Specifications
28
DFB design
(cont’d)
3 Control I/Os
This group gathers process data inputs and outputs (I/O ) used to control the device. I/O scanning, based
on periodic read / write variables, allows implicit exchanges of modiable data. This functionality should be
reserved for frequently used variables; access to other variables is by explicit exchanges.
I/O Scan Input (Structure)
Fb_Stat Starter status word. Feedback signal from I/O scanning
Fb_RPM (*) Variable speed drive output speed. Feedback signal from I/O scanning
FB_Meas (*) Starter measures. Feedback signal from I/O scanning The number of
measurements depends on the device type and content to set up.
I/O Scan Input (Structure)
Q_Crtl Starter control word, sent to the starter via I/O scanning
Q_RPM (*) Variable speed drive setpoint speed, sent to starter via I/O scanning
(*) Those parameters are available only on variable speed drive
4 Parameters assigment
These variables are related to the device operating mode. As they are not written as constant parameter in
PLC memory, they should be saved in another way. Otherwise, on a PLC cold start all adjusted parameters
would be lost.
To overcome that, we can save the parameter's current value as initial value; the following procedure could be
applied:
Step Action
A Under Unity, validate the “save” attribute of all device parameter variables
B Adjust device parameters at the desired value from Unity
C With Unity, on-line mode, set system bit %S94 to 1: Initial values of all variable
marked with the “save” attribute will be replaced by their current values
D Save the application (on M340, it is necessary, in addition, to set %S66 to 1 or to
transfer the RAM application to the memory card).
Following this procedure, when a PLC cold start occurs, all device parameters will be initialized with the last
adjusted values.
Those DFB input parameters should be adjusted during start-up of the installation (by assigning constant value
to the variables). Some of those parameters are sent to HMI or SCADA for visualization only.
Param (Structure)
Discrepancy_time Max time between an order and the right feedback
Min_time_Stop Minimum time between stop and restart
3-Application design
Software design