6. Function blocks
6.1 Manufacturer function blocks
the actual value (Xi) at a specified scan time. The equation used by the device for the
proportional component is as follows:
YP(t) = Kp * [Xs(t) - Xi(t)]
Kp =
Proportional gain
Xs(t) =
SETPOINT value at scan time t
Xi(t) =
ACTUAL value at scan time t
Integral component
The integral component YI is proportional to the sum of the control difference over
time. The equation used by the device for the integral component is as follows:

YI(t) = Kp * Tc / Tn * [Xs(t) - Xi(t)] + YI (t-1)]


K
p
= Proportional gain
Tc = Scan time
Tn = Reset time (also known as integration
time).
Xs(t) = Setpoint with scan time t
Xi(t) = Actual value with scan time t
YI(t–-1)= Value of the integral component of the
manipulated variable with scan time t – 1

Differential component
The differential component YD is proportional to the change in the control difference.
So as to avoid step changes or jumps in the manipulated variable caused by the dif-
ferential behavior when the setpoint is changed, the change of the actual value (the
process variable) is calculated and not the change in the control difference. This is
shown by the following equation:

YD(t) = Kp x Tv / Tc x (Xi (t-1) - Xi(t))


K
p
= Proportional gain
Tc = Scan time
Tv = Rate time of the control system (also called
the differential time)
Xi(t) = Actual value with scan time t
Xi(t-1) = Actual value with scan time t - 1

In order for a PID controller to work, it must be enabled with DC_EN =1. The PID con-
troller will provide manipulated variable QV as an output variable. If the function
block input EN is not active, the entire PID controller will be disabled and reset. The
manipulated variable at the QV output will assume a value of 0. Function block inputs
DC_EP, DC_EI, and DC_ED all need to be active in order for the proportional term,
integral term, and derivative term to be calculated.
easyE402/24 MN050009ENEaton.com
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