Rockwell Automation 1746-BLM Blow Molding Module Installation Instructions - Manual (Page 8)

8 Blow-molding Module
Publication 1746-IN014B-EN-P - January 2001
Module’s microprocessor
The module processor is a 16-bit fixed-point digital signal processor (DSP). It
communicates with the analog I/O channels over a high speed (2MHz) full-duplex
synchronous serial link. Serial connection between the processor and analog I/O
hardware facilitates electrical isolation. Digital I/O is performed in a similar fashion.
The module processor manages all communications between the module and the
SLC processor. It performs such functions as interpolation between profile
setpoints, loop tuning, and calculation of calibration coefficients in addition to
executing the control algorithm.
Module’s PID control algorithm
For servo control, the module uses a Proportional + Integral + Derivative algorithm
with anti-windup, high-frequency derivative gain limiting and setpoint weighting.
Anti-windup is achieved by modeling the actuator (normally a valve amplifier) as a
nonlinear device that operates linearly over a limited range, beyond which it
saturates.
An additional error signal is formed by taking the difference of raw controller
output, v(n), and control output, u(n), which is clamped at the actuator saturation
limits. This signal is multiplied by gain 1/Tt, where Tt is called the integrator
tracking time and summed into the integral term. High-frequency derivative gain
limiting lets you compensate for derivative term susceptibility to high frequency
noise. Setpoint weighting provides a mechanism for independent tuning of setpoint
and load response.
Digital I/O
There are four fully isolated digital inputs on the module. They are of the
current-sinking type. Their primary use is for start-of-parison-drop synchronization
on continuous extrusion machines. The digital inputs may be used as general
purpose inputs if the start of drop synchronization feature is not needed.
There are four isolated digital outputs on the module. They are of the
open-collector (current-sinking) type and share a common 24VDC (nominal)
external power supply. Their primary use is as profile step-synchronization
indicators. The digital outputs may be used as general purpose outputs if the step
synchronization feature is not needed. See page 41 for complete specifications.
Analog I/O
There are four analog I/O channels on the module. Each channel consists of a
14-bit analog-to-digital converter and a 14-bit digital to analog converter. As a
group, the four I/O channels and excitation output are optically isolated from the
remainder of the module. The high common mode input range of the input
amplifiers and the isolated nature of LVDTs and linear potentiometers make it
unnecessary to isolate the channels from one another. See page 41 for complete
specifications.