Hitachi WJ200-001S Instruction Manual page 279

472
To use the PID Second Stage Output feature, you will need to choose upper and lower
limits for the PV, via
these are the thresholds Stage #1 inverter uses to turn ON or OFF Stage #2 inverter
via the [FBV] output. The vertical axis units are percent (%) for the PID setpoint, and
for the upper and lower limits. The output frequency, in Hz, is superimposed onto the
same diagram.
When the system control begins, the following events occur (in sequence in the timing
diagram):
1. Stage #1 inverter turns ON via the [FW] Run command.
2. Stage #1 inverter turns ON the [FBV] output, because the PV is below the PV low
limit . So, Stage #2 is assisting in loop error correction from the beginning.
3. The PV rises and eventually exceeds the PV high limit . Stage #1 inverter then
turns OFF the [FBV] output to Stage #2, since the boost is no longer needed.
4. When the PV begins decreasing, only Stage #1 is operating, and it is in the linear
control range. This region is where a properly configured system will operate most
often.
5. The PV continues to decrease until it crosses under the PV low limit (apparent
external process disturbance). Stage #1 inverter turns ON the [FBV] output, and
Stage #2 inverter is assisting again.
6. After the PV rises above the PV low limit, the [FW] Run command to Stage #1
inverter turns OFF (as in a system shutdown).
7. Stage #1 inverter enters Stop Mode and automatically turns OFF the [FBV] output,
which causes Stage #2 inverter to also stop.
PV high limit
PID setpoint (SP)
PV low limit
[FBV] to Stage #2 [FW]
The terminal [FBV] configuration table is on the following page.
and
 
%/Hz
Output frequency


Stage #1 [FW] 1
0
1
0
Events: 1,2
respectively. As the timing diagram below shows,
PID feedback (PV)
3 4 5 6 7
t