Sorry, Here my code in plaintext
#While loop - scanning and storing OPC values at scan rate
while (abort == 0):
# ESC pressed?
if msvcrt.kbhit() and ord(msvcrt.getch()) == 27:
abort = 1
break
# Server up
if opc.ping():
if opc['.run_batch'] == True and rec_started == False:
# Setting arrays for variables
bool1 = []
ana1 = []
ana2 = []
ana3 = []
ana4 = []
rec_started = True
if opc['.run_batch'] == True and rec_started == True:
# scan time
time2 = time.time()
dtime = time2 - time1
if dtime > 2 and comm_alarm == False:
dt = datetime.datetime.now()
bool1.append((opc.read('.watchdog')[0],opc.read('.watchdog')[1],dt))
ana1.append((opc.read('.analog2')[0],opc.read('.analog2')[1],dt))
time1 = time2
else:
# scan time
time2 = time.time()
dtime = time2 - time1
if dtime > 2:
print "ERROR: OPC Server is down”
Il giorno 19 febbraio 2016 @ 02:18:05, Alan Gauld (alan.ga...@btinternet.com)
ha scritto:
> Let's say I can have 30-40 variables (so 30-40 append instructions at every
> cycle, with same scan rate).
Its not clear what the scan rate actually is.
How many scans per second?
yes scan per second. For example a new fetch every 2 second, so a new append to
array every 5 second
> shall run for 2 hours and gather let's say 2000 elements in 40 arrays,
> could this be a problem in term of computation?
Yes it could, but it depends on what size the data is.
You need to do some basic math to calculate it out.
40 * 2000 = 80k items. If they are integers then its
4 bytes per item so 320Kbytes. Not too bad. If they
are 100 character strings then its into MB but on a
modern PC still not too bad. But if it's intended to
run in an embedded controller with only 1M of RAM
it might be a big issue.
Pc for sure, I think with 8GB RAM. I’ll do some detailed calculations about
that.
> Second question is I want the arguments in the opc.read command not to be
> hard coded but coming from a configuration files.
OK. You might want to think about what that file
format would look like.
I’d like to have an xml file or csv file to parse (another topic I wanna learn)
and in this file I have a table defining my variables with a name and another
field for description
> You see the names of my arrays? bool1, ana1, ana2, etc... Is it possible to
> derive number and names of these variables from an external files.
It is but its usually a bad idea.
Better is to use a dictionary with your "variables"
as keys and your arrays as values. So your append
looks like
data = dict()
keyName = readFromFile()
value = readFromFile()
data[keyName].append(value)
Ok so I will look more into dictionaries, it is like hash tables?
> Let's say in this configuration file I can say I have to read 10 arrays or
> 20 arrays and then my program adjust the while cycle consequently.
Yes that's doable.
> Maybe an array of array where the second dimension is coming from the
> config file.
I'd use the dictionary approach rather than arrays of arrays.
(Which are probably lists of lists in Python.)
Thanks!
Marco
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