Siemens 505-2557 User Manual
Advanced Function Programming
3-2
SIMATIC 505–2557 Installation and Operation Guide
3.1
Advanced Software Functions
As PLC control systems become more complex, the need for real-time
processing of analog signals is needed at the I/O level. Current
implementations using the 505 controllers utilize analog alarm blocks
and/or special function programs within the controller. The SIMATIC
505–2557 analog input module from Siemens Energy & Automation, Inc.,
can reduce the program complexity and scan time by performing this signal
processing in the module.
processing of analog signals is needed at the I/O level. Current
implementations using the 505 controllers utilize analog alarm blocks
and/or special function programs within the controller. The SIMATIC
505–2557 analog input module from Siemens Energy & Automation, Inc.,
can reduce the program complexity and scan time by performing this signal
processing in the module.
Scaling, alarming, peak/valley hold, digital filtering, and averaging are
available on a per-channel basis and are selected through a simple PLC
configuration routine. When these advanced functions are enabled, the
module logs in as 16X / 16Y / 32WX / 32WY. A jumper on the module selects
the standard 16WX login or the high-density advanced function interface.
available on a per-channel basis and are selected through a simple PLC
configuration routine. When these advanced functions are enabled, the
module logs in as 16X / 16Y / 32WX / 32WY. A jumper on the module selects
the standard 16WX login or the high-density advanced function interface.
Each of these functions can be selected on a per-channel basis, and each
channel can have any function in any combination, e.g. alarming on a scaled
value which is digitally filtered and set for peak hold. (See Section 3.4 for
timing considerations.)
channel can have any function in any combination, e.g. alarming on a scaled
value which is digitally filtered and set for peak hold. (See Section 3.4 for
timing considerations.)
Scaling
Each channel can be configured with low and/or high scale value.
A flowmeter that outputs 0 mA @ 5 cfm and 20 mA @ 50 cfm would have a
low scale of 5 and a high scale of 50. An operator interface attached to the
controller could then read the analog values directly in engineering units
without having to run a Special Function program to scale the input.
low scale of 5 and a high scale of 50. An operator interface attached to the
controller could then read the analog values directly in engineering units
without having to run a Special Function program to scale the input.
Alarming
Each channel can be assigned a low and/or high alarm value.
No analog alarm blocks are needed in the controller. Alarming occurs
real-time as the signal is processed by the module. Two WX words are used
to indicate high and low alarm conditions (bit 1 = channel 16, etc.). A third
WX word is the logical OR of the high and low alarms.
real-time as the signal is processed by the module. Two WX words are used
to indicate high and low alarm conditions (bit 1 = channel 16, etc.). A third
WX word is the logical OR of the high and low alarms.
Peak/valley hold
The peak or valley of a rapidly changing analog signal
has been impossible to detect unless an external circuit was used. The
SIMATIC 505–2557 makes possible the detection of a peak or valley and
holds that value until reset by the controller. The peak/valley measurement
is available to the controller at the same time as the currently measured
analog value.
SIMATIC 505–2557 makes possible the detection of a peak or valley and
holds that value until reset by the controller. The peak/valley measurement
is available to the controller at the same time as the currently measured
analog value.
Averaging
This option is used to “clean up” a signal that is at a steady
state, e.g., a sensor riding on a liquid tank with riplets. The user specifies
how many signal scans to average and this value is presented to the
controller.
how many signal scans to average and this value is presented to the
controller.
Digital filtering
This has the effect of a moving average operation
(actually it is an Infinite Impulse Response filter), and is useful to smooth
out the high frequency noise on a changing analog signal. See Section 3.4.
out the high frequency noise on a changing analog signal. See Section 3.4.
Introduction
Overview of the
Advanced
Functions
Advanced
Functions