AUBER INSTRUMENTS
WWW.AUBERINS.COM
2011.02
P4/8
The things you should know about alarm
1) Absolute alarm and deviation alarm
High (or low) limit absolute alarm is set by the specific temperatures that the
alarm will be on. Deviation high (or low) alarm is set by how many degrees
above (or below) the control target temperature (SV) that the alarm will be on.
e.g. Assuming ALM1=1000 ºF, Hy-1=5 ºF, SV=700 ºF. When the probe
temperature (PV) is above 705, the deviation alarm will be on. When the
temperature is above 1000 ºF, the process high alarm will be on. Later, when
SV changes to 600 ºF, the deviation alarm will be changed to 605 but process
high alarm will remain the same. Here the Hysteresis Band (Hy) setting is
ignored. Please see 4.5.2 for details.
2) Alarm Suppression feature
Sometimes, user may not want the low alarm to be turned on when starting
the controller at a temperature below the low alarm setting. The Alarm
Suppression feature will suppress the alarm from turning on when the
controller is powered up (or SV changes). The alarms can only be activated
after
the PV has reached SV.
This feature is controlled by the B constant of the COOL parameter (see 4.14).
The default setting is alarm suppression on. If you use the AL1 or AL2 relay for
a control application that needs it to be active as soon as the controller is
powered up, you need to turn off the alarm suppression by setting B=0.
3) Assignment of the relays for the alarms
AL1 and AL2 are the name of the two relays used for alarm output. AL1 is the
alarm relay 1 and AL2 is alarm relay 2. Please do not confuse the relays with
alarm parameter ALM1 (process high alarm) and ALM2 (process low alarm).
Either the AL1 or the AL2 can be used for any of the four alarms. AL-P (alarm
output definition) is a parameter that allows you to select the relay(s) to be
activated when the alarm set condition is met.
You can set all four alarms to activate the one relay (AL1 or AL2), but you
can’t activate both relays for with just one alarm.
4) Display of the alarm
When AL1 or AL2 relay is activated, the LED on the upper left will light up. If
you have multiple alarms assigned to a single relay, you might want to know
which alarm activated the relay. This can be done by setting the E constant in
the AL-P parameter (see 4.13). When E=0, the bottom display of the controller
will alternately display the SV and the activated alarm parameter.
5) Activate the AL1 and AL2 by time instead of temperature
For the controllers with the ramp and soak function (SYL-2342P and SYL-
2352P), AL1 and AL2 can be activated when the process reaches a specific
time. This is discussed in the section 3.7 of “Supplementary Instruction Manual
for ramp/soak option.
4.4.2 Hysteresis Band “Hy”
The Hysteresis Band parameter Hy is also referred as Dead Band, or
Differential. It permits protection of the on/off control from high switching
frequency caused by process input fluctuation. Hysteresis Band parameter is
used for on/off control, 4-alarm control as well as the on/off control at auto
tuning. For example: 1) When controller is set for on/off heating control mode,
the output will turn off when temperature goes above SV+Hy and on again
when it drops to below SV-Hy. 2) If the high alarm is set at 800 °F and
hysteresis is set for 2 °F, the high alarm will be on at 802 °F (ALM1+Hy) and
off at 798 °F (ALM1-Hy).
Please note that the cycle time can also affect the action. If the temperature
passes the Hy set point right after the start of a cycle, the controller will not
respond to the Hy set point until the next cycle. If cycle time is set to 20
seconds, the action can be delay as long as 20 seconds. Users can reduce
the cycle time to avoid the delay.
tuning from the front panel is inhibited to prevent accidental re-starting of the
auto tuning process. To start auto tuning again, set At=1 or At=2.
4.5 Control action explanations
4.5.1 PID
Please note that because this controller uses fuzzy logic enhanced PID
control software, the definition of the control constants (P, I and d) are
different than that of the traditional proportional, integral, and derivative
parameters.
In most cases the fuzzy logic enhanced PID control is very adaptive and may
work well without changing the initial PID parameters. If not, users may need
to use auto-tune function to let the controller determine the parameters
automatically. If the auto tuning results are not satisfactory, you can manually
fine-tune the PID constants for improved performance. Or you can try to
modify the initial PID values and perform auto tune again. Sometimes the
controller will get the better parameters.
The auto-tune can be started in two ways. 1) Set At=2. It will start
automatically after 10 seconds. 2) Set At=1. Then you can start the auto-tune
any time during the normal operation by pressing the A/M key. During auto
tuning, the instrument executes on-off control. After 2-3 times on-off action,
the microprocessor in the instrument will analyze the period, amplitude,
waveform of the oscillation generated by the on-off control, and calculate the
optimal control parameter value. The instrument begins to perform accurate
artificial intelligence control after auto tuning is finished. If you want to exit
from auto tuning mode, press and hold the (A/M) key for about 2 seconds
until the blinking of "At" symbol is stopped in the lower display window.
Generally, you will only need perform auto tuning once. After the auto tuning
is finished. The instrument will set parameter “At” to 3, which will prevent the
(A/M) key from triggering auto-tune. This will prevent an accidental repeat of
the auto-tuning process.
(1) Proportional constant “P”
Please note the P constant is not defined as Proportional Band as in the
traditional model. Its unit is not in degrees. A larger constant results in larger
and quicker action, which is the opposite of the traditional proportional band
value. It also functions in the entire control range rather than a limited band.
If you are controlling a very fast response system (>1 °F/second) that fuzzy
logic is not quick enough to adjust, set P=1 will change the controller to the
traditional PID system with a moderate gain for the P.
(2) Integral time “I”
Integral action is used to eliminate offset. Larger values lead to slower action.
Increase the integral time when temperature fluctuates regularly (system
oscillating). Decrease it if the controller is taking too long to eliminate the
temperature offset. When I =0, the system becomes a PD controller.
(3) Derivative time “D”
Derivative action can be used to minimize the temperature over-shoot by
responding to its rate of change. The larger the number, the faster the action.
4.4.3 Control mode “At”
At=0 On/off control. It works like a mechanical thermostat. It is suitable for
devices that do not like to be switched at high frequency, such as motor and
valves. See 4.5.2 for details.
At=1 Gets the controller ready to start the Auto tuning process by pressing the
A/M key.
At=2 Start auto tuning. The function is the same as starting auto tuning from
front panel.
At=3 This configuration is automatically set after auto tuning is done. Auto
4.5.2 On/off control mode
It is necessary for inductive loads such as motors, compressors, or solenoid
valves that do not like to take pulsed power. It works like a mechanical
thermostat. When the temperature passes the set point, the heater (or
cooler) will be turned off. When the temperature drops back to below the
hysteresis band (Hy) the heater will turn on again.
To use the On/off mode, set At=0. Then, set the Hy to the desired range
based on control precision requirements. Smaller Hy values result in tighter
temperature control, but also cause the on/off action to occur more
frequently.
PV
SV
SV-Hy
100
97
Relay On
When heating, At=0
If PV
≤
(SV-Hy), relay on
If PV
≥
(SV+Hy), relay off
(SV=100, Hy=3)
Figure 5. On/off control mode
SV+Hy
103
