YSI 5200A - Manual (Page 70)

YSI 5200A
139
YSI 5200A
138
PID
(Proportional, Integral, and Derivative ) /
PWM (Pulse, Width, Modulation) Control
PID/PWM control menu options are shown below for an aux analog system.
PID/PWM Control uses a complex algothrium in determining the best way to sustain
water system value(s) around a set point. PID/PWM control is a feed back control
system. Three factors determine how PID/PWM control seeks to maintain water
system value(s) around a set point. The three factors are:
-the error (distance) from present measurement of input to set point (present time);:
-the duration of the error (accumulation of past errors)
-the speed at which the value is approaching the set point (predicts future errors) ;
The PID/PWM control system is considered active whenever error exists away from
the configured set point. (See PID/PWM up/down control configuration - page
139). The PID/PWM control system is flexible and can be tuned to keep water
systems around their set points even though the environment is exposed to distur-
bances that drive the input value away from set point. An example of a PID/PWM
control system that most readers will be familiar with is a cruise control system in
a car. Acceleration and deacceleration adjustments are continually being made to
maintain the car at a constant speed or set point.
Configure PID/PDW control systems at Sensor Setup menus.
PID/PWM control also allows configuration of high and low alarm systems to
activate peripheral devices and/or to provide alarm notification messages when
alarm condition(s) exist.
Notes:
- Changing control method between PID/PWM and Set Point may result
in invalid setp point, control and alarm value configurations. Always
reconfirm sensor setup system menu configuration when control mode
is changed.
- PID/PWM control is not available for aux digital systems.
Configuring the 5200A
- DO system(s) PID/PWM set point can be configured using either mg/L
or %Sat set point.
PID/PDW Tuning
Each and every water system responds very differently to peripheral control de-
vices due to many factors. Factors that can influence the ability of a control device
to maintain a certain set point include size of system, peripheral equipment such
as pumps, lighting, system location and the like. While PID/PWM tuning is an
important and necessary requirement to properly configure the control system
it is outside the scope of this document to describe the tuning process. There is a
wealth of information available on the www as well as in print. Please familiarize
yourself with additional information in order to further your understanding of the
PID/PWM control method.
Set Point
Configure the set point to be the value at which you’d like the system to ideally
operate at. DO set point can be configured in either mg/L or %Sat at the. Configure
at PID mode menu.
Control Up/Down
Configure the PID/PDW control system to either control up (Falling, to create a
control action to reduce down the system water parameter value) or control down
(Rising, to create a control action to increase up the system water parameter value).
A PID/PDW control can be used only to control the system by either driving the
system value up or down. A PID control cannot be used to drive the system value
both up and down.
PID/PWM Control Actions
Interval, Gain, Reset Interval
Configuration of three control actions allows for greater control and stablity of
a particular environment. The control actions are Gain (page 140), Reset/Inteval
(page 140) and Interval (page 140). These three controls actions are closely inter-
related in terms of how the PID/PWM algothrium works. The objective is to tune
and configure these control actions in order that the corrective action (output con-
trol on time) performed by the 5200A results in system stability. That is, the system
will hold the set point without oscillating wildly (overshooting or undershooting
by significant amounts) over and under the set point. A large amount of ocillation
could cause irreparable damage to the system by dosing too large an amount, or too
small an amount, of a control dosing additive to the system stream.
Configuring the 5200A