Chapter 4 Block Reference
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National Instruments Corporation 4-5 FieldPoint FP-3000 User Manual
PID Control
In a Fieldbus network, a PID control loop is composed of three function
blocks: an Analog Input (AI) block, a Proportional Integral Derivative
(PID) block, and an Analog Output (AO) block. Figure 4-1 shows all three
blocks and the interconnections between the blocks. The PID block’s IN
parameter is connected to the AI block’s OUT parameter. The PID uses this
linkage to determine the current value of the process variable it is
controlling. The PID uses linkage from the PID’s OUT parameter to the AO
block CAS_IN parameter to adjust the AO block setpoint. To allow the
cascade to be correctly initialized, a third back calculation linkage is
created that allows the AO block to send its current setpoint back up to the
PID block. These linkages must be established by using a PC-based
Fieldbus configuration system, such as the NI-FBUS Configurator. For
more information, refer to Example 2: Temperature Control with the
FP-3000 in Chapter 3, Example Application s.
Table 4-2. Function Blocks and FieldPoint Modules
Channel Type Supported
Module Block Type
Analog Input FP-AI-100 Fp Ai 100
FP-AI-110 Fp Ai 110
FP-AI-111 Ap Ai 111
FP-TC-120 Fp Tc 120, Fp Tc 120 C
FP-RTD-122 Fp Rtd 122
Analog Output FP-AO-200 Fp Ao 200
FP-PWM-520 Fp Pwm 520
Discrete Input FP-DI-300 Fp Di 300
FP-DI-301 Fp Di 301
FP-DI-330 Fp Di 330
Discrete Output FP-DO-400 Fp Do 400, Fp Cdo 400
FP-DO-401 Fp Do 401, Fp Cdo 401
FP-RLY 420 Fp Rly 420, Fp Crly 420