worksheet 7.11
Index 8.1
Prompts, parameters and menus 8.4
Watlow Sales Offices back cover
Optimizing Your Process System with the WATLOW Series 988
Test Drives
Chapter One
Test Drives
Controlling an Extruder 1.2 Drying Grain 1.4 Melting Aluminum 1.6 Mixing Urethane 1.8
How to use this chapter:
This chapter describes four actual appli­cations in which processes are optimized by using Watlow Series 988 controllers.
Optimizing Your Process System with the WATLOW Series 988
1.1
Basic Control Strategies and Terms
Chapter Two
Basic Control Strategies and Terms
Control Strategies 2.2 Questions and Answers 2.5 Glossary 2.8
How to use this chapter:
This chapter explains control terms and strategies, especially as they apply to the Watlow Series 988 family of controllers. It will help you identify issues specific to your application, and allow you to imple­ment the Series 988 controller in the most cost effective manner, giving you optimal control of your specific system.
Many of the decisions for system compo­nents are limited by factors not associ­ated with the Series 988. The strategy presented here is designed to get you thinking of all the different parameters associated with your system and how the Series 988 fits in.
Optimizing Your Process System with the WATLOW Series 988
2.1
Basic Control Strategies and Terms

Control Strategies

Process Control
Process controls are of two basic types: open loop and closed-loop. An open-loop control device has no self-correcting feedback informa­tion. The closed loop system uses feedback information from a sensor to adjust the system. As the process changes, the feedback loop provides up-to-date status information that the controlling device uses to make self-correcting adjustments. The closed-loop control device provides much better process control.
Control Modes
A variety of control modes offer various degrees of controllability. The most common modes are on-off and PID control. The PID control cat­egory includes varying degrees of complexity that provide accurate, stable control under a variety of conditions.
ON/OFF Control
The operation of the ON/OFF control, as the name implies, turns the output device full ON or full OFF. Temperature or process sensitivity (hysterisis) is designed into the control action between the ON and OFF switching points to prevent switching the output device ON and OFF within a span that is too narrow. Switch­ing repeatedly within such a narrow span will create a condition of intermittent, rapid switch­ing, known as output “chattering.” The process is always controlled “about set point,” dictated by the switching hysterisis of the ON/OFF control. This form of control action further dictates that there will always be a certain amount of overshoot and undershoot. The
degree of overshoot and undershoot will be dependent on the characteristics of the entire system.
Time Proportioning
Time-proportioning control provides more precise control of a process. A time-proportion­ing control operates in the same way as an ON/ OFF control, when the process is far enough away from set point to be outside the propor­tional band. When the process approaches set point and enters the proportional band, the output device is switched ON and OFF at the established cycle time. At the lower limit of the band, the ON time is considerably greater than the off time. As the process more closely approaches set point, the ratio of ON to OFF time changes: the amount of ON time decreases as the OFF time increases. This change in effective power to the load provides a throttling­back effect, resulting in less overshoot.
The ON and OFF cyclic action continues until a stable relationship is achieved. At that time, the system will be stabilized such that the
Time Proportioning
Temperature
Set Point
Proportional
Band
Overshoot
Droop
On - Off
Switching Sensitivity
Temperature
Set Point
Time
Profile produced by ON-OFF control
Optimizing Your Process System with the WATLOW Series 9882.2
Time
Profile developed by proportioning control
process is controlled at a point below set point. The process stabilizes with a resultant droop. This condition will remain providing there are no work-load changes in the system.
Integral
If the droop cannot be tolerated, there are ways to compensate for it. Integral (automatic reset) is an automatic adjustment to compensate for
Basic Control Strategies and Terms
a droop condition before it exists. An integra­tion function takes place that automatically compensates for the difference between set point and the actual process. This integration automatically drives the process toward set point. Integration action is prevented until the process enters the proportional band. If it was
Time Proportioning
With Automatic Reset
Proportional
Temperature
Set Point
Profile developed by a proportional plus integral control
Band
Overshoot
Droop
Time
allowed to take place at any point, it would cause a condition of extreme overshoot. This function of eliminating the integration outside of the proportional band is referred to as “anti­reset windup.”
Derivative
As all of the graphs have illustrated, overshoot occurs with any of the previous control meth­ods. Overshoot may be hazardous to certain processes. It is preventable with a control function known as “derivative” (rate).
Derivative is an anticipatory function in a process control that measures the rate of change of the process and forces the control into a proportioning action on an accelerated basis to slow that change. This action prevents a large degree of overshoot on start-up and also functions to prevent overshoot when system disturbances would tend to drive the process up or down. A proportioning control with integral and derivative (PID) control provides the type of control required for difficult pro­cesses with frequent system disturbances or applications that need precision control.
PID -Time Proportioning
With Auto Reset & Rate
Proportional
Temperature
Set Point
Profile developed by a proportional plus integral plus derivative (PID) control
Band
Reduced Overshoot
Time
Control System Tuning
In this phase of making the system work, we will focus on the process controller as the primary component of a closed-loop system that must be adjusted for optimum perfor­mance. These adjustments provide a means to compensate for system problems. For instance, when the sensor cannot be placed in the most desirable location because of physical limita­tions, a PID controller can compensate for the sensor’s resulting thermal lag problem.
Tuning Methods
Process controls are tuned manually or auto­matically. Manual tuning requires manually setting each of the controller’s operating pa­rameters. Automatic tuning, or auto-tuning, is accomplished by the 988’s digital, microproces­sor-based, electronic circuitry. The controller uses a program inside its memory that will calculate the correct setting for each of the controller parameters. For more information on auto-tuning with the Series 988 refer to page
3.2.
Manual Tuning
The following steps are generally applicable to most manually set process controllers. Please take note of a few precautions:
• Take your time in tuning the control system. If you do it right, it will work a long time without further attention.
• Do not change more than one control adjust­ment at a time, allowing the system to settle
Optimizing Your Process System with the WATLOW Series 988
2.3
Basic Control Strategies and Terms
down to a state of equilibrium before making another change.
• Remember that the time you need to spend tuning the electronic controller system is relative to the precision of control you need.
Proportional Band
The proportional band adjustment is the means of selecting the response speed (gain) or sensi­tivity of a proportioned controller to achieve stability in the system. The proportional band — whether measured in degrees, percent of range or other units — must be wider than the natural oscillations of the system and yet not wide enough to dampen the system response. The time proportioning output must be set to switch faster than the natural oscillation of the system, sometimes called, “system cycle time.” The tuning procedure is very simple, if you can use a recorder to monitor the actual process variable. If a recorder is not available, observe the process response and record readings over a defined time period.
If the system oscillates when the proportional band is at its narrowest setting (not zero), the adjustment of the proportional band should be increased in small increments until the oscilla­tion stops. Because the proportional band has been tuned (adjusted) to have the controller seek stability of the system, very often an offset (droop) from the set point occurs. At this point in tuning the system, the process variable should be in a state of equilibrium, but not right on the desired set point.
Integral (Reset)
The reset adjustment is tuned at this point to correct for the droop caused by the propor­tional output. While it does automatically correct for offset errors, automatic reset has to be tuned to each system. Each system has its own characteristic response time (system cycle time), thus, the auto reset time constant (repeats per minute) must be tuned to match the overall system response time.
small increments, allowing the system to settle down (stabilize) before making additional changes, until the system just starts to oscil­late. Then back the setting off enough to re­establish system equilibrium.
Derivative (Rate)
Rate is the last control parameter adjustment to be made. Rate’s function is to reduce or eliminate overshoot (excursions above or below set point). It has a time base (measured in minutes) that must be tuned to work with the overall system response time (system cycle time). The initial setting for rate should be at the smallest integer of minutes possible (least corrective action). Increase the integer in small increment, then after each adjustment increase the set point moderately. Observe the approach of the actual process to set point. If it over­shoots, continue to increase the rate integer in small increments. Then increase the set point moderately until optimum approach to set point is achieved. If at some point the system becomes very sluggish or cannot reach the new set point at all, too much rate (corrective action) has been adjusted into the control system. To reduce this “damping” effect, decrease the number of minutes of rate.
Recommended Tuning Reference
There are many reference books on the art of tuning electronic controllers to the systems they control. If you are not an instrument technician qualified to tune thermal systems, we suggest that you become familiar with the following reference before attempting to tune your system:
Tuning of Industrial Control Systems
by Armando B. Corripio Published by the Instrument Society of America (ISA) Member $48.00, list $60.00 (approx.). Phone: (919) 549-8411
Initially auto reset should be set at the lowest number of repeats per minute (least corrective action). Increase the repeats per minute in
Optimizing Your Process System with the WATLOW Series 9882.4
Basic Control Strategies and Terms

Questions and Answers

System Diagram
No matter what your application, you must start with an accurate system diagram. A blueprint of the system wiring is typically not a faxable document. When consulting the factory, it’s helpful to be able to fax a system diagram similar to the hand drawings shown in the Test Drives in Chapter One. This diagram should include all inputs, outputs, the controller, the load, any alarms and any connections to other systems or equipment. This diagram should show the expected signal types and ranges at each interface point to allow you to properly order and set up your 988 controller. For the advanced user of the Series 988 this will be second nature. For the less experienced opera­tor, putting together a diagram including all system components will allow a Watlow sales rep or factory applications engineer to review the system for correctness.
Inputs
The 988 controller accepts a wide variety of input signals and ranges, covering most tem­perature and process applications. Ask yourself the following questions about your inputs:
What accuracy is required for each input?
(page 6.8)
• RTD’s will provide the most accurate measure­ment in a temperature-related system.
• The accuracy of a process sensor for flow, level, pressure, etc. will depend strictly on the sensor manufacturers specifications.
• The Series 988 measures the input and updates the output 10 times per second with one input. With 2 inputs, each input is measured five times per second.
What is the wire length required to reach controller? (page 6.8)
• When designing a system using thermocouple or RTD sensors, if the lead length is excessive, errors may be introduced into the system. By using a signal transmitter to convert the thermocouple or RTD signal to a process signal the errors can be avoided.
RTD sensor. However, it almost never pays to spend less on a sensor, which is arguably the most important part of the thermal system.
• Process sensors can vary widely in cost. Other factors, such as accuracy, response time and durability, must be weighed.
Will this be a grounded or ungrounded applica­tion? (page 5.8)
• Although inputs are electrically isolated from outputs in the 988, you must determine if other sources of ground loops in the system may affect the sensor. This can occur, in the Series 988, if there are two grounded inputs or if an output is tied to an input, such as using a transmitter power supply output to power a thermocouple transmitter.
Is the process relatively fixed or widely vary­ing — what is the range? (page 6.8)
• Make sure you check (and re-check) the ranges of the input options available in the 988. Although the 988 can operate outside the ANSI ranges for specific thermocouples and RTD’s, it is not recommended and will shorten the life of the sensor.
Are there concerns over electrical noise immunity?
• Although the Series 988 is thoroughly tested for electrical noise immunity, it is paramount that you follow good engineering practices when designing the placement of the sensor and power wires. Refer to the Series 988 Users Manual and the Watlow Catalog.
Outputs
The outputs command the system to heat, cool, turn ON and OFF, and also trigger other actions in this system or related systems.
It is very important that you maintain total control over the process. External limits or other devices to disable the outputs can protect system components and provide an added layer of safety. Consider the following:
Is cost a factor in the sensor selection?
• Typically, a thermocouple costs less than an
Optimizing Your Process System with the WATLOW Series 988
How frequently will the output need to cycle to control the process? (page 6.8)
2.5
Basic Control Strategies and Terms
• What is frequent? In order to tightly control a process, the more frequent the better. Unless absolutely necessary, mechanical relays should not be used as the control output. A typical mechanical relay application cycles ON and OFF 86,400 times over a period of one month (30 second cycle time, 24 hours per day). The mechanical relay option is only warranted for 100,000 cycles.
• With a solid-state output a variable-time-base burst fire option can provide the tightest load control. Make sure the power control is com­patible with the burst-fire output. (page 3.3)
What actuator interfaces are required? (page
6.8)
• Typically the output of the Series 988 does not directly control the load. Instead it acts as a pilot-duty output interfacing with another device that actually controls the load. If this is the case in your application, make sure that the output of the Series 988 is compatible with the input of the external device.
What alarm or annunciation outputs are required? (page 5.1)
• The alarm options in the Series 988 can be used to alert an operator to a system malfunc­tion. These outputs should not be used as safety limits to protect system components or personnel. A separate safety limit device should be used in any system where damage or injury could occur due to a system component failure.
How should the alarms operate? (page 5.1)
• The alarm options can be field-configured to function in any fashion. A process alarm can be used to warn the operator of impending equipment damage. A deviation alarm can be used to warn that the system is operating outside of the desired specifications. Each alarm can be set for latching or non-latching, silencing and reverse or normal logic.
process output (4-20mA, 0-5VDC, etc.). Also, it limits the minimum on-time of the output.
Does the process require a retransmit output?
(page 3.12)
• Output 3 can be used as either a 4-20 or 0­20mA output or as a 0-5, 1-5 or 0-10VDC output to retransmit the process value of either of the inputs or the set point value. It allows the controller to function as a master controller in a master-remote application or to retransmit a process value to a chart recorder.
What types of monitoring of the outputs is required? (page 3.4)
• The retransmit option is one way to monitor the system status.
• A serial communications option can be used to monitor and/or change all the parameters in the controller. With the EIA-485 option up to 32 controllers can be monitored from a single communications port on a personal computer, over distances of 4000 feet. The RS-422 option can address up to 10 controllers over 4000 feet, and the RS-232 option can address a single control over a distance of 50 feet. Make sure the computer or other monitoring device is equipped with the correct serial communica­tions card and that the baud rate and other capabilities are compatable.
Controller Environment
There are several factors to consider concern­ing the environment that the Series 988 con­troller operates in:
What are the physical dimensions of the enclosure? (page 6.4)
• The Series 988 family of controls has a behind­panel depth of 4.06 inches, allowing the control to fit an enclosure with a depth of 6.0 inches. When mounting more than one controller in a panel we recommend a minimum spacing of
1.66 inches between controllers.
Should you monitor the load current? (page
3.7)
• While this option is available as an input, it is important to note that this feature in the Series 988 is not currently available when using a
Optimizing Your Process System with the WATLOW Series 9882.6
What is the ambient temperature inside the enclosure? (page 6.8)
• The Series 988 can operate in ambient tem­peratures as low as 32°F (0°C) and as high as 150°F (65°C). The enclosure requires a non-
Basic Control Strategies and Terms
condensing atmosphere, because the vented case is susceptible to dripping water. If neces­sary, include an enclosure heater in your system to maintain the proper environment.
Is the front panel subject to spray or hose­down 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 indepen­dently 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 user­friendliness 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 informa­tion 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.
Optimizing Your Process System with the WATLOW Series 988
2.7
Basic Control Strategies and Terms

Glossary

annunciator — a device that uses pilot lamps to
indicate the former or existing condition of a system being monitored.
ANSI — American National Standards Institute.
burst fire — output that switches full AC cycles
ON and OFF repeatedly. Zero-cross burst fire switches only at the zero-voltage point of the AC sine wave. Variable-time-base burst fire would switch ON and OFF 30 times a second to achieve a 50-percent power level with a 60­cycle AC power supply. Also see “zero switch­ing.”
calibration offset — adjustment to the actual
process input and to the process values the Series 988 uses for display and control.
cascade — control algorithm in which the output
of an outer control loop is the set point for an inner loop. The inner loop, in turn, determines the control action.
closed loop — control system that uses a sens-
ing device for process variable feedback.
derivative — anticipatory action that senses the
rate of change of the process, and compensates to minimize overshoot and undershoot. Also see “rate.”
differential control — With enhanced software,
the Series 988 controller can control one process in relation to the difference of a second process. A set point is added to the measured value of the second process. This sum is used as the set point for the input 1 process value.
DIN — Deutsche Industrial Norms, a widely
recognized German standard for engineering units.
droop — difference between the set point and
stabilized process value.
duplex control — With enhanced software,
duplex control splits a single process output into two individual outputs. For example, a 4­20mA output is split into a 4-12mA direct acting (cooling) output and a 12-20mA reverse acting (heating) output, thus allowing one control output to function as two.
cold junction — point of connection between
thermocouple metals and the electronic instru­ment.
cold junction compensation — electronic
means to compensate for the effective tempera­ture at the cold junction.
current transformer — a transformer, designed
for measuring electrical current, with its primary winding connected in series with a circuit carrying the current to be measured.
dead band — The dead band setting determines
the amount of interaction between heat (reverse acting) and cool (direct acting) control outputs.
default parameters — the parameters, or pro-
grammed instructions, permanently stored in the microprocessor software.
Optimizing Your Process System with the WATLOW Series 9882.8
duty cycle — percentage of load-ON time relative
to total-cycle time.
external transmitter power supply — a DC
voltage source of power for external devices.
filter — as applied to the Series 988, a low-pass
filter designed to minimize display or process input fluctuations.
form A — single-pole, single-throw relay that
only utilizes the normally open (N.O.) and common contacts. These contacts close when the relay coil is energized. The contacts open when power is removed from the coil.
form B — single-pole, single-throw relay that
only utilizes the normally closed (N.C.) and common contacts. These contacts will open when the relay coil is energized. The contacts will close when power is removed from the coil.
Basic Control Strategies and Terms
form C — single-pole, double-throw relay that
utilizes the normally open (N.O.), normally closed (N.C.) and common contacts. The user has the option of wiring for a form A or form B contact. Refer to the form A and form B above for more information.
hunting — oscillation or fluctuation of the
process between the set point and process variable.
hysteresis — in ON/OFF control, the process
change necessary to change the output from full on to full off.
input linearization — For thermocouple and
RTD inputs, the process variable is automati­cally linearized. Certain flow transmitters generate a non-linear signal corresponding to the flow being measured. The square root of the signal is calculated to generate a linear signal.
integral — control action that automatically
eliminates the offset, or “droop,” between the set point and actual process value. Also see “reset.”
isolation — Electrical separation of sensor from
high voltage circuitry. Allows use of grounded or ungrounded sensing element.
JIS — Joint Industrial Standards. Also Japanese
Industrial Standards Committee (JISC). Estab­lishes standards for equipment and compo­nents.
open loop — control system without sensory
feedback.
output — action in response to difference be-
tween the set point and process variable.
overshoot — condition in which the process
exceeds set point due to initial power up or process changes.
P control — proportioning control.
PD control — proportioning control with deriva-
tive (rate) action.
PDR control — proportional derivative control
with manual reset is used in fast responding systems where the reset causes instabilities. With PDR control, an operator can enter a manual reset value that will eliminate any droop in the system. The option requires enhanced software.
PI control — proportioning control with integral
(auto-reset) action.
PID control — proportioning control with inte-
gral (auto-reset) and derivative (rate) action.
process variable — regulated system parameter,
such as time, temperature, flow, humidity, etc.
proportional band — span of the process from
the set point within which time proportional control action takes place.
linearization — the extraction of a linear signal
from the non-linear signal of a flow transmitter. Also see “input linearization.”
NEMA 4X — a front-panel rating that certifies
the control as washdown capable and corrosion resistant.
ON/OFF control — control of a process by
turning the output full ON below set point and full off above set point.
Optimizing Your Process System with the WATLOW Series 988
proportioning control — See "time proportion-
ing control."
rate band
where the rate (derivative) function begins. The Series 988 rate band centers on the set point and is twice the width of the proportional band.
ratio — application in which the flow of an
uncontrolled stream is measured and used to maintain the flow of a controlled stream at a ratio to the uncontrolled stream.
a thermal control band that defines
2.9
Basic Control Strategies and Terms
reference junction — synonymous with cold
junction. Also see “cold junction.”
retransmit — an analog signal representing a
control variable, either the process values or the set point values.
RTD — resistance temperature detector. Resistive
temperature-sensing device that displays a positive temperature coefficient.
slidewire feedback — closed-loop, valve-actuator
control using a potentiometer to indicate valve position.
switching sensitivity — in ON/OFF control, the
process value change necessary to change the output from full on to full off.
thermal system — a regulated environment
consisting of a heat source, heat transfer medium, sensing device and a process variable control instrument.
thermocouple — temperature-sensing device
constructed of two dissimilar metals that generates a measurable, predictable voltage that corresponds to its temperature.
supply power to external signal conditioners, transducers or transmitters. With internal DIP switches, the user selects between 5, 12 or 20VDC at 30mA ratings.
zero-cross — Action that provides output switch-
ing only at the zero-voltage crossing points of the AC sine wave. Also see “burst fire.”
thermocouple break protection — fail-safe
operation that assures output shutdown upon an open thermocouple condition.
three-mode control — proportioning control
with integral (reset) and derivative (rate). Also see “PID.”
time proportioning control — action that varies
the amount of on and off time when “close” to the set point, i.e., in the proportional band. This variance is proportional to the difference between the set point and the actual process. In other words, the amount of time the output relay is energized depends on the system process value.
transmitter power supply — When Option “T” is
ordered for output 2, 3 or 4, the Series 988 can
Optimizing Your Process System with the WATLOW Series 9882.10
General Software Features
Chapter Three
General Software Features
Auto-tune 3.2 Burst fire 3.3 Communications 3.4 Dead band 3.5 Digital event 3.6 Heater current 3.7 Input filter 3.8 Input linearization 3.9 Ramp to set point 3.10 Remote set point 3.11 Retransmit (master/remote) 3.12 Slidewire feedback 3.13
How to use this chapter:
This chapter describes the software features that are available in Watlow Series 988 controllers. Enhanced soft­ware options provide additional features that are described in Chapter Four.
3.1Optimizing Your Process System with the WATLOW Series 988
General Software Features
TL
Overview:
The auto-tune feature allows the controller to manipulate the process and calculate PID values based on the process response. This relieves the operator from the tedious task of manually tuning the PID parameters to match the characteristics of the thermal system.

Auto-tune

During an auto-tune the controller monitors how fast the process increases and decreases, and from this information calculates propor­tional band, reset and rate values and auto­matically enters them into non-volatile memory.
The point at which the auto-tune takes place is determined by the auto-tune set point parameter. It is adjustable from 50 percent to 150 percent of the current set point, with 90 percent being the factory default setting. If the auto-tune set point is 90 and the current setpoint is 300 degrees, the control goes into ON/OFF mode of control at 270 degrees (300 deg. x 0.9). The displayed setpoint is un­changed and the bottom display information alternates with tune
at a one-second rate until the auto-tune is completed. Any changes to the set point during an auto-tune will cause the auto-tune sequence to start over, based on the new set point.
To abort an auto-tune, set the auto-tune prompt
to or press the AUTO/MAN key twice, or cycle the power OFF and ON. The previous PID parameters will be restored.
Requirements
The Series 988 can be ordered with two com­plete sets of heat/cool PID sets. This requires the enhanced software option. A single set of PID parameters is available with the standard software option.
350°
315°
auto-tune complete
temperature
time
Oven
heater
input 1
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MODE
W
MAN
output 1
limit
limit sensor
Sample Application:
In this example the oven needs to hold at 350 degrees F. To complete the tuning sequence set the set point for 350 degrees and auto-tune by setting the auto-tune prompt to
3.2
Optimizing Your Process System with the WATLOW Series 988
.
temperature sensor
General Software Features
TL
Overview
Variable, time-base burst firing from the 988 provides a command signal to an SSR or SCR firing card that translates into a burst of AC cycles. The output is zero-cross fired and always allows at least one AC cycle to pass within the variable time base. The fact that we are zero-cross switching the power device means we enjoy the benefits of low radio frequency (RFI) noise. Burst firing is the pre­ferred mode to control resistive loads.
The burst fire time base in the 988 varies from a maximum 1.66-second time base (1-percent output) down to a 33.3-millisecond time base (50-percent output). The examples below show how the time base varies depending on the percent output.

Burst Fire

Requirements
The 988 family has built in zero-cross detection circuitry. Therefore special firing circuitry is normally not required for triggering SCR’s. To enable burst fire the 988 must have an open collector or solid-state relay output. The feature is enabled by selecting burst fire cycle time prompt for the appropriate output.
You should note that the short time bases used by burst fire makes it incompatible with the heater current feature (see page 3.7). The heater current option requires a minimum of 300 msec. ON-time to get a reading.
Only the 988 and 989 can use the burst fire feature. cannot use burst firing.
at the
The low-voltage units (986 and 987)
50% Output100% Output
10 ON, 0 OFF 1 ON, 1 0FF
10% Output
1 ON, 9 OFF 2 ON, 1 OFF
input 1
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
W
DISPLAY
AUTO
MAN
MODE
output 1
QPAC
with
QCD
input
66% Output
Semiconductor Oven
limit
limit sensor
Sample Application
The 988 is being used to control a heated platen in a semiconductor oven. Previously it required a power control requiring a 4-20mA signal to implement burst-fire control. We have replaced the power control with a Watlow Loyola QPAC with a QCD card that accepts a signal directly from an open-collector output of the 988. This gives smooth control at a lower overall system cost.
temperature sensor
heated platen
3.3Optimizing Your Process System with the WATLOW Series 988
General Software Features
TL
TL
TL
TL
TL

Communications

Overview
The serial communications feature allows the Series 988 family to receive commands from and transmit data to a master device, usually a computer. Any function that can be performed via the front panel, can also be accomplished using the serial communications port, allowing you to operate the controller from a computer and to store process data on a computer.
The 988 is available with a choice of serial hardware interfaces. An RS-232 interface allows for one master (computer) and one controller, with a maximum network length of 50 feet (15 meters).
The EIA-485/RS-422 option equips the control­ler for a multi-drop interface: up to 32 total network devices with EIA-485 and up to 10 total network devices with RS-422. Each controller will have its own unique address. The total maximum network length is 4,000 feet (1,219 meters). These are isolated inter­faces.
To select between EIA-485 or RS-422, enter the setup prompts by holding the increment (up­arrow) and decrement (down-arrow) keys simultaneously until setup
appears in the bottom display. Use the decrement key to select the Communications menu prompt
selects between 485 or 422.
. The interface
Other parameters that must be configured in the Communications menu rate
, data bits and parity , protocol
are the baud
, and device address . The protocol
prompt must be set to full (ANSI X3.28 2.2-A3) if multiple devices are used with the EIA-485 or RS-422 interface. If the full protocol is selected, a device address must be selected at the address prompt 232, full
or on (XON/XOFF) protocol
. For RS-
may be selected.
Requirements
Choose which interface your application will use: RS-232 serial communications; EIA-485; or RS-422 serial communications. The com­puter must have a compatible serial port.
Personal Computer
with RS-422 port
Test
Chamber 1
W A TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO
MAN
MODE
SERIES 988
Test
Chamber 2
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO MAN
MODE
SERIES 988
Test
Chamber 3
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO MAN
MODE
SERIES 988
Test
Chamber 4
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO MAN
MODE
SERIES 988
output 4 output 4 output 4 output 4 output 4
Sample Application
A test engineer uses 988’s to control the temperatures of several automated test chambers. His computer is linked to the controllers through its RS-422 serial communications port. His computer program monitors the tempera­tures of the 988’s and initiates automatic test sequences when certain pro­gram parameters have been met. After completing a sequence, the computer loads the next temperature to the controller. The computer periodically interrogates each controller for its process temperature, set point and alarm status. This information is stored on a disk to provide test verification data for the completed products.
3.4
Optimizing Your Process System with the WATLOW Series 988
Test
Chamber 5
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO MAN
MODE
SERIES 988
General Software Features
TL

Dead band

Overview
The dead band prompts, located in the PID menus, determine the amount of interaction between heat (reverse acting) and cool (direct acting) control outputs. The dead band directly offsets the target set point of the cool control output.
With a positive dead band, both control out­puts will never be on at the same time. With the process in a positive dead band, the output value is determined by adding the percent heat output to the percent cool output and only applying the result to the correct output — cooling action if the sum is negative and heating action if it is positive.
and ,
If the dead band is set to a negative value, the heat and cool outputs can both be ON at the same time.
Requirements
The dead band feature is standard on any Series 988 controller with two control outputs. The dead band prompts will appear if the control outputs are configured for heat/cool or cool/heat.
Environmental Chamber
W
A
TL
input 1
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
output 2
limit
chiller
limit sensor
heater
Sample Application
An engineer for an environmental chamber manufacturer, who is design­ing the heating and cooling system for a new chamber, wants to minimize the energy costs of operating the chamber. She has chosen the 988 and will configure the heat and cool outputs with a positive dead band.
When the chamber temperature is near ambient the cooling and heating systems had a tendency to buck one another, resulting in inefficient use of energy. The engineer started with a dead band of five degrees, but in the process of tuning the system for optimal control, the setting was reduced to two degrees. This made the system more energy efficient and reduced wear on the refrigeration system.
temperature sensor
3.5Optimizing Your Process System with the WATLOW Series 988
General Software Features
TL

Digital Event

Overview
The digital event input options on the Series 988 controller allow the operator to select one of several software functions with the close of a customer-supplied switch or by a change in DC voltage.
The list below outlines the functions that can be controlled with the digital event input.
Idle set point with the close of a switch, a second (idle) set point. Turn control outputs OFF closed input to inhibit the control outputs. Alarm reset
lets the operator select,
allows a
resets alarms from a remote
location with a momentary closed input. Switch PID sets
selects between PID set
A or B (requires enhanced software). Remote set point
switches between local
and remote set points. Front panel lockout
locks out the front
panel keys to prevent tampering. Control output action
switches the control action of Output 1 from heating to cooling, or vise versa.
Requirements
A single digital event input is standard on all controls. A second digital input is available as an option for Input 2.
Incubator
W
A
TL
input 1 output 1
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO
MAN
MODE
SERIES 988
input 3
(event input 1)
switch
limit
limit sensor
heater
Sample Application
A manufacturing engineer is building an application that needs to switch to an idle temperature at the end of a batch and maintain that temperature until the next batch is loaded, with minimum operator interaction.
By connecting an external switch to the digital event input, he can select either the operating temperature or the idle temperature with the flip of a switch. The idle set point prompt is enabled by setting the event input 1 prompt
, in the Global menu, to the idle set point . The idle set point value is accessed by pressing the MODE key from anywhere in the display loop. When the switch closes, the lower display will indicate the idle set point, and the controller will maintain this new set point.
temperature sensor
3.6
Optimizing Your Process System with the WATLOW Series 988
General Software Features
TL

Heater Current

Overview
The heater current feature measures and responds to heater current in a system. This is an ideal method for detecting heater loss in multiple heater applications. The current is measured when output 1 is ON. For instance, if a system has five, 10-amp heaters, the heater current input measures 50 amps regardless of the percent output.
To view the heater current press the DISPLAY key and advance to the process 2 prompt The upper display indicates the last valid current reading.
The input 2 prompt menu error detect
can be set to current or loop
. Current allows you to monitor heater current and set alarm set points based on high and low heater current values. Alarms can only be configured as process alarms (see Alarms, page 5.2). Setting to loop error detect and alarm functions, and also triggers an error and shuts OFF all outputs if current is present with output 1 OFF or when no current is present and output 1 power is more than zero.
under the Input
enables monitoring
There are limits associated with this feature:
To obtain a reading, the output ON-time must
be a minimum of 0.3 seconds. To calculate this, multiply the percent output by the cycle time setting. Example: With 30-percent output and a 2.0 second cycle time, the on-time would be: 0.30 x 2.0 = 0.6 seconds. This would yield a valid reading. If a valid reading is not possible, the 988 will display the last valid reading.
It will not function with burst-fire outputs. This
.
does not necessarily apply to the loop error detect feature. If enabled, any current detected with no output triggers an error.
It will not function when the 988 has a process
output for output 1. A known cycle time is required to detect the current. There is no cycle time associated with process outputs.
The maximum signal the input can accept from the current transformer secondary is 50mA. So, you must calculate the output range of the current transformer before wiring the system.
Requirements
Choose the heater current option for input 2. Output 1 cannot be used as a process output. Heater current monitors only output 1.
input 1
input 2
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
current transformer
limit
Compression Molding Press
limit sensor
10A heaters
temperature sensor
W
A
TL
Sample Application
The Series 988 controls the lower platen of a compression molding press that contains five, 10­ampere heaters. A 50A:50mA current transformer is used to monitor heater current. Set the input 2 prompt prompt
range high 2 =
The application uses a Watlow current transformer (CT) part# 16-0233, which has a maximum input of 50 amperes, which corre­sponds to a maximum output of 50mA.
range high 2 =
(maximum output from CT secondary (input))
50mA
to 50. Find the range high 2 value with the following equation:
(maximum CT primary current (load current))
(50Amps)
x 50mA
to current , the range low 2 prompt to 0 and the range high 2
x 50mA
Solving for rH2 gives you 50. This is the range high 2 setting.
3.7Optimizing Your Process System with the WATLOW Series 988
General Software Features
Overview
In certain applications the process being measured can be unstable, which makes it difficult to control and also makes the con­stantly changing display difficult to read. The Series 988 input filter can solve these problems by smoothing out just the display or the display and the input signal.
You can set a time constant, in seconds, for a

Input Filter

low-pass filter that will affect the display only, or you can configure the option to filter the input signal itself. Use this feature with cau­tion, because a large time constant could hide system upsets.
Requirements
This feature is standard on all Series 988 controllers.
input 1
input 2
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
W
DISPLAY
AUTO
MAN
MODE
Display readings with input filter off
%RH
output 1
limit
Display readings with input filter on
%RH
time time
Humidity Chamber
limit sensor
heater
temperature sensor
humidity transmitter
Sample Application
A Series 988 controls the humidity in an environmental chamber. The relative humidity (RH) sensor provides a 4-20mA signal over a 0-100% RH range. The sensor is very sensitive to changes caused by air flow in the chamber. The turbulence in the chamber has the 988 display jumping two to three percent. To remove this display dithering the filter time constant
for input 1 is set to 2 seconds. This will smooth the display and
provide a more realistic reading.
3.8
Optimizing Your Process System with the WATLOW Series 988
General Software Features
TL

Input Linearization

Overview:
In many flow applications the output signal from a flow transmitter represents a squared value of the actual flow. The square root must be extracted from the signal to make it useful to the operator. Many flow transmitters offer this feature in the transmitter itself, but this can add significantly to the cost. Using the square root extraction option in the Series 988 controller can save the operator money. The feature is enabled simply by setting input 1 linearization to square root extraction .
input 1
or input 2 linearization
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
Flow in gallons
transmitter
per minute
flow
Requirements:
The square root extraction feature is standard on any Series 988 controller with universal signal conditioner inputs. The linearization prompt will appear if a process input is se­lected via the universal signal conditioner DIP switches.
16
14
12
10
8
6
4
2
0
J
4 6 8 101214161820
J
J
linearized signal
J
J
J
J
J
J
J
non-linearized signal
J
J
J
4-20mA input signal
Water Treatment Pond
J
J
J
J
Sample Application:
A waste water process engineer needs to control the flow of a solution to be mixed with waste water for treatment of the water. The transmitter provides a 4-20mA output without square root extraction. The engineer used the Series 988 with a universal signal conditioner input and a 4-20mA process output to control the flow. The input signal was linearized using the square root extrac­tion feature of the 988.
The above system has a flow range of 0 to 16 gallons per minute. The range low and range high parameters for input 1 would be set to 0 and 16 respec­tively. The input 1 linearization prompt extraction extraction to linearize the signal it would not be useful for controlling the
. You can see from the above graph that without square root
would then be set to square root
process.
3.9Optimizing Your Process System with the WATLOW Series 988
General Software Features

Ramp To Set Point

Overview
Ramp to set point enables the 988 to ramp the set point at a user defined rate. This allows the 988 to start up a system or change between set points at a rate that will not stress the product or system components. The ramp rate is defined in degrees per minute. Ramp to set point can be initiated at start up only, or at start up and also on any set point changes.
When a ramp is initiated, the starting point for the ramp is the current process value. If the ramp is initiated on start up, the 988 looks at
the process value upon power up, and uses that value as the starting point for the ramp. If a set point change initiates the ramp to set point function, the 988 looks at the process value when the change is made and uses that value as the starting point for the ramp. If the set point is changed during a ramp, the process value at the time of the change becomes the starting point for the new ramp.
Requirements
This feature is standard on all units.
From start up to set point without ramping
1200
1000
800
600
°C
400
200
0
0246810121416
hours after startup
W
A
TL
input 1
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
limit
From start up to set point with 1°/min. ramping
1200
1000
800
600
°C
400
200
0
0246810121416
hours after startup
limit sensor
Sample Application
An engineer needs to control the temperature of a muffle furnace. The furnace set point must be ramped up at a defined rate to prevent stressing the muffle and other system components. By enabling the ramp to set point function in the 988, the engineer can control the rate at which the set point will rise. Ramp to set point is enabled in the Global menu using the ramping function prompt on start up only, select start changes, select set point
. To ramp on start up and on any set point
. The ramp rate is in degrees per minute.
. To ramp
heaters
temperature sensor
heaters
For further protection of the system, output 2, 3 or 4 can be configured as a rate alarm, monitoring the rate of increase or decrease in the process variable on input
1. The alarm low
and alarm high prompts (The "2" in these examples refer to output 2.) establish the ramp-down and ramp-up rate set points, respec­tively, in degrees per minute.
3.10
Optimizing Your Process System with the WATLOW Series 988
General Software Features
TL
TL
TL
TL
TL
TL
TL
TL

Remote Set Point

Overview
The remote set point feature allows the 988 to use a thermocouple, RTD or process signal at input 2, to establish the set point. This feature gives the 988 the ability to have its set point value manipulated by an external source. A common application would use one ramping controller with a set-point retransmit output to ramp multiple 988’s using the remote set point. Or you could use an analog output from a PLC to send set point values to a 988.
Requirements
Input 2 must be either a thermocouple or universal signal conditioner, options 1 or 2.
If the application uses a master controller, choose one of the retransmit options — M (0­20, 4-20mA) or N (0-5, 1-5 or 0-10VDC) — for output 3 of the master.
Match input and output impedances.
zone 1
Master
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO
MAN
MODE
SERIES 988
output 3
zone 2 zone 3 zone 4 zone 5 zone 6 zone 7 zone 8
Remote
W A TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO
MAN
MODE
SERIES 988
Remote
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO
MAN
MODE
SERIES 988
Remote
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO
MAN
MODE
SERIES 988
Remote
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO
MAN
MODE
SERIES 988
Remote
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO MAN
MODE
SERIES 988
input 2 input 2 input 2 input 2 input 2 input 2
Sample Application
An engineer has a machine with eight independent zones of heat. He wants to to change set points on all zones without having to adjust each control indi­vidually. This can be achieved using a 988 with a 0-5VDC retransmit output as the master controller. The seven remote 988’s will use the 0-5VDC signal on input 2 as a remote set point. When the set point is changed on the master controller, the retransmit output changes the set points of the seven remote controllers. By enabling the ramp to set point feature in the master 988, all eight zones are ramped up to set point at a user-defined rate on power up.
The retransmit output from the master 988 is set so that 0VDC represents 0°F and 5VDC represents 800°F. On the remote controllers, set the input 2 DIP switch to the position for the 0-5, 1-5, 0-10VDC process input. In the Input menu, under the input 2 prompt prompt low 2
should be set to ON and decimal 2 set to 0. The range
and the range high 2 parameters will establish the scaling for
, select 0-5. The remote set point
the remote set point input. Range low 2 should be set to 0 and range high 2 should be set to 800. To operate a specific zone ten degrees hotter than the others, increase the range low 2
to 10 and the range high 2 to 810.
Remote
W
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO
MAN
MODE
SERIES 988
Remote
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
input 2
W
DISPLAY
AUTO
MAN
MODE
With remote set point remote prompt
in the System menu, the set point is adjusted using the
enabled and local selected under the local-
increment (up-arrow) and decrement (down-arrow) keys. Selecting remote under the local-remote prompt , disables the increment and decrement keys, allowing the set point value to be manipulated via the input 2 signal.
3.11Optimizing Your Process System with the WATLOW Series 988
General Software Features
Overview:
The retransmit output can be used to transmit an analog signal representing the value of either input process variable or the target set point variable. The retransmit signal is factory configured as either a milliamp or a voltage signal. In choosing the type of retransmit signal the operator must take into account the input impedance of the device to be retransmitted to and the required signal type, either voltage or milliamps.

Retransmit

chart recorder or to generate a set point for other controls in a multi-zone application (see page 3.11).
Requirements:
Output 3 is used for the retransmit option. Choose output type M (0-20, 4-20mA) or N (0­5, 1-5 or 0-10VDC), depending on the signal type. Select the output range in the Output menu.
Typically applications might use the retransmit option to record one of the variables with a
W
A
TL
input 1
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
output 3
limit
Chart Recorder
Enhanced software is not required for this feature.
Heat-treat Oven
limit sensor
heaters
Sample Applications:
The 988 is being used to control the temperature of a heat-treat oven. The temperature of the process must be recorded on a chart recorder. The oven temperature range stays between 600 to 900 degrees F. The chart recorder requires a 4-20mA signal.
temperature sensor
In the Output menu
set analog output to to tag the input 1 process value as the parameter to be retransmitted. Set retransmit low limit retransmit high limit signal to 900. Set retransmit calibrate offset
to 600 to set the low range for the retransmit signal to 600. Set
to 900 to set the high range for the retransmit
to 0, assuming there is
no calibration offset required.
The retransmit output will be 4mA until the oven temperature is greater than 600 degrees F, at which point the signal will increase with tempera­ture to 20mA at 900 degrees F and will not exceed 20mA.
3.12
Optimizing Your Process System with the WATLOW Series 988
General Software Features
TL

Slidewire Feedback

Overview
The 988 can control the position of a valve with a slidewire feedback position indicator. The 988 senses the resistance of the slidewire and compares it to the range low and range high settings to determine the valve position. The controller compares this to the percent output and takes action to match the two by opening or closing the valve.
Set the hunt hunting. The value is set for the percent of output (0.0 to 100.0). When the valve is within
input 1 output 1 (close)
input 2
parameter to limit valve
W
A
TL
W
PROCESS
output 2 (open)
L1 L2 L3 L4
DEV
DISPLAY
% OUT
AUTO
SERIES 988
MAN
MODE
gas flow
Valve Actuator
gas valve
this dead band, a change in output greater than half the hunt parameter is required to trigger action. Output 1 responds to “close” commands and output 2 responds to “open” commands.
Requirements
A slidewire configuration uses at least two inputs and two control outputs. Input 2 must be a slidewire input. Outputs must be compat­ible with the slidewire valve actuators.
Gas-fired Furnace
limit
limit sensor
cut-off valve
temperature sensor
slidewire input
Sample Application
The 988 controls the gas valve for a gas-fired furnace to heat treat large metal parts. First the 988 must be “married” to the slidewire feedback from the valve actuator. To do this, first set the input 2 prompt Advance to the learn low resistance value prompt
to slidewire .
. Close the valve manually to the minimum resistance reading from the slidewire. Select in the upper display and press the MODE key to advance to the learn high resistance value prompt resistance). Select
. Manually open the valve (maximum slidewire
in the upper display and press the MODE key. At this point both the high and low resistance values have been learned and stored in the range low 2
and range high 2 prompts.
You can also manually set the range low and range high values. From the slidewire specifications, determine the low and high resistance values and enter these at the range low
Once the control is operating, adjust the hunt valve oscillations. The hunt parameter sets up a dead band on both sides of the current valve position. The desired valve position is then compared to the
and range high prompts.
parameter, to minimize
actual position. If the difference is greater than the one-half of the hunt value, the 988 repositions the valve to achieve the temperature set point. Once repo­sitioning is complete, the dead band is recalculated for the new valve position.
3.13Optimizing Your Process System with the WATLOW Series 988
Enhanced Software Features
Chapter Four
Enhanced Software Features
Cascade 4.2 Differential 4.4 Dual PID sets 4.5 Duplex 4.6 Ratio 4.7
How to use this chapter:
This chapter describes the software features that are available in the 988 family of Watlow controllers equipped with the enhanced software option.
4.1Optimizing Your Process System with the WATLOW Series 988
Enhanced Software Features

Cascade

Overview
Cascade control can handle a difficult process with minimal overshoot, while reaching the set point quickly. This minimizes damage to system components and allows for oversizing heaters for optimal heat-up rates.
Systems with long lag times between the energy source (heater, steam, etc.) and the measured process value cannot be controlled accurately or efficiently with a single control loop, because a lot of energy can build up before a response is detected. This can cause the system to overshoot the set point, which could damage the heater, product or heat transfer medium, such as a heat transfer fluid.
This graph illustrates a system with a long lag time. Curve A represents a single-control
A
set point
B
C
Two controllers in one
input 1 input 2
The cascade feature allows the Series 988 to internalize the func­tions of two controllers
In1
SP
Outer-loop Controller
%
int
Inner-loop Controller
In2
SP
int
output 1
%
out
generates the internal set point. The Series 988 effectively combines both controllers into a single package.
The primary controller measures the process in the outer, or primary, loop with input 1 and compares the value to the desired set point. The difference between the set point and the process temperature generates an internal percent output value for the second controller. This value cannot be seen by the operator. This internal percent (%
) output generates the
int
internal set point for the secondary, or inner loop. The secondary loop uses this set point and the value of input 2 (typically attached to the heater sheath) to control the heater tem­perature.
time
system with PID parameters that allow a maximum heat-up rate. Too much energy is introduced and the set point is overshot. In most long-lag-time systems the process value may never settle out to an acceptable error. Curve C represents a single-control system tuned to minimize overshoot. This results in unacceptable heat-up rates, with the final value taking hours to reach. Curve B shows a cascade system that limits the energy intro­duced into the system, allowing an optimal heat-up rate with minimal overshoot.
This drawing shows two controllers configured as a cascade system. The second controller
4.2
Optimizing Your Process System with the WATLOW Series 988
Algorithm
The following formulas show how the primary control sends a set point (based on input 2 range-high and range-low values) to the sec­ondary control. The secondary control uses this set point (SP (%
) to the heater.
out
1.) %
2.) SP
3.) %
) to generate a percent output
int
= PID Set A[In1 - SP]
int
= (rH2 - rL2) * %
int
= PID Set B[In2 - SP
out
+ rL2
int
]
int
The critical parameters are the range settings for input 2 of the second controller. The range­high value (rH2) is the maximum allowed set point for the secondary loop. The range-low value (rL2) is the minimum allowed set point.
Enhanced Software Features
TL
In a system controlling a heater this would be the maximum and minimum desired sheath temperatures of the heater. Typically the range­low term is set below the ambient temperature. Otherwise the system could never fully cool down.
Setup
The PID parameters for the two PID sets, PID A and PID B, are determined with the auto-tune function. First the PID B settings (inner loop) are determined by setting the auto-tune prompt
to PID B , which allows for tight control of the energy source at the set point determined by the primary loop. During the tuning process the internal percent (% value is determined by the auto-tune set point parameter
. The default is 90%. This generates a set point for the heater equal to the range high times the
value. The PID A
settings (outer loop) are then determined by setting the auto-tune prompt
to PID A
. During the tuning process the set point
is determined by multiplying the
value by
the set point (SP) entered via the front panel.
Once the system is stable the heater will operate at a value greater than the final pro­cess value (input 1). If this value is significantly different than the set point at which the sec­ondary loop was tuned, adjust the
param­eter so that the tuning set point is near the value at which the heater is controlling.
Requirements
)
int
Cascade control requires enhanced software. Two analog inputs are required to monitor the inner and outer loops. At least one control output is required to control the process.
outer-loop thermocouple
W
A
TL
input 1 input 2
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
limit
limit sensor
Sample Application
A Series 988 is used to heat lube oil to 125°F with a screw-plug-style heater. To protect the oil from breaking down and maximize its life, it is desirable to limit the maximum heater sheath temperature to 250° F.
The 988 is ordered with two thermocouple inputs. Input 2, the inner loop in the cascade configuration, measures the heater sheath. Input 1, the outer loop, measures the lube oil temperature before it leaves the tank. The external set point is 125°. By setting range high 2 set point for the heater sheath will be limited, thus extending the lube oil
to 250° the
life.
heater
Lube Oil Tank
oil outoil in
inner-loop thermocouple
4.3Optimizing Your Process System with the WATLOW Series 988
Enhanced Software Features
TL
Overview
Differential control allows the Series 988 to control one process at a difference to another process. Input 2 acts as a remote set point input. However the displayed set point indi­cates the desired difference between input 1 and input 2. The set point to which input 1 will control to is determined by the equation:

Differential

point, which can be adjusted with the incre­ment (up-arrow) and decrement (down-arrow) keys.
Please note that while in the differential control mode the set point for input 1 cannot be viewed and must be calculated with the equation.
internal set point = input 2 + differential set point
Requirements
Two inputs and the enhanced software option
The lower display shows the differential set
W
A
TL
outside temperature sensor
input 1
input 2
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
are required.
Water Boiler
limit
limit sensor
heating element
Sample Application
The most common application using differential control is to maintain water temperature in a boiler at a differential to the outside air temperature. A thermocouple at input 2 senses the outside air temperature and adjusts the internal set point to maintain the boiler water temperature 120 degree higher. Substituting values we have: boiler temperature = outside temperature + 120
temperature sensor
°
.
In this application the system uses two, type J thermocouples: one to sense boiler water temperature (input 1) and one to sense the outside air tempera­ture (input 2).
To configure the controller, first enable input 2 (set differential control algorithm set the control prompt to differential indicating no differential between input 1 and input 2. Adjust the set point to
. Press the DISPLAY key. The lower display will read 0,
to J). To enable the
in the Global menu
120. The internal set point for input 1 is now equal to the input 2 value plus 120, which will maintain the boiler water temperature 120 degrees higher than the outside air temperature.
4.4
Optimizing Your Process System with the WATLOW Series 988
Enhanced Software Features
TLTL
W
W
A
PROCESS
L1 L2 L3 L4
DEV
% OUT
DISPLAY
MODE
AUTO
MAN
SERIES 988

Dual PID sets

Overview:
Standard software units have a single set of PID parameters. Units with enhanced software can use two independent sets of heat/cool PID parameters, PID A enable dual PID, enter the Global menu and set the algorithm prompt This second set of PID parameters enables the controller to switch between two sets of PIDs, to compensate for changes in the system characteristics. This need can arise from a variety of circumstances, such as significant set point changes (controlling at 250, then controlling at 750), operating a furnace with half a load versus a full load of steel, changing the speed of a conveyor through a curing oven or using different materials in an extruder.
The 988 family can be configured to switch between PID A and PID B based on a process value, a set point value or the event input
input 1
input 2
and PID B . To
to dual PID .
output 1
output 2
limit
status. Use the dual PID
prompt in the Global menu, to select what will cause the switch: process
; set point ; or none
. If process is selected at the prompt, the PID’s will switch based on the crossover process value. If set point selected at
, the PIDs will switch at the
is
crossover set point value, PID A used below the crossover point and PID B above. PID crossover can also be selected via event input by selecting
at the or prompt. PID A is used when the event input switch is open, PID B when closed. (Note : One event input is stan­dard on all units, a second event input is an option)
Requirements:
The 988 family controller needs the enhanced software option to use dual PID sets.
Test Chamber
chiller
limit sensor
heater
temperature sensor
pressure switch
Sample Application:
A test engineer needs to control the temperature in a test chamber that can be operated at normal atmosphere or under vacuum conditions. If he tunes the controller for normal atmospheric conditions, when he reaches the portion of his test that requires a vacuum, he must stop the test and enter new PID parameters to maintain stable temperatures. The system characteristics are so very different, that one set of PID’s will not give satisfactory results under both normal and vacuum conditions.
The 988 solves this problem with the dual PID option. Auto-tuning PID A un­der normal atmospheric conditions, then auto-tuning PID B under vacuum conditions, establishes PID values for two sets of system characteristics. A pressure switch connected to the event input tells the controller when to switch between PID A and PID B, eliminating the need to change PID values manually.
4.5Optimizing Your Process System with the WATLOW Series 988
Enhanced Software Features
Overview
Certain systems require that a single process output control both heating and cooling out­puts. A Series 988 controller configured with enhanced software and a process output can function as two separate outputs. With a 4 to 20mA output the heating output will operate from 12 to 20mA (0 to +100 percent) and the cooling output will operate from 12 to 4mA (0 to -100 percent). In some cases this type of output is required by the device that the 988

Duplex

controls, such as a three-way valve that opens one way with a 12 to 20mA signal and opens the other way with a 4 to 12mA signal. This feature reduces the overall system cost by using a single output to act as two outputs.
Requirements
The duplex control feature requires the en­hanced software and a process output. Duplex applications require a special valve.
Fluid Sample Container
W
A
TL
input 1 output 1
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
hot water
cold water
Sample Application
The system outlined below uses a three-way valve for heating and cooling a fluid sample. Coils surround the container holding the fluid. When the tem­perature needs to be raised, the signal to the valve will be between 12 and 20mA, sending hot water through the coils. When cooling is required, the signal will be between 12 and 4mA, sending cold water through the coils.
temperature transmitter
4.6
Optimizing Your Process System with the WATLOW Series 988
Enhanced Software Features
TL
Overview
This feature allows the 988 to control one process as a ratio of another process. This is especially useful in applications that mix two materials, whether steam, paint or food ingredi­ents.
Input 2 of the 988 measures the part of the process that is either uncontrolled or controlled by another device. The part of the process controlled by the 988 will be maintained at a
W
A
TL
input 1
input 2
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO MAN
MODE
output 1
controlled flow of pigment
flow
transmitter
motorized valve

Ratio

level equal to the quantity measured at input 2 multiplied by the ratio term set by the user. Input 1 monitors the controlled part of the process.
Requirements
Ratio control requires enhanced software. Two analog inputs are required to monitor the process, and at least one output adjusts the controlled part of the process.
Mixing Tank
mixed paint
flow
transmitter
uncontrolled flow of unmixed paint
Sample Application
Blue pigment must be added to paint at a ratio of one part per 100 to create a mixed paint of the desired color. The uncolored paint flows into the mixer in an uncontrolled stream that is set manually and sensed by input 2. A motorized valve controls the flow of pigment, which is moni­tored by the flow sensor to input 1. The flow rate of the uncolored paint determines the set point for the motorized valve that controls the pigment flow. If an operator needs to change the rate of flow for the uncolored paint, the set point will shift accordingly to maintain the correct ratio in the mixing tank.
The application engineer set up this feature in software by choosing ratio
as the control parameter in the Global menu. The set point value displayed was then a ratio value. He entered 0.01 to maintain an input 1:input 2 ratio of 1:100.
4.7Optimizing Your Process System with the WATLOW Series 988
Standard Features
Chapter Five
Standard Features
Alarms 5.2 Auto/Manual 5.4 Diagnostics 5.5 Input errors 5.6 Lockout 5.7 Transmitter power supply 5.8
How to use this chapter:
This chapter describes features that, with the exception of transmitter power supply, are included in every controller in Watlow's Series 988 family.
5.1Optimizing Your Process System with the WATLOW Series 988
Standard Features
Overview
Outputs 2, 3 and 4 can be configured as alarms. To configure an alarm the operator makes several decisions. First we’ll show the difference between a form A, B and C relay.
COM (common)

Alarms

alarm is a deviation, process or rate alarm. Selecting process 1
or deviation 1 references the input 1 value against the alarm 2 low Selecting process 2
and alarm 2 high settings.
or deviation 2 references the input 2 value against the alarm 2 low
and alarm 2 high settings. Input
2 hardware must be connected and enabled.
NC
COM
NO
Form A Relay
Form B Relay
NO (normally open)
NC (normally closed)
COM
Form C Relay
The relays are shown in the “shelf state,” with no power applied. Note that the form C option allows the operator to configure it as either a form A or a form B output. For the purposes of this discussion we will use the form C version, available in outputs 2 and 4 (Output 3 is selected, via a hardware jumper, as either a form A output or a form B output).
You need to make five decisions to configure an alarm output. In the following explanations only output 2 will be configured:
1-Output Type First, choose the type of alarm: either normally energized
or normally de-energized . This means that when there is no alarm condi­tion, the alarm output is energized if normally energized normally de-energized
is selected and de-energized if
is selected.
Selecting rate
references the rate of change of the input 1 value in degrees per minute.
defines a negative rate and
defines a positive rate of change limit.
A process alarm sets an absolute process value independent of the set point. When the process exceeds that value an alarm occurs. The pro­cess value is independent of the set point.
A deviation alarm alerts the operator when the process strays too far from the set point. The operator can enter both high and low alarm settings referenced to the set point. A change in set point causes a corresponding shift in the deviation alarm. Low alarms are set at a nega­tive deviation, and high alarms are set at a positive deviation.
3-Hysteresis This selects the switching hysteresis for the alarm. Once an alarm has occurred it will not clear until the process value is above the alarm­low setting or below the alarm-high settings by a margin equal to the hysteresis.
Example: An alarm starts when the process value reaches the alarm high setting. The alarm will not clear until it is below the high setting by an amount equal to or greater than the alarm hysteresis.
Example: With normally energized
se­lected for output 2 the output will be energized in the non-alarm state. Therefore the normally closed (NC) contact will be open.
2-Alarm Type This prompt allows you to select which input variable will trigger the alarm and whether the
5.2
Optimizing Your Process System with the WATLOW Series 988
4-Latching Alarms can be latching or non-latching. When the alarm condition is removed, a non-latching alarm automatically clears the alarm output and alarm message, if one is present. You must manually clear a latched alarm by pressing the AUTO/MAN key once.
Standard Features
TL
TL
5-Silencing Alarm silencing overrides the alarm at power up, and it allows the operator to silence an alarm with the system still in an alarm condi­tion. The silencing is active until the process has entered the safe region located between the
W
A
TL
input 1 output 1
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 2
Alarm
form C relay
low and high alarm settings. Any future devia­tion outside the safe region triggers an alarm. If the alarm occurs at this point, the output can be silenced by pressing the AUTO/MAN key once, but the alarm message is still displayed.
Oven
limit
limit sensor
heaters
temperature sensor
The temperature is within the normal range. Output 2 is inactive.
W
A
TL
input 1
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
output 2
limit
Alarm
form C relay
An over-temperature condition activates output 2, which turns the alarm on.
Sample Application
An operator is using a deviation alarm to keep a process within +/- 5°F of the set point. Output 2 is set up as a deviation alarm that activates a buzzer. However, when the process powers up in the morning, the process temperature is below the low deviation alarm set point, causing the buzzer to sound until the process reaches the low alarm set point. Selecting ON
at the silencing prompt in the Output menu, disables the alarm output controlling the buzzer until the process gets within the deviation alarm set points. It also allows the operator to silence the buzzer by pressing the AUTO/MAN key once, if an alarm does occur.
limit sensor
heaters
Oven
temperature sensor
5.3Optimizing Your Process System with the WATLOW Series 988
Standard Features
TL

Auto/Manual

Overview:
When it operates automatically the controller uses an input signal (from a thermocouple, RTD, transmitter, etc.) to determine how best to adjust the output power level to match a set point. This constant monitoring of process variables and the corresponding adjustments in the output power level is referred to as closed-loop control. This is the normal mode of operation for most applications.
Manual operation does not use feedback from the input signal to determine a power level. The power level must be adjusted manually by the operator. The controller may or may not be monitoring the process variable. This open-loop control is used for applications in which closed-loop control is not desired, for instance as a diagnostic tool or when the controller detects a sensor break (see Input Errors, page
5.6).
Manual operation provides open-loop control of the outputs from a range of -100 percent to +100 percent power (-100 percent for full cool, +100 percent for full heat). The Series 988
controller allows a negative output value only if one of the control outputs is configured for cool.
If the LED in the corner of the AUTO/MAN key is off, the controller is in the automatic mode and the bottom display is a set point value in degrees or units. If the LED is on, the controller is in the manual mode, and the bottom display indicates the percent power output.
To toggle between auto and manual operation, press the AUTO/MAN key twice. When you press the AUTO/MAN key once, the LED in the lower right hand corner of the AUTO/MAN key, begins to flash. To complete the change, press the AUTO/MAN key again while the LED is flashing. The transition from automatic to manual is a “bumpless transfer,” the control will switch to manual mode maintaining the last power level it used in automatic mode.
Requirements:
Automatic/manual operation is a standard feature on all units.
W
TL
W
A
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
AUTO/MAN Key
Auto/Manual LED
Sample Application:
An engineer has a process that needs to be brought on-line at a low power level, until a predetermined process value is achieved. At this point, the controller can be allowed to take control of the output power level. Utilizing the automatic/manual function, the engineer manipulates the power level in manual mode until it is safe to allow the controller to take control. At that point, he switches the 988 to the automatic mode, letting the controller maintain the output power level.
5.4
Optimizing Your Process System with the WATLOW Series 988
Standard Features

Diagnostics

Overview:
The Series 988 Diagnostics menu allows you to read the software revision, ship date, hardware configuration and ambient temperature without removing power from the control.
To access the Diagnostics menu press the increment (up-arrow) and decrement (down­arrow) keys simultaneously for six seconds. The factory prompt display and panel lockout prompt upper display. Press the increment key until diagnosis Then press the MODE key.
The list below explains the menu prompts:
Date provides the date of the final control test. The first two numbers indicate the week (01 through 52) and the last two show the year.
Soft signifies the control software revision.
The serial number follows “Sn” in the upper
display. The six-digit number begins with the last two digits in the upper display and wraps around to the lower display.
Ambient temperature indicates the tem­perature at the input 1 terminals, in degrees F.
Ambient counts is for factory use only.
Ground counts is for factory use only.
Input 1 counts is for factory use only.
Input 2 counts is for factory use only.
Depending on the modules installed and the DIP switch settings, some of the following input and output type displays will appear:
Types for Inputs 1
no module thermocouple only current detect slidewire universal OFF universal RTD universal tc high gain universal tc low gain universal millivolts universal process event input 2
Types for Outputs 1
no module
0.5A SSR
appears in the upper display.
appears in the lower
in the
and 2
through 4
0.5A SSR w/ suppression
2.0A SSR switched DC form C relay form C relay w/ suppression form A/B Relay process voltage retransmit current retransmit power supply RS-232 communications EIA-485/422 communications
Display tests each display and LED. If any
display or LED is absent contact the factory.
The test output prompt can be used to activate the available outputs on the unit, with the exception of process outputs, transmitter power supply or communications output. To select an output, use the increment or decre­ment key to advance from OFF desired output (output 1 active output 4 active corresponding load LED will light and the output will be energized. This output will remain energized until you select another output or off, or exit the Diagnostic menu.
The open loop prompt enables the open­loop error function. The error message open loop
full on and no temperature change has oc­curred over a period of time, based on system characteristics. This prompt only functions in the proportional control mode.
Requirements:
The Diagnostics menu is a standard feature on all Series 988 controllers. When asking the factory for technical assistance, have the information from the above prompts on hand. All prompts in this menu are read only.
Sample Application:
An engineer needed to figure out why an oven was malfunctioning. She used test output to force ON output 1 , which controlled the heaters. A quick check with a meter revealed a burned out heater element.
flashes in the lower display when ON
is selected and a heat or cool output is
). After three seconds the
to the
through
5.5Optimizing Your Process System with the WATLOW Series 988
Standard Features
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 control­ler 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 the 988 output power level will be when an input error occurs. The bumpless transfer selection allows the 988 to switch from auto­matic 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
determines what

Input Errors

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 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 ( * 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 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.
with the increment (up-arrow) and
or ), the controller:
occurs,
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 con­trollers. 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.
5.6
Optimizing Your Process System with the WATLOW Series 988
Standard Features
Overview:
An array of hardware and software lockout features gives you tremendous flexibility in configuring various levels of user access. The Factory locked out by setting a DIP switch behind the panel. Four levels of lockout can be set from the front panel. A simple switch or a keylock switch can be connected to a digital event input to lock or unlock access to the front panel.
The 988 leaves the factory with DIP switch 2 in the off position, allowing access to the Setup and Factory menus.
and Setup menus can be

Lockout

levels can be selected. Full lockout does not allow the selected menu to be viewed or altered. Read only viewed but not altered. No lockout the selected menu to be viewed and changed.
The lock prompt select several levels of front-panel lockout:
increment+decrement combination
allows a menu to be
allows
allows the operator to
= 0 enables all keys = 1 disables the MODE key = 2 disables MODE and AUTO/MAN keys = 3 disables all keys except the
The front panel can be locked out via digital events at input 2 or 3. This lockout function is enabled by selecting lock input prompt (
or ) in the Global
under an event
Requirements:
All 988 Family controllers are equipped with software and hardware lockout features.
menu.
The software lockout functions appear under the Factory prompt, in the Panel Lockout menu. For each menu, one of three lockout
You can lock out the front panel with the digital event input.
Sample Application:
During the initial configuration and start-up an engineer will need access to all the parameters. Once the process is configured, he will give the operator access to only the process and alarm set points. Security is also an issue, and he wants only authorized operators to have access to these parameters.
1
O N
2
You can lockout the Setup and Factory menus with a DIP switch behind the front panel.
Lockout menus let you configure access to menus and settings.
The Panel Lockout
menu gives him access to all parameters during the start-up. Once the process is online, all Panel lockout menus except System are set to full lockout
. The System menu is set to no lockout , giving the operator access to the alarm set points. Process security is achieved with a keylock switch connected to event input 2. Event input 2 menu, is set to lock
. Without a key, nothing is accessible from the front
in the Global
panel. With a key, process and alarm set points are accessible.
5.7Optimizing Your Process System with the WATLOW Series 988
Standard Features
TL
TL
TL

Transmitter Power Supply

Overview
In an electrically noisy environment or when you have to use a long sensor lead, you may need to use a transmitter to convert the sensor signal to a 4-20mA signal. Normally you would have to buy and install a separate power supply for the transmitter or for other signal conditioning devices, but you can order a Series 988 with a 30mA power supply as one of
Control Room
Heater ControllerEvaporator ControllerPump Controller
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
W
DISPLAY
AUTO
MAN
MODE
output 1
output 2
input 1input 1
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MODE
W
MAN
input 1output 1
output 3
A
TL
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
its outputs. The factory sets the power supply voltage to 20VDC, but you can use DIP switches to change it to 5 or 12VDC as well.
Requirements
A transmitter power supply can be ordered for output 2, 3 or 4.
W
output 1
DISPLAY
AUTO
MAN
output 4
MODE
heater
RTD transmitter power
RTD transmitter
evaporator
humidity transmitter pwr
humidity transmitter
pump
process flow transmitter power
process flow transmitter
Sample Application
An engineer at a food processing plant needs to control several processes from a central control room, which is more than 100 feet away from some of the machines being controlled. Because of the distance and the noisy electrical environment, thermocouples cannot provide dependable readings.
The engineer has installed several Series 988 controllers with power supplies matched to a variety of transducers. DIP switch settings configure the output voltages for 5, 12 or 20VDC.
5.8
Optimizing Your Process System with the WATLOW Series 988
Specifications
Chapter Six
Specifications
Input Table 6.2 Output Table 6.3 Dimensions 6.4 Displays and Keys Chart 6.5 Setup Requirements 6.6 User's Manual 6.7 Product Specification 6.8 Warranty 6.9
How to use this chapter:
This chapter contains charts and lists describing specifications of the Watlow's 988 family of controllers.
Optimizing Your Process System with the WATLOW Series 988 6.1
Specifications

Input Table

988 FAMILY INPUT TYPES Input 1 Input 2 Input 3
0-none
1-basic signal conditioner
type: J, K, T, N, C, D, Pt 2 high temperature moderate sensor accuracy and stability low and high range low sensor cost
2-universal signal conditioner
process input
0-5VDC, 1-5VDC, 0-10VDC, 0-50mVDC,
0-100mVDC, 0-20mA, 4-20mA non-thermal applications sensor determines accuracy and stability long leads of transducer output low and high range best sensor noise immunity moderate to high sensor cost
resistance temperature detector (RTD)
100-ohm platinum type: 1° JIS or DIN, 0.1° JIS or DIN high sensor accuracy and stability low range, moderate sensor cost
thermocouple
type: J, K, T, N, R, S, B, C, D, Pt 2 high temperature moderate sensor accuracy and stability low and high range low sensor cost
3-slidewire feedback
0- to 1200-ohm range determines valve position sensor determines accuracy and stability moderate sensor cost
4-heater current transformer
50mA transformer secondary maximum reads heater current moderate sensor accuracy and stability additional ranges may be available moderate sensor costs
5-digital event
dry switch or DC volts input standard 0-3VDC (open) to 14-36VDC (closed) input 2 0-3VDC (closed) to 14-36VDC (open) input 3 no to low cost
Optimizing Your Process System with the WATLOW Series 9886.2
option available if shaded
Specifications

Output Table

988-FAMILY OUTPUT TYPES Output 1 Output 2 Output 3 Output 4
none
A
solid-state relay
good life/low cost
B- 0.5A, w RC suppression K- 0.5A, w/o RC suppression
open collector
best life/low cost
C- switched DC
electromechanical relay
shortest life/high cost (w maintenance)
D- form C, 5A, w RC suppression E- form C, 5A, w/o RC suppression
electromechanical relay
shortest life/high cost (w maintenance)
J- form A or B, 5A, w/o RC suppression
universal process types
best life/low cost F- 0-5VDC, 1-5VDC, 0-10VDC,
0-20mA, 4-20mA
transmitter power supply
T- 5, 12, 20VDC @ 30mA
process retransmit
chart recorder or data-logging device
M- 0-20mA, 4-20mA N- 0-5VDC, 1-5VDC, 0-10VDC
communications
with a computer
R- RS-232 S- EIA-485, RS-422
option available if shaded
Optimizing Your Process System with the WATLOW Series 988 6.3
Specifications
TL

Dimensions

A
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
2.18"
(55 mm)
W
TL
DISPLAY
AUTO
MAN
MODE
4.03"
(102mm)
(102mm)
W
A
TL
W
PROCESS
L1 L2 L3 L4
Panel
4.03"
DSPY
DEV
% OUT
MODE
2.18"
(55 mm)
AUTO
MAN
SERIES 989
Adjustable
Mounting Bracket
Panel Cutout
Maximum Panel
Thickness
0.38" (9.65mm)
3.62" + 0.03 -0.00 (92mm + 0.8)
1.77 + 0.02 -0.00 (45mm + 0.6)
0.68"
(17 mm)
Note: A minimum of 1.66 inches (42.2 mm) spacing between panel cutouts is recommended.
Optimizing Your Process System with the WATLOW Series 9886.4
4.06"
(103 mm)
Specifications

Displays and Keys Chart

Upper Display
Reads actual process value or operating paramenter value or error code — red or green.
DEV (Deviation) LED
Indicates that the lower display now reads a deviation-from-the-set­point value.
% OUT (percent output) LED
Indicates that the lower display now reads the percent-output value.
Increment (up-arrow) Key
Increases the value or changes the selection in the upper display.
Decrement (down-arrow) Key
Decreases the value or changes the selection in the upper display.
TL
W
A
PROCESS
L1 L2 L3 L4
DEV
% OUT
DISPLAY
AUTO
MAN
MODE
W
Lower Display
Reads Display Loop information, menu or prompt names, or alarm codes — red or green hardware.
L1, L2, L3, L4 LEDs
Shows the active output(s).
DISPLAY Key
Takes the control "home" to the Display Loop (current process values and set point informa­tion) from any menu location.
AUTO/MAN Key
Clears or silences alarms with one press, or toggles between Auto and Manual control with two presses.
AUTO/MAN LED
Indicates Manual control; or, when blinking, indicates that another press will toggle control state.
Incr. + Decr. Combination
Press for three seconds to reach the Setup menu; press for three more seconds to reach the Calibration menu.
Optimizing Your Process System with the WATLOW Series 988 6.5
SERIES 988
MODE + Incr. Combination
Press to move backwards through prompts in a menu. Press and hold the MODE key and use the increment key to move backwards until you reach the top of the menu.
MODE Key
Steps through the menus. In Auto control, enters data selected less than five seconds previ­ously.
Specifications

Setup Requirements

Controllers from the Series 988 family require six steps to set up — from system design to system operation.
1 — Build the Part Number
This booklet helps with the first step, selecting the features your application will need. The features are recorded in a part number, which Watlow uses to custom build each controller.
2 — Set the DIP Switches
The Series 988/989 User’s Manual explains how to set the DIP switches inside the controller chassis. You can set DIP switches to lock out the Factory and Setup menus. Other DIP switches allow you to select some of the input, output and power needs of your application.
3 — Mount and Wire the Controller
The Series 988/989 User’s Manual clearly ex- plains and illustrates the process of correctly mounting and wiring your controller.
4 — Configure the Controller for Your Application
The next step involves determining settings and values, then entering them from the front panel of the 988. Chapter Seven of this book will help you chose the software and parameters to best control your application. The Series 988/989 User’s Manual will guide you through the menus and prompts you will use to configure the controller’s software.
5 — Startup and System Operation
For the final setup step carefully review the previous steps, then turn on the system. Some parameters, such as slidewire feedback, can be auto-tuned after startup. Then system perfor­mance and alarms should be thoroughly tested.
6 — Documentation
Once the system is operating corrcctly, make photocopies of the menu flow diagrams in the user's manual and document all your settings.
Optimizing Your Process System with the WATLOW Series 9886.6
Specifications

User's Manual

The Series 988/989 User’s Manual provides the information you will need to install, wire, config­ure and operate the Series 988 controller, in most applications. Detailed drawings illustrate DIP switch settings, panel mounting and proper wiring of the 988. Easy to use charts and instruc­tions explain how to use the menus and prompts to configure the 988 to your application.
A communications manual and a calibration manual are also available for the Series 988.
Optimizing Your Process System with the WATLOW Series 988 6.7
Specifications

Product Specifications

Control Mode
•Dual input, quad output, optional retransmit of set point or process variable.
•Programmable direct and reverse acting control outputs.
•One step auto-tuning.
Operator Interface
•Local/Remote set point capability.
•Dual, 4-digit LED displays. Upper: 0.4” (10mm), Lower: 0.3” (8mm).
•Mode, Auto/Man, Display, Up and Down keys.
Input
•Contact input for software function select.
•Type J, K, T, N, C(W5), D(W3), E, R, S, B, Pt 2 thermocouple, 100 platinum 1° or 0.1° RTD, or 0-50mV, 0-100mV, 0-20mA, 4-20mA, 0-5VDC, 1­5VDC, 0-10VDC, slidewire, digital event input or heater current options.
•Sensor break protection de-energizes control out­put to protect system or selectable bumpless transfer to manual operation. Latching or non­latching.
°F or °C display or process units, user selectable.
Sensor Ranges
J t/c: 32 to 1500°F or 0 to 816°C K t/c: -328 to 2500°F or -200 to 1371°C T t/c: -328 to 750°F or -200 to 399°C N t/c: 32 to 2372°F or 0 to 1300°C R t/c: 32 to 3200°F or 0 to 1760°C S t/c: 32 to 3200°F or 0 to 1760°C B t/c: 1598 to 3300°F or 870 to 1816°C E t/c: -328 to 1470°F or -200 to 799°C C t/c: 32 to 4200°F or 0 to 2316°C D t/c: 32 to 4200°F or 0 to 2316°C Pt 2: 32 to 2543°F or 0 to 1395°C 1°RTD (JIS):-328 to 1166°F or -200 to 630°C 1°RTD (DIN):-328 to 1472°F or -200 to 800°C
0.1°RTD (JIS and DIN):-99.9 to 999.9°F or -73.3 to 537.7°C 0-5VDC: -999 to 9999 1-5VDC: -999 to 9999 0-10VDC: -999 to 9999 0-20mA: -999 to 9999 4-20mA: -999 to 9999 0-50mVDC: -999 to 9999 0-100mVDC:-999 to 9999 Slidewire: 100 to 1200 Current: 0 to 50mA Potentiometer: 0 to 1200
Output Options
•Solid state relay, 0.5A @ 24VAC min., 253VAC max., opto-isolated, zero cross switching. With or without contact suppression.
•Open collector, switched DC signal provides a minimum turn ON voltage of 3VDC into a mini­mum 500 load; maximum ON voltage not greater than 32VDC into an infinite load.
•Electromechanical relay*, Form C, 5A @ 120/ 240VAC, 6A @ 28VDC, 1/8 hp. @ 120VAC, 125VA @ 120VAC. With or without contact suppression.
•Process, 0-20mA, 4-20mA, 0-5VDC, 1-5VDC, or 0­10VDC.
•Electromechanical relay*, Form A/B, 5A @ 120/ 240VAC, 6A @ 28VDC, 1/8 hp. @ 120VAC, 125VA @ 120VAC. Without contact suppression.
•External transmitter power supply, 5V ±5% @ 30mA, 12V ±5% @ 30mA, or 20V ±5% @ 30mA.
•RS-232 communications or EIA-485/RS-422 com­munications, opto-isolated.
Accuracy
•Calibration accuracy & sensor conformity: ± 0.1% of span, ±1 LSD, 77°F ± 5°F (25°C ± 3°C) ambient & rated line voltage ±10%.
•Accuracy span: 1000°F/540°C minimum.
•Temperature stability: ± 0.2°F/°F (0.1°C/°C) change in ambient.
•Voltage stability: (± 0.01% of span) / (% of rated line voltage).
Agency Approvals
•UL873 and UL508, File #E43684; CSA pending; NEMA 4X.
Terminals
•#6 compression universal head screws, accepts 20-14 gauge wire.
Power
•100 - 240VAC +10%/-15%, 50/60Hz, ± 5%.
•16VA maximum.
•Data retention upon power failure via non-volatile memory.
Operating Environment
•32 to 149°F (0 to 65°C), 0 to 90% relative humid­ity, non-condensing.
* Electromechanical relays are not recommended for PID control. They are warranted for only 100,000 contact closures.
Optimizing Your Process System with the WATLOW Series 9886.8
Specifications

Warranty

The Watlow Series 988 family of controllers is warranted to be free of defects in material and workmanship for 36 months after delivery to the first purchaser for use, providing that the units have not been misapplied. Since Watlow has no control over their use, and sometimes misuse, we cannot guarantee against failure. Watlow’s obligations hereunder, at Watlow’s option, are limited to replacement, repair or refund of pur­chase price, and parts which upon examination prove to be defective within the warranty period specified. This warranty does not apply to damage resulting from transportation, alteration, misuse or abuse.
Optimizing Your Process System with the WATLOW Series 988 6.9
How to Choose the Right 988 to Fit Your Application
Chapter Seven
How to Choose the Right 988 to Fit Your Application
Overview 7.2 Input 7.3 Output 7.4 Software 7.5 Standard Features 7.6 Hardware 7.7 Review and Optimize 7.8 Faxable System Description 7.10 Model Number Information 7.11
How to use this chapter:
The Watlow 988 family of controllers can be used in an almost infinite variety of applications, in part be­cause the inputs, outputs and many other attributes can be factory config­ured to match the requirements of many different processes. A control­ler's model number contains this factory configuration information. This chapter will guide you through the process of optimizing your appli­cation with a Series 988 controller and determining the correct model number.
When you finish, you will have a completed diagram showing how your application can be controlled by a Series 988 controller and a model number for the proper controller configuration.
Experts who are familiar with the Series 988 controller may want to go directly to the Faxable System De­scription on page 7.10.
Make one or more copies of the work­sheet on page 7.10 and any other pages you want to write on. Then sit down with scratch paper and a pencil and carefully work through the steps to determine the best configuration for your application. Use the "Helpful References" listed in the left column of each page.
7.1Optimizing Your Process System with the WATLOW Series 988
How to Choose the Right 988 to Fit Your Application
Step 1: Overview
A. Describe the process that the 988 will control.
HELPFUL REFERENCES
Chapter 1, Test Drives, provides diagrams and explana­tions of several different types of applications.
Chapter 2, Basic Control Strate­gies and Terms, explains the basic concepts and vocabulary of control applications.
W
A
TL
input 1
input 2
input 3
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
output 2
output 3
output 4
B. What raw materials go into the process?
C. What product does the process create?
D. List the sensors, switches and controls used in the process.
E. List the heaters, motors, valves and other devices used in the process.
F. List ambient conditions, performance require­ments and safety concerns involving the process.
G. Make a rough sketch of the process including all of the elements listed above. Be sure to label all of the parts.
7.2
Optimizing Your Process System with the WATLOW Series 988
How to Choose the Right 988 to Fit Your Application
Input #1
98_ _ - _ _ _ - _ _ _ _
Input #2
98_ _ - _ _ _ - _ _ _ _
Input #3
digital event standard
WATLOW
988
Key Features:
Software:
98 _ - _ _ _ _ - _ _ _ _
Power & Hardware:
98 _ - _ _ _ _ - _ _ _ _
Display colors:
98 _ _ - _ _ _ _ - _ _
98__ __ - __ __ __ __ - __ __ __ __
Step 2: Input
A. List all the input devices in your process sketch (Refer to your answer to 1D.).
HELPFUL REFERENCES
Use the complete input table in Chapter 6, Specifications.
See the filled in worksheets in Chapter 1, Test Drives.
0-none
1-basic signal conditioner
2-universal signal conditioner
process input
resistance temp. detector
thermocouple
3-slidewire feedback
4-heater current transformer
5-digital event
B. List all of the parameters and specifications that apply to each of the above items.
C. Input types must match the appropriate input of the 988. Use the input chart on page 6.2 to assign each input device to one of the 988’s inputs.
D. Use the information on your list to fill out the input boxes in your photocopy of the worksheet from page 7.10.
Inputs
123
option available if shaded
Fill in input device information and codes from page 6.2.
7.3Optimizing Your Process System with the WATLOW Series 988
How to Choose the Right 988 to Fit Your Application
Output #1
98_ _ - _ _ _ - _ _ _ _
Output #3
98_ _ - _ _ _ _ - _ _ _
Output #2
98_ _ - _ _ _ - _ _ _ _
Output #4
98_ _ - _ _ _ _ - _ _ _
WATLOW
988
Key Features:
Software:
98 _ - _ _ _ _ - _ _ _ _
Power & Hardware:
98 _ - _ _ _ _ - _ _ _ _
Display colors:
98 _ _ - _ _ _ _ - _ _
Step 3: Output
A. List all the output devices in your process sketch (Refer to your answer to 1F.).
HELPFUL REFERENCES
Use the complete output table in Chapter 6, Specifications.
Alarms and, transmitter power supply are explained in Chapter 5, Other Features.
See the filled in worksheets in Chapter 1, Test Drives.
A-none
solid-state relay
B-0.5A w RC suppression
K-0.5A w/o RC suppression
open collector
C-switched DC
electromechanical relay
D-form C, 5A w RC supp
E-form C, 5A w/o RC supp
electromechanical relay
J-form A or B, 5A w/o RC spp
universal process types
F-0-5VDC, 1-5VDC, 0-10VDC;
transmitter power supply
T-5, 12, 20VDC @ 30 mA
process retransmit
M-0-20mA, 4-20mA
N-0-5VDC, 1-5VDC, 0-10VDC
communications
R-RS-232
S-EIA485, RS-422
1234
0-20mA, 4-20mA
options available if shaded
B. List all of the parameters and specifications that apply to each of the above items.
C. Output types must match the appropriate output of the 988. Use the Output Chart on page 6.3 to assign each output device to one of the 988’s out­puts.
D. Use the information on your list to fill in the output boxes in your photocopy of the worksheet from page 7.10.
Outputs
E. Make a sketch of your application on your photo­copy of the worksheet. Make sure the appropriate devices are connected to the appropriate inputs and outputs.
Fill in output devices and codes from page
6.3.
7.4
Optimizing Your Process System with the WATLOW Series 988
How to Choose the Right 988 to Fit Your Application
_
_
_
_
Step 4: Software
A. Determine what software features your process will require.
HELPFUL REFERENCES
General Software Features
auto-tune 3.2 burst fire 3.3 communications 3.4 dead band 3.5 digital event 3.6 heater current 3.7 input filter 3.8 input linearization 3.9 ramp to set point 3.10 remote set point 3.11 retransmit 3.12 slidewire feedback 3.13
Enhanced Software Features
cascade 4.2 differential 4.4 dual PID sets 4.5 duplex 4.6 ratio 4.7
See the filled in worksheets in Chapter 1, Test Drives.
B. Determine the process range or ranges that the software must maintain in the process.
C. Determine what conditioning, if any, is needed for your input data.
D. Will you use any enhanced software features?
E. Use the information you have just gathered to fill in the software box in your photocopy of the worksheet from page 7.10.
Outp
WATLOW
988
Key Features:
Check the software features you will use. If you will use any enhanced software features fill in a "B", otherwise fill in an "A".
_ _
_ _
Software:
98 _ - _ _ _ _ - _ _ _ _
Power & Hardware:
98 _ - _ _ _ _ - _ _ _ _
Display colors:
98
Outp
98
Outp
98
Outp
- __ __ __ __ - __ __ __ __
98 _ _ - _ _ _ _ - _ _
98
7.5Optimizing Your Process System with the WATLOW Series 988
How to Choose the Right 988 to Fit Your Application
Step 5: Standard Features
A. This section lists features that may be important to your application that are built into all of the 988
HELPFUL REFERENCES
calibration 5.3 diagnostics 5.4 factory settings 5.5 errors (input) 5.6 lockout 5.7 moisture resistance 5.8 displays and keys 6.5 setup 6.6 isolation 6.7 training 6.8 manual 6.9 spec chart 6.10 warranty 6.11
family of controllers. None of this information is needed on your worksheet, but you might want to take some time to learn about these features.
calibration diagnostics factory settings errors (input) lockout water- and corrision-resistant front panel display and keys setup isolation user's manual product specifications three-year limited warranty
7.6
Optimizing Your Process System with the WATLOW Series 988
How to Choose the Right 988 to Fit Your Application
_
Power & Hardware:
98 _ - _ _ _ _ - _ _ _ _
Display colors:
98 _ _ - _ _ _ _ - _ _
_ __ __ __ - __ __ __ __
Step 6: Hardware
A. Would the controller fit your applications panel
HELPFUL REFERENCES
lockout 5.7 dimensions 6.4 display & key chart 6.5 specifications 6.8
better in its vertical configuration (986 or 988) or horizontal configuration (987 or 989)? Be sure to check all dimensions for fit.
B. Will you connect your controler to a 100- 240­volt power supply (988 or 989) or a 24-28-volt power supply (986 or 987)? (Either configuration works with either AC or DC power.)
C. Each of the two displays in the 988 family can be either red (R) or green (G). Choose a color for each display.
vertical horizontal
100-240 V 988 989
24-28 V 986 987
D. You can lockout access to controller settings with software, hardware switches or with an digital event input. All of these are standard features.
E. Fill in the appropriate spaces in your photocopy of the worksheet from page 7.10. You should have all the information you need to fill in the part num­ber.
Use the table to choose and fill in your power and hardware configuration.
Choose the upper and lower display colors. RR - red upper, red lower RG - red upper, green lower GG - green upper, green lower GR - green upper, red lower
7.7Optimizing Your Process System with the WATLOW Series 988
How to Choose the Right 988 to Fit Your Application
Step 7: Review and Optimize
A. Review the last six steps looking for errors and opportunities to optimize your application’s use of
HELPFUL REFERENCES
Chapter 1, Test Drives, provides diagrams and explana­tions of several different types of applications.
Chapter 2, Basic Control Strate­gies and Terms, explains the basic concepts and vocabulary of control applications.
the Series 988 controller..
B. If any of the inputs or outputs are not used by your application, check whether they could be used to enhance your application, perhaps with the addi­tion of an alarm or the communications option.
C. How might your needs change in the future? It's more efficient and economical to order options now.
D. Make several copies of the worksheet on the next page and “test drive” your application through dif­ferent conditions. What happens if conditions ex­ceed limits? What happens if a device breaks down?
E. Go over your work with a colleague and/or a Watlow sales rep to check whether you have over­looked anything.
F. If you made any changes on your worksheet, revise your model number.
7.8
Optimizing Your Process System with the WATLOW Series 988
How to Choose the Right 988 to Fit Your Application
Notes Page
7.9Optimizing Your Process System with the WATLOW Series 988
TL
Faxable Series 988 System Description
How to Choose the Right 988 to Fit Your Application
date: # of pages:
to: from:
comp/dept: comp/dept:
phone: phone:
fax: fax:
Output #1
Input #1
98_ _ - _ _ _ - _ _ _ _
Input #2
98_ _ - _ _ _ - _ _ _ _
Input #3
digital event standard
WATLOW
Key Features:
Software:
98 _ - _ _ _ _ - _ _ _ _
Power & Hardware:
98 _ - _ _ _ _ - _ _ _ _
Display colors:
98 _ _ - _ _ _ _ - _ _
988
98_ _ - _ _ _ - _ _ _ _
Output #2
98_ _ - _ _ _ - _ _ _ _
Output #3
98_ _ - _ _ _ _ - _ _ _
Output #4
98__ __ - __ __ __ __ - __ __ __ __
Sketch your application in this space.
W
A
TL
input 1
input 2
input 3
Make photocopies of this page. Do not write on the original. Use the informa­tion you gathered in the previous pages to fill in the boxes and model number.
7.10
W
PROCESS
L1 L2 L3 L4
DEV
% OUT
SERIES 988
DISPLAY
AUTO
MAN
MODE
output 1
output 2
output 3
output 4
Optimizing Your Process System with the WATLOW Series 988
98_ _ - _ _ _ _ - _ _ _
How to Choose the Right 988 to Fit Your Application
Series 988/989 Model Number Information
98 _ _ - _ _ _ _ - _ _ _ _
Hardware
6 = Vertical mounting, 24-28 V 7 = Horizontal mounting, 24-28 V 8 = Vertical mounting, 100-240 V 9 = Horizontal mounting, 100-240 V
Software
A = Standard B = Enhanced (with cascade, ratio, dual PID, differential)
#1 Input
1 = Basic thermocouple signal conditioner
2 = Universal signal conditioner
#2 Input
0 = None 1 = Basic thermocouple signal conditioner
2 = Universal signal conditioner 3 = Slidewire feedback 4 = Current transformer 5 = Second digital event (one digital event is standard on all units)
#1 Output
B = Solid state relay, Form A, 0.5A, with RC suppression C = Switched DC, open collector, isolated D = *Electromechanical relay, Form C, 5A, with RC supression E = *Electromechanical relay, Form C, 5A, without RC suppression F = Universal process, 0-5VDC, 1-5VDC, 0-10VDC, 0-20mA, 4-20mA K = Solid state relay, Form A, 0.5A, without RC suppression
#2 Output
A = None B = Solid state relay, Form A, 0.5A, with RC suppression C = Switched DC, open collector, isolated D = *Electromechanical relay, Form C, 5A, with RC suppression E = *Electromechanical relay, Form C, 5A, without RC suppression F = Universal process, 0-5VDC, 1-5VDC, 0-10VDC, 0-20mA, 4-20mA K = Solid state relay, Form A, 0.5A, without RC suppression T = External signal conditioner power supply, 5, 12 or 20VDC @ 30mA
#3 Output
A = None B = Solid state relay, Form A, 0.5A, with RC suppression C = Switched DC, open collector, isolated J = *Electromechanical relay, Form A or B, 5A, without RC suppression K = Solid state relay, Form A, 0.5A, without RC suppression M = Retransmit, 0-20mA, 4-20mA N = Retransmit, 1-5VDC, 0-10VDC, 0-5VDC T = External signal conditioner power supply, 5, 12 or 20VDC @ 30mA
#4 Output
A = None B = Solid state relay, Form A, 0.5A, with RC suppression C = Switched DC, open collector, isolated D = *Electromechanical relay, Form C, 5A, with RC suppression E = *Electromechanical relay, Form C, 5A, without RC suppression K = Solid state relay, Form A, 0.5A, without RC suppression R = Isolated RS-232 communications S = Isolated EIA-485/RS-422 communications T = External signal conditioner power supply, 5, 12 or 20VDC @ 30mA
Display Color (Upper/Lower)
GG = Green/Green GR = Green/Red RG = Red/Green RR = Red/Red
(excluding Type R, S and B)
(excluding Type R, S and B)
*Electromechanical relays are not recom­mended for PID control. They are warranted for only 100,000 contact closures
Sensor Ranges
J t/c: 32 to 1500° F
K t/c: -328 to 2500°F
T t/c: -328 to 750° F
N t/c: 32 to 2372°F
R t/c: 32 to 3200°F
S t/c: 32 to 3200°F
B t/c: 1598 to 3300°F
E t/c: -328 to 1470°F
C t/c: 32 to 4200°F
D t/c: 32 to 4200°F
Pt 2: 32 to 2543°F
1°RTD (JIS): -328 to 1166°F
1°RTD (DIN): -328 to 1472°F
0.1°RTD (JIS
100 platinum
and DIN): -99.9 to 999.9°F
0-5VDC: -999 to 9999 1-5VDC: -999 to 9999 0-10VDC: -999 to 9999 0-20mA: -999 to 9999 4-20mA: -999 to 9999 0-50mVDC: -999 to 9999 0-100mVDC: -999 to 9999 Slidewire: 100 to 1200 Current: 0 to 50mA Potentiometer: 0 to 1200
0 to 816°C
-200 to 1371°C
-200 to 399°C
0 to 1300°C
0 to 1760°C
0 to 1760°C
870 to 1816°C
-200 to 799°C
0 to 2316°C
0 to 2316°C
0 to 1395°C
-200 to 630°C
-200 to 800°C
-73.3 to 537.7° C
7.11Optimizing Your Process System with the WATLOW Series 988
Index
Index
A
A/D overflow error 5.6 A/D underflow error 5.6 accuracy 6.8 actuator interfaces 2.6 address prompt 3.4 agency approvals 6.8 alarm 2 high 5.2 alarm 2 low 5.2 alarm high 3.10 alarm low 3.10 alarm reset 3.6 alarm silencing 1.5, 1.7 alarms 2.6, 5.2, 6.6 algorithm prompt 4.5 aluminum melting furnace 1.6 ambient counts 5.5 ambient temperature 2.6, 5.5 analog output 3.12 annunciation output 2.6 annunciator 2.8 auto mode 5.6 auto reset 2.4 auto-tune 1.3, 2.3, 3.2, 4.3, 4.5,
6.6 auto-tune prompt 3.2, 4.3 auto-tune set point 3.2 auto-tune set point parameter
4.3 auto-tuning 2.3, 4.5 AUTO/MAN key
3.2, 5.2, 5.3, 5.4, 5.6, 5.7, 6.5 AUTO/MAN LED 6.5 auto/manual 5.4 automatic mode 5.4 automatic reset 2.2, 2.4 automatic tuning 2.3
B
Barber Coleman 560 1.4 basic signal conditioner 6.2 baud rate 2.6, 3.4 boiler 4.4 break protection 2.10 bumpless transfer 5.4, 5.6 burst fire 2.6, 2.8, 3.3, 3.7 buzzer 5.3
C
calibration manual 2.7 Calibration menu 6.5 calibration offset 2.8 cascade 1.6, 1.7, 2.7, 2.8, 4.2 case 2.7 chart recorder 2.6, 3.12 chattering 2.2 closed loop 2.2, 2.8, 5.4 cold junction 2.8, 2.10 communications 2.6, 3.4, 6.3 Communications menu 3.4 compression molding press 3.7 computer 3.4 configuration error 5.6 configure 6.6 control mode 2.2, 6.8 control output action 3.6 control parameter 4.7 control prompt 4.4 control room 5.8 control software revision 5.5 control strategies 2.2 controller environment 2.6 controller operation 2.7 CSA 2.7, 6.8 current 3.7 current monitor 2.6, 5.5 current retransmit 5.5 current transformer 2.8
D
damping 2.4 data bits and parity 3.4 dead band 2.8, 3.5 decimal 2 3.11 decrement key
3.11, 4.4, 5.6, 6.5 default parameters 2.8 defects 6.9 derivative
2.3, 2.4, 2.8, 2.10, 3.2 derivative 1 5.2 derivative 2 5.2 Deutsche Industrial Norms 2.8 DEV (deviation) LED 6.5 deviation alarm 1.5, 2.6, 5.2, 5.3
device address 3.4 diagnostics 5.4, 5.5 Diagnostics menu 2.7, 5.5 differential 2.7, 2.8, 4.4 digital event 3.6, 5.7, 6.2 dimensions 2.6, 6.4 DIN 2.8 DIP switch 3.11, 5.7, 6.6, 6.7 display 5.5 DISPLAY key 3.7, 4.4, 6.5 display loop 6.5 displays 6.5, 7.8 documentation 6.6 down-arrow key, see decrement
key droop 2.2, 2.3, 2.4, 2.8 drying grain 1.4 dual PID 1.3, 4.5 duplex 2.8, 4.6 duty cycle 2.8
E
EIA-485/422 1.9, 2.6, 3.4, 5.5,
6.3
electrically noisy environment
5.8 electromechanical relays 6.3, 6.8 enclosure heater 2.7 enhanced software 3.2, 4.1-
4.7, 7.6 environmental chamber 3.5, 3.8 error 2.7 error code 5.6 event input 2.7, 4.5 event input 1 prompt 3.6 event input 2 5.5, 5.7 external transmitter power supply
2.8 extruder 1.2
F
factory menu 5.7, 6.6 factory prompt 5.5, 5.7 failure mode prompt 5.6 field calibration 2.7 filter 2.8 filter time constant 3.8
Optimizing Your Process System with the WATLOW Series 988
8.1

Index

fixed power output 5.6 flow transmitter 1.8, 3.9 form A relay 2.8, 5.2, 6.3 form A/B relay 5.5 form B relay 2.8, 5.2, 6.3 form C relay 2.9, 5.2, 5.5, 6.3 four dashes 5.6 front panel 2.7 front panel lockout 3.6 full lockout 5.7
G
gas valve 5.6 gas-fired furnace 3.13 gaskets 2.7 Global menu
3.6, 3.10, 4.4, 4.5, 4.7, 5.6, 5.7 ground counts 5.5 ground loops 2.5
H
hardware 7.8 heat-treat oven 3.12 heater current 1.2, 2.7, 3.3, 3.7 heater current transformer 6.2 horizontal version (989) 1.7, 7.8 hose-down 2.7 hunting 1.5, 2.9, 3.13 hysteresis 2.2, 2.9, 5.2
I
idle set point 3.6 idle temperature 3.6 increment key
3.11, 4.4, 5.6, 6.5 incubator 3.6 input 1 counts 5.5 input 1 linearization 3.9 input 2 counts 5.5 input 2 linearization 3.9 input 2 prompt 3.7, 3.11, 3.13 input devices 7.4 input errors 5.6 input filter 3.8 input linearization 2.9, 3.9 Input menu 3.7, 3.11 Input Table 6.2 inputs 2.5, 5.5, 6.8 integral 2.2, 2.4, 2.9, 2.10, 3.2 integration function 2.3
interactive process variables 2.7 interface prompt 3.4 internal percent 4.3 internal set point 4.2, 4.4 isolation 2.9
J
JIS 2.9 Joint Industrial Standards 2.9
K
keylock switch 5.7 keys 6.5
L
latching alarm 2.6, 5.2 learn high resistance value 3.13 learn low resistance value 3.13 LED 5.4, 5.5, 6.5 limits 1.7, 2.5, 2.6 linearization 2.9 local 3.11 local-remote prompt 3.11 lockout 3.6, 5.7 long lag times 4.2 long sensor lead 5.8 loop error detect 3.7 louver 1.4, 1.5 low-level contact 1.9 low-pass filter 3.8 lower display 6.5
M
manual mode 5.4, 5.6 manual tuning 2.3 master-remote 2.6, 3.11 mechanical relays 2.6 MODE key
3.6, 3.13, 5.5, 5.7, 6.5 model number 7.1 motorized valve 4.7 mounting 6.4, 6.6, 6.7 muffle furnace 3.10 multi-zone application 3.12
N
natural oscillation 2.4 NEMA 4X 2.7, 2.9, 6.8 no lockout 5.7
no module 5.5 noise immunity 2.5 non-latching alarm 2.6, 5.2 non-volatile checksum error 5.6 normally de-energized 5.2 normally energized 5.2
O
offset 2.4 ON/OFF control 2.2, 2.9 open collector 3.3, 6.3 open loop 2.2, 2.9, 5.4 open loop prompt 5.5 operating environment 6.8 operator interface 6.8 optimize 7.9 output 1 active 5.5 output 4 active 5.5 output devices 7.5 Output menu 3.12, 5.3 Output Table 6.3 outputs 2.5, 2.9, 5.5, 6.8 outputs, turn off 3.6 overshoot 2.3, 2.4, 2.9
P
P control 2.9 paint 4.7 panel cutouts 6.4 Panel Lockout menu 5.7 panel lockout prompt 5.5 part number 6.6 PD control 2.9 PDR control 2.7, 2.9 percent power output 5.4 percent power output (%OUT)
LED 6.5 personal computer 2.6 PI control 2.9 PID 2.2, 2.3, 2.7, 2.9,
2.10, 3.2, 4.2, 4.3, 4.5 PID A 4.3, 4.5 PID B 4.3, 4.5 PID menus 3.5 PLC 3.11 power 6.8, 7.7 power supply 5.5, 5.8, 7.8 pressure switch 4.5 process 2.2, 4.5, 5.5 process 1 5.2
8.2
Optimizing Your Process System with the WATLOW Series 988
Index
process 2 5.2 process 2 prompt 3.7 process alarms 2.6, 3.7, 5.2 process input 6.2 process retransmit 6.3 process variable 2.9 product specifications 6.8 proportional band 2.4, 2.9, 3.2 proportional control mode 5.5 proportional derivative control
with manual reset 2.9 proportional-integral control 2.3 proportional-integral-derivative
(PID) 2.3 proportioning control
2.2, 2.9, 2.10
proportioning control with deriva-
tive 2.9 protocol 3.4
Q
QCD 3.3 QPAC 3.3 questions and answers 2.5
R
radio frequency interference 1.7 radio frequency noise 3.3 ramp rate 3.10 ramp to set point 1.3, 2.7, 3.10 ramping function prompt 3.10 range 2.5 range high 2 3.11, 3.13, 4.3 range high 2 prompt 3.7 range low 2 3.11, 3.13 range low 2 prompt 3.7 rate 2.3, 2.4, 2.10, 5.2 rate alarm 3.10 rate band 2.9 ratio control 1.8, 1.9,
2.7, 2.9, 4.7 read only 5.7 reference junction 2.10 relative humidity 3.8 remote set point 3.6, 3.11, 4.4 reset 2.4, 2.10 resistance temperature detector
(RTD) 2.5, 2.10, 6.2 retransmit 2.6, 2.10, 3.12 retransmit calibrate offset 3.12
retransmit high limit 3.12 retransmit low limit 3.12 retransmit options 3.11 RFI 3.3 RS-232 3.4, 5.5, 6.3 RS-422 1.9, 2.6, 3.4, 6.3 RTD 2.5, 2.10, 6.2
S
safety limits 2.6 SCR firing card 3.3 security 2.7, 5.7 semiconductor oven 3.3 sensor break 5.4, 6.8 sensor cost 2.5 sensor fails 5.6 sensor over-range error 5.6 sensor ranges 6.8 sensor under-range error 5.6 serial communications 3.4 serial number 5.5 serial port 3.4 Series 988/989 User’s Manual
6.6, 6.7 set point 3.10, 4.5 setup 3.4, 6.6 Setup menu 5.6, 5.7, 6.5, 6.6 ship date 5.5 shipping overseas 2.7 signal transmitter 2.5 silencing alarm 2.6, 5.3 sketch 7.1-7.11 slidewire feedback
1.4, 2.7, 2.10, 3.13, 6.2, 5.5 slidewire valve actuators 3.13 software features 7.6 software revision 5.5 solid-state output 2.6 solid-state relay 3.3, 6.3 spacing between controllers 2.6 specifications 6.8 square root extraction 3.9 SSR firing card 3.3 standard features 5.1-5.8, 7.7 start 3.10 startup 2.7, 6.6 switch PID sets 3.6 switched DC 5.5 switching sensitivity 2.10 system cycle time 2.4
system diagram 2.5 System menu 3.11, 5.7 system response time 2.4 system stress 2.7 system tuning 2.3
T
terminals 6.8 test chamber 3.4, 4.5 test output prompt 5.5 thermal lag 2.3 thermal system 2.10 thermocouple 2.10, 6.2 thermocouple only 5.5 three-mode control 2.10 three-way valve 4.6 time proportioning control 2.2,
2.10
transmitter power supply
2.10, 6.3 tune 3.2 Tuning of Industrial Control
Systems 2.4 tuning reference 2.4 tuning the system 2.4
U
UL 1.9, 2.7, 6.8 UL recognized 1.9 uncontrolled stream 4.7 universal millivolts 5.5 universal off 5.5 universal process types 5.5, 6.3 universal RTD 5.5 universal signal conditioner
3.9, 6.2 universal tc high gain 5.5 universal tc low gain 5.5 up-arrow key, see increment key updates 2.5 upper display 6.5 urethane mixing 1.8 user's manual 6.7
V
vacuum 4.5 valve oscillations 3.13 variable-time-base 2.6, 2.8, 3.3 vertical configuration 7.8
Optimizing Your Process System with the WATLOW Series 988
8.3
Index
voltage retransmit 5.5
W
warranty 6.9 waste water process 3.9 wire length 2.5 wiring 6.6, 6.7
Z
zero-cross fired 1.7, 3.3 zero-cross switching 3.3 zero-switching 2.8, 2.10
Prompst, parameters and
menus
RS-232 5.5 EIA-485/422 5.5
A
alarm 2 high 3.10, 5.2 alarm 2 low 3.10, 5.2 retransmit calibrate offset 3.12 ambient counts 5.5 control action output 3.6 address 3.4 alarm 2 energized 5.2 alarm 2 de-energized 5.2 algorithm 4.5 alarm reset 3.6 ambient temperature 5.5 analog output 3.12 retransmit high limit 3.12 retransmit low limit 3.12 auto-tune set point 3.2, 4.3 auto-tune 3.2, 4.3
B
baud rate 3.4 bumpless transfer 5.6 burst fire 3.3
C
input 1 counts 5.5 input 2 counts 5.5 control 4.4, 4.7 communications 3.4 current 3.7, 5.5
D
data bits and parity 3.4 date 5.5 dead band A 3.5 dead band B 3.5 switched dc 5.5 deviation 1 5.2 deviation 2 5.2 decimal 2 3.11 diagnostics 5.5 differential 4.4
8.4
Optimizing Your Process System with the WATLOW Series 988
Index
display test 5.5
E
error 1-1 5.6 error 1-2 5.6 error 1-3 5.6 error 1-4 5.6 error 2-1 5.6 error 2-2 5.6 error 2-3 5.6 error 2-4 5.6 event input 1 3.6, 4.5, 5.7 event input 2 4.5, 5.5, 5.7 error 5 5.6 error 9 5.6
F
failure 5.6 factory 5.5, 5.7 filter time constant 1 3.8 full 5.7
G
ground counts 5.5
H
learn low resistance 3.13
N
no module 5.5, 5.7
O
open loop 5.5 output 3.12 output 1 type 5.5 output 4 type 5.5 output 1 active 5.5 output 4 active 5.5
P
switch PID sets 3.6, 4.5 PID 2 4.5 PID A 3.2, 4.3, 4.5 PID B 4.3, 4.5 panel lockout 5.5, 5.7 process 1 5.2 process 2 3.7, 5.2 process value 1 3.12 process 4.5, 5.5 protocol 3.4
serial number lower 5.5 error output 5.6 software 5.5 power supply 5.5 solid state 0.5A surppress
5.5
solid state 0.5A 5.5 solid state 2A 5.5 set point 3.10, 4.5 start 3.10
T
thermocouple only 5.5 test output 5.5 tune 3.2
U
universal millivolts 5.5 universal OFF 5.5 universal process 5.5 voltage retransmit 5.5 universal RTD 5.5 universal tc high 5.5 universal tc low 5.5
hunt 3.13 hysteresis 5.2
I
idle set point 3.6 input 2 3.7, 3.11, 3.13 input 3.7 communications interface
3.4
current retransmit 5.5 input 1 type 5.5 input 2 type 5.5
L
local 3.11 local-remote 3.11 latching 2 5.2 linearization 1 3.9 linearization 2 3.9 front panel lockout 3.6, 5.7 loop error detect 3.7 learn high resistance 3.13
R
remote 3.11 ramp rate 3.10 rate 5.2 ratio 4.7 read 5.7 range high 2 3.7, 3.11, 3.13 range low 2 3.7, 3.11, 3.13,
4.3
relay A/B 5.5 relay C surppress 5.5 relay C 5.5 root extraction 3.9 ramping 3.10 remote set point 3.6, 3.11
S
setup 3.4, 4.5, 5.7 silencing 2 5.3 slidewire 3.13, 5.5 serial number upper 5.5
Optimizing Your Process System with the WATLOW Series 988
8.5
Watlow maintains a worldwide network of stocking distributors.
Designer and Manufacturer of
Watlow St. Louis • 12 0 01 Lackland Road • St. Louis, MO 6 3146 USA • Phone: 314 - 8 7 8-4600 • FAX: 314 - 87 8 - 6814
WATLO W
Watlow Products and Technical Support Delivered Worldwide
Your Authorized Watlow Distributor is:
W988-AGV2-9444
North American Sales Offices
Region 1
Boston 508-655-2225
Region 2
New York, Upstate 716-438-0454
Region 3
New York/New Jersey 908-549-0060
Region 4
Philadelphia 215-345-8130
Region 5
Atlanta/Greenville 404-908-9164 Charlotte/Columbia 704-847-4000 Nashville 615-833-2636 Orlando 407-351-0737 Winston Salem 910-945-5957
Region 6
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Region 7
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Region 8
Cleveland 216-838-5522 Pittsburgh 412-322-5004
Region 9
Detroit 810-651-0500
Region 10
Chicago 708-490-3900 Indianapolis 317-575-8932 Milwaukee 414-255-7725
Region 11
St. Louis 314-878-4600
Region 12
Dallas 214-422-4988 Houston 713-440-3074
Region 13
Denver 303-440-9345 Kansas City 913-897-3973 Tulsa 918-496-2826
Region 14
Minneapolis 612-431-5700
Region 15
Portland 206-253-5855 San Francisco 408-980-9355 Seattle 206-546-6817
Region 16
Los Angeles 714-935-2999 Phoenix 602-258-9206 San Diego 619-728-9188
Asian Sales Offices
Korea 82-2-563­5777
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European Sales Offices
France 33-1-3073­2425
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Printed on Recycled Paper, 10% Postconsumer Waste.
Made in the USA
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