Cheetah Pregius Camera with 10 GigE Vision Interface – User Manual
October 8, 2020
Page
117
of
170
Rev 1.0
P, I, and D Coefficients
The P (Proportional), I (Integral), and D (Derivative) coefficients of PID feed-back control loops
determine speed and stability of AEC and AGC algorithms.
A PID controller continuously calculates a difference (an error) between a setpoint (SP)—
ExposureGainAutoTarget
— and a process variable (PV)—
AverageLuminosity
. Based on the sum
of proportional, integral, and derivative responses, the controller determines an output value
and adjusts exposure or gain to minimize the error. The PID controller continuously varies the
output value until the luminance reaches the setpoint.
setpoint
(
ExposureGainAutoTarget
)
PID
image sensor
process variable
(
AverageLuminosity
)
AEC/AGC
feedback
output value u(t)
y(t)
The AGC algorithm uses all three responses with a manual control available over the P, I, and D
coefficients.
setpoint
(
ExposureGainAutoTarget
)
Pcoef
x
e(t)
feedback y(t)
output value u(t)
∑
- +
Dcoef
x
(e
n-1
– e
n
)
∑
+
error e(t)
+
+
The AEC algorithm uses only two responses – proportional and derivative with a manual control
available over the P coefficient only.
AEC/AGC
PID coefficients controls
AEC
P varies depending on exposure
I = 0
D = P/2
AGC
P, I, and D are fixed values
Icoef
x
∑
e
𝑛𝑛
𝑖𝑖=1
n
Pcoef
x
e
n
Dcoef
x (
e
n-1
- e
n
)
error e
n
