User guide

 Forareverseactingtransducer,setParameter75-FB@MINtothemaximumprocessvariablefeedback
value,andsetParameter76-FB@MAXtotheminimumprocessvariablefeedbackvalue.Inotherwords,
Parameter75issethigherthanParameter76.Seetheexamplebelow:
Example 2: A 0-100 psi transducer outputs a 20 mA signal at 0 psi and 4 mA at 100 psi. Program Parameter
75 to 100.0 PSI, and Parameter 76 to 0.0 PSI (This assumes that Parameter 31 - UNITS is set to pid PSI,
andParameter33-UNITSDPissettoXXX.X).
19.2 THE SYSTEM - DIRECT AND REVERSE ACTING
The entire system can also be direct or reverse acting. In a direct acting system, an increase in motor speed
causes anincreasein the process variable. This isequivalentto requiring an increase in motorspeedin
responsetoadecreasingprocessvariablefeedback.
In a reverse acting system, an increase in motor speed causes a decrease in the process variable. This is
equivalenttorequiringanincreaseinmotorspeedinresponsetoanincreasingprocessvariablefeedback.
Examplesofdirectandreverseactingsystemsaredescribedinthenextsection.
19.3 PID CONTROL - DIRECT AND REVERSE ACTING
The PID Set point Control software can be direct or reverse acting, and must be set to match the system.
ThisisaccomplishedwithParameter70-PIDMODE.WhensettoNORMAL(fordirectactingsystems),
thePIDunitwillcommandanincreaseinmotorspeedif theprocessvariablefeedbackdecreases,anda
decrease in motor speed if the process variable feedback increases. When set to REVERSE (for reverse
actingsystems),theoppositeistrue.
NOTE: The REVERSE setting for Parameter 70 - PID MODE is not used to compensate for reverse
acting feedback devices. If a reverse acting feedback device is used, program Parameters 75 and 76 as
described above.
 An example of a direct acting system is one that maintains duct pressure. Duct pressure is the process
variablethatismonitoredbythefeedbackdevice.Asductpressurerises,motorspeedneedstobedecreased
to maintain the pressure. A direct acting PID control will command a decrease in motor speed in response
toanincreasingprocessvariablefeedback.
 Anexampleofareverseactingsystemisonethatmaintainswatertemperatureinacoolingtower.Water
temperatureistheprocessvariablethatismonitoredbythefeedbackdevice.Asthewatertemperaturerises,
motor speed needs to be increased to lower the temperature of the water. A reverse acting PID control will
commandanincreaseinmotorspeedinresponsetoanincreasingprocessvariablefeedback.
19.4 SET POINT REFERENCE SOURCES
The set point reference input can be one of the following:
1. Keypad
2. 4-20 mA signal at TB-5B
3. 0-10 VDC signal at TB-5A
4. Potentiometer signal at TB-5A
In order to use TB-5A or TB-5B for a set point input, one of the terminals must be programmed for the
appropriate signal. Closing the TB-13 terminal to TB-2 will then select that signal as the set point reference.
IfthecontactclosureisnotmadetoTB-2,thesetpointreferencesourcewilldefaulttothekeypad.See
Parameters 47 - TB13A, 48 - TB13B, and 49 - TB13C.
Remote set point reference inputs at TB-5A and TB-5B can only be used if that terminal is NOT being
usedfortheprocessfeedbacksignalfromatransducer.TheMICROSerieshasonlyoneanaloginputof
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