Data
acquisition with SAIA-PCD
You need to collect history
data in a PCD system to create reports, trends, statistics or archive files.
This is a typical task knowing when you start but not when you'll finish. You
should also expect surprise and difficulties to get a proper and stable
solution. You may also run in a endless process if you
do not exactly know what you need and what you can do.
A main cause of
difficulties is due to the fact that the usual programming of a PCD, including
the S-Bus communication driver, is based on the principle of process data
permanently refreshed in the PCD and over the communication network. The notion
of buffering, time-stamping and transfer of data packages is missing.
This document attempt to
help you by making a good choice of the basic functions and tools to use and
will show some limits of the various solutions.
To segregate this approach
of data acquisition, 6 possible cases are presented. Each of them start on a
different based and will lead to more or less performances, flexibility and
reliability. The three first solutions uses only SAIA's Fbox libraries, while the last 3 are Engiby's solutions.
1. Using the DB Logger Fbox
2. Using the Data buffer
Fbox family
3. Using the Data buffer for
the Web Server
4. The NG-Dump software
5. The NG-Trace software
6. The NG-Data package
The aspects to be discussed
and compared are like:
·
Investment
in money
·
Engineering
work
·
Sampling
signal
·
Time
stamping
·
Data
identification
·
Buffer
loading
·
Buffer
unloading
·
Data
package reception
·
Handling
of communication errors
·
Stability
and reliability of the solution
·
Modifications/Extensions
Using the DB-Logger Fbox
This Fbox is part of the
standard S-Fup Fbox families and therefore doesn't
need any supplementary investment. A simple test program will work very
quickly. You will also reach the same result with a simple IL program using the
TFR instructions.
First difficulties will
appear to correctly handle the pointers at start up, after power down and when
the buffer overflows. Data sampling, identification and time stamping is under
your own responsibility. The download of the buffer via modem is very difficult
as you have to care at all possible errors with the PSTN network. A correct
data queuing in all cases is almost impossible.
The unloading must be fully
programmed in a SCADA system or by your own application.
In conclusion, this
solution is good and fast for a simple application with low demand on
reliability. It assumes that you are ready to make all necessary effort on the
reception side to reach the required level of reliability. Maintenance and
extensions are not easy because a complex PCD program need to be modified and
the application on the other side also need a reprogramming.
Data Buffer Fbox family
This Fbox family is
included in the Modem library and bound to a rather low investment. The buffer
loading in the PCD is simple to realize.
The local pointer is
handled by the Fbox. Data are identified by there PCD address and time stamping
is included. The sampling is still under your responsibility. The buffer
delivers some useful information like buffer load level, overflow signal and
internal errors.
The buffer unloading however, must be realized by the SCADA system or by your
self-programmed solution. Two solutions are possible:
- A direct access to the Data block which allows you the unloading of all
records in one go.
- The use of the read Buffer Fbox which unload the records one by one via a
register block.
Your task would be easy if the S-Bus driver of the SCADA already include the
handling of this Data Buffer.
In conclusion, this
solution is good to quickly acquire some data in the PCD but you must provide
important effort for the data reception and storing. The reliability will
depend on your ability to handle the data reception including error handling.
This task may be rather complex when modem connections are involved.
Maintenance and extensions are simple on the PCD side because you can mix up
many variables in the same buffer. An important adaptation on the SCADA side is
however required.
Data Buffer of the Web
Server
Three solutions exist within
this package.
- The Online trending
- The Offline trending
- The Visi+ data transfer
The online trending is not
really a data acquisition solution and is not considered in this discussion. The
Visi+ solution is limited to Visi+
and therefore also not included in the comparison.
This Fbox family is available
for free with PG5 SAIA but the view with the Web editor requires an advanced license.
The integration in a PCD is quite simple thanks the availability of Fboxes. A supplementary work is necessary to create the Web
pages and establish the correct relation.
A restriction is that the
buffer has a limited length and old data will be overwritten or recording is
stopped when the buffer is full. The automatic transfer of data over Modem or
Ethernet to a PC remains a complex task. The reliability is fully under your
responsibility.
As standard solution, the recorded
data remains in the PCD memory and you must establish a connection to the Web
Server to view the recorded data. It is however possible to manually save a
buffer content in CSV file on the PC running the Web browser.
Finally, the solution is a good
debugging solution but is not suitable for data acquisition on a central server
for long time recording. The main advantage remains the possibility to view the
data from any PC on the LAN with a simple Web browser.
NG-Dump software
The NG-Dump is a Windows
program created to dump data from a SAIA-PCD system to Excel or CSV-files in a
very simple way. The only investment to plan is the license price of the
software itself. No special PCD programming is required.
The recording interval, the
data addresses and all necessary parameters are set in the software. The data
reading and the time stamping is ensured by the software itself. This is a big
comfort but the result is that a permanent PCD connection is required to ensure
a continuous recording. The PCD has no autonomy, which means that data records
are lost in case of connection break down or when the PC is not running.
The data can be read over
point-to point, S-Bus, or Ethernet connection. Simply, any PG5 connection can
be used. Modem should only be used for single shot reading.
In conclusion, this is a
very interesting solution when one can ensure a continuous function of the PC and
the PCD connection, or if the data integrity is not an important point.
NG-Trace software
The NG-Trace is a PG5
Add-On Toll that allows you to configure the data buffer, to download and
display the recorded data. It allows several type of implementation at different
price levels starting from a freeware version.
You don't have to care
about sampling signals. Time stamping and data are identified with a clear
text. The buffer is a rotary buffer and can be unloaded in real time or at
later time over point-to point, S-Bus, modem or Ethernet connection. Simply,
any PG5 connection can be used.
The unloaded data can be
viewed in a spread sheet, in graphical form or can be exported to an excel file
in one click.
In conclusion, the NG-Trace
is rather a debugging tool optimized to run in the PG5 environment. Maintenance
and extensions are simple because each modification is immediately overtaken on
both sides (PCD program and online view). This solution is however not suitable
to build long time data storage because the queuing of packages is not included.
Reliability is not a point of discussion because the buffer unloading and
storing is a user operation.
NG-Data
The NG-Data package is made
of Fboxes for the data acquisition on PCD side, and a
server program for the package reception and database handling. The investment
is higher than the other solutions but includes all necessary functions to have
a reliable solution without supplementary effort.
The Fboxes
for the data acquisition includes time stamping, buffering, data and site
identification, data level survey with alarming and error reporting. The server
must be installed once and is always able to accept new sites and new data points.
In other words, the data acquisition is transparent from the PCD signals distributed
in several external sites up to the database (e.g
Access file) in the server computer.
In conclusion, this is the
optimal solution for large applications, where data are distributed over
several sites. Maintenance and extension can be expected quite every day. All
efforts have been made in the basic concept to reach an optimal reliability.
Depending on each application the data format, the package transport, the data
base type and many other aspects are adapted to suite the specific need.
Overview
The following table shows
you an overview of these solutions with the various aspects to be considered.
|
DB Logger |
Data |
Web Server |
NG-Dump |
NG-Trace |
NG-Data |
Aspect |
|
No |
No |
Low |
Low |
Medium |
High |
Investment |
|
High |
Medium |
Medium |
Low |
Low |
Medium |
PCD Programming |
|
Yes/High |
Yes/High |
N.A. |
Medium |
Medium |
Medium |
Transfer to SCADA / Realization
work |
|
No |
No |
Yes/Low |
No |
No |
Yes/High |
Web access / Realization
work |
|
Low |
Medium |
High |
High |
High |
High |
Flexibility |
|
Low |
Medium |
N.A. |
Low |
N.A. |
High |
Reliability |
|
Yes |
Yes |
Yes |
No |
Yes |
Yes |
Buffering in PCD
registers or RAM DB |
|
No |
No |
Yes |
Yes |
Yes |
Yes |
Sampling signal included |
|
No |
No |
Yes |
No |
Yes |
No |
Auto recording on change |
|
No |
Yes |
Yes |
Yes |
Yes |
Yes |
Time stamping |
|
No |
No |
Yes |
Limited |
Yes |
Yes |
Data identification |
|
No |
No |
No |
Yes |
No |
Yes |
Site identification |
|
No |
Limited |
No |
N.A. |
No |
Yes |
Buffer diagnostic |
|
No |
Limited |
No |
N.A. |
No |
Yes |
Error reporting |
|
No |
No |
No |
Yes |
Limited |
Yes |
Long time data storage |
|
No |
No |
No |
No |
Yes |
Yes |
Data list view (even
simple view) |
|
No |
No |
Yes |
No |
Yes |
No |
Graphical view (even
simple view) |
|
No |
No |
No |
Yes |
No |
Yes |
Data queuing |
|
No |
No |
No |
No |
No |
Yes |
Value limits and alarming |
|
No |
No |
No |
No |
Yes |
Yes |
Optimized data format |
|
No |
No |
Limited |
Yes |
No |
Yes |
Storage in CSV file |
|
No |
No |
No |
Yes |
Yes |
Yes |
Storage in Excel file |
|
No |
No |
No |
No |
No |
Yes |
Storage in Access
database |
Legend:
Reliability = The ability to recover from communication problem without lost of
data.
Data queuing = The ability to append several data
packages.
N.A. = Not applicable.
If you have further
question, remark or comment about this document, don't hesitate to contact Engiby.
We would be glad to take each opportunity to improve this document.
|
|
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