National Instruments 371685C-01 用户手册

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The actual controller output is limited to the range specified for control output, as follows:

and

The following formula shows the practical model of the PID controller.

The PID functions use an integral sum correction algorithm that facilitates anti-windup and 
bumpless manual-to-automatic transfers. Windup occurs at the upper limit of the controller 
output, for example, 100%. When the error (e) decreases, the controller output decreases, 
moving out of the windup area. The integral sum correction algorithm prevents abrupt 
controller output changes when you switch from manual to automatic mode or change any 
other parameters.

The default ranges for the SP, PV, and output parameters correspond to percentage values; 
however, you can use actual engineering units. If you use engineering units, you must adjust 
the corresponding ranges accordingly. The T

 and T

 parameters are specified in minutes. 

In manual mode, you can change the manual input to increase or decrease the output.

All the PID control functions are reentrant. Multiple calls from high-level functions use 
separate and distinct data.

As a general rule, manually drive the PV until it meets or comes close to the SP 

before you perform the manual-to-automatic transfer.

Gain scheduling refers to a system in which you change controller parameters based on 
measured operating conditions. For example, the scheduling variable can be the SP, the PV, 
a controller output, or an external signal. For historical reasons, the term gain scheduling is 
used even if other parameters, such as the derivative time or integral time parameters, change. 
Gain scheduling effectively controls a system whose dynamics change with the operating 
conditions.

if u k

( ) u

then  u k

( ) u

=

≥

if u k

( ) u

then  u k

( ) u

=

≤

( )

–

(

)  

1

----

(SP PV)dt T

d 

------------

–

–

0

∫

+

=