CNT-APG002-EN 23
®

Chapter 3

Programming PID loops
This chapter presents programs written in process control language
(PCL) and the Tracer graphical programming (TGP) editor. This chapter
does not discuss how to use the PCL or TGP editors. For information on
using these editors, refer to Universal Programmable Control Module
(UPCM) Programming Guide (EMTX-PG-5), Programmable Control Mod-
ule (PCM) Edit Software Programm ing Guide (EMTX-PG-6), and Tracer
Graphical Programming applications guide (CNT-APG001-EN).

Programming in PCL

PID control is called direct digital control (DDC) in process control lan-
guage (PCL). Table5 shows how the DDC function is invoked in PCL. In
this example, DDC loop 4 compares the discharge-air temperature to the
heating discharge-air setpoint. Line 1 stores the result of the PID func-
tion in the analog variable HEATCALC. Line 2 controls the valve to the cal-
culated value. You can program specific PID settings in the DDC Loop
Parameters screen, shown in Table6 on page 24.
Table 5: PID (DDC) loop in PCL
Line Result 1st Arg Operator 2nd Arg Description of Statement
---- -------- ----------- -------- ----------- ---------------------------------
1 HEATCALC = DISCHTMP DDC:4 HEATSP DDC loop 4 compares heat setpoint
to discharge-air temp
2 HEATVLV = CONTROL HEATCALC Output controlled to HEATCALC
value
Result:
analog variable
Measured variable:
analog input
analog variable
Setpoint:
analog input
analog variable
analog setpoint
analog parameter
Loop name