LEESON Micro Series Compact Inverters - Manual (Page 80)

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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