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Settings
Touch the Settings icon to view or change the settings related to the relay.
Set point
Enter the sensor process value at which the output will pulse at the Minimum Output % set below.
Proportional Band
Enter the distance that the sensor process value is away from the set point beyond
which the output will be pulsing at the Maximum Output % set below.
Minimum Output
Enter the lowest possible pulse rate as a percentage of the Maximum Stroke Rate set
below (normally 0%).
Maximum Output
Enter the highest possible pulse rate as a percentage of the Maximum Stroke Rate set below.
Maximum Rate
Enter the maximum pulse rate that the metering pump is designed to accept (10 - 2400
pulse/minute range).
Input
Select the sensor to be used by this relay.
Direction
Set the control direction.
5.3.10
Relay, PID Control Mode
ONLY AVAILABLE IF CONTROLLER INCLUDES PULSE OUTPUT HARDWARE & HVAC MODE IS DISABLED
The PID algorithm controls a solid state relay using standard Proportional-Integral-Derivative control logic. The
algorithm provides feedback control based on an error value continuously calculated as the difference between a
measured process variable and a desired set point. Tuning settings specify the response for proportional (the size of
the error), integral (the time that the error has been present), and derivative (the rate of change for the error) param-
eters. With proper tuning, the PID control algorithm can hold the process value close the set point while minimiz-
ing overshoot and undershoot.
Normalized Error
The error value versus set point that is calculated by the controller is normalized and represented as percent of full
scale. As a result, tuning parameters entered by the user are not dependent upon the scale of the process variable
and the PID response with similar settings will be more consistent even when using different types of sensor inputs.
The scale used to normalize the error is dependent upon the type of sensor selected. By default, the full nominal
range of the sensor is used. This range is editable by the user if tighter control is desired.
PID Equation Formats
The controller supports two different forms of the PID equation as specified by the Gain Form setting. The two
forms require different units for entry of the PID tuning parameters.
Standard
The standard form is more commonly used in industry because its time-based settings for the integral and deriva-
tive coefficients are more meaningful. This form is selected by default.
Parameter
Description
Units
K
p
Gain
unitless
T
i
Integral Time
seconds or seconds/repeat
T
d
Derivative Time
seconds
Output (%) = K
p
e(t) +
f
e(t)dt + T
d
de(t)
dt
1
T
i
Parameter
Description
Units
e(t)
Current Error
% of full scale
dt
Delta Time Between Readings
seconds
de(t)
Difference Between Current Error & Previous Error
% of full scale
Parallel
