Allen-Bradley ProcessLogix 1756-IA16, Справочное руководство, Страница: 86 / 120

Publication 1757-RM810A-EN-P - May 2002
3-46 Functional Blocks
PULSELENGTH
Description Generates pulse trains according to its pulse length control algorithm. The pulsed outputs are usually fed to Digital
Output Channel blocks.
Dual Pulse Length: A control algorithm turns on either a “raise” channel or a “lower” channel after every execution of
this algorithm. The selected output stays on for a time period that is calculated by the control algorithm. The
calculated on-duration will be in 10 msec increments.
Single Pulse Length: A single output channel is used to indicate the direction (raise or lower) of the actuator. A
second output channel is used to indicate the calculated on-duration (or length) of the pulse. The calculated
on-duration will be in 10 msec increments.
Function
•
Typically used in conjunction with a POSPROP block to step a valve open or closed, raise or lower a rotary device,
or move the plates of a pulp mill refiner together or apart.
•
The POSPROP block feeds the PULSETIME input parameter to the PULSELENGTH block. This parameter is an
internal structure that contains the pulse width specification (in seconds). It also contains a Serial Number that
changes every time there is a new pulse width value. The PULSELENGTH block checks for a change in the Serial
Number before reacting to the pulse width specification.
Inputs
•
Requires a pulse time (PULSETIME) input from another block. A POSPROP block usually supplies this.
•
The PDELAYDIRCHG input is user configurable in seconds.
•
The optional LOCALMAN input should come from another block in a logic strategy where an ON condition means
that the CEE is not controlling the output of the device.
Outputs The PULSELENGTH block has the following initializable outputs:
•
PORAISE = Pulse output for Raise pulses. These pulses are generated if the pulse width specified by the
PULSETIME input is positive.
•
POLOWER = Pulse output for Lower pulses. These pulses are generated if the pulse width specified by the
PULSETIME input is negative.
•
PO = Pulse output for both Raise and Lower pulses. These pulses are generated as a logical OR between the
PORAISE and POLOWER pulses.
•
PODIR = Direction for PO. This output is OFF for a Lower pulse and is ON for a Raise pulse.
Parameters ALMDB
ALMDBU
ALMTM
INITMAN
INITREQ LOCALMAN
ORDERINCM
PDELAYDIRCHG
PO
PODIR POLOWER
PORAISE
PULSETIME