Vernier LabPro - Manual (Page 12)

Revision Date: 08/02/02
LabPro Technical Manual 12
Many of these features may not be needed and left in their default state or set to zero. Here are the
commonly used parameters:
samptime = the time between samples (in seconds). The range is 0.00002 to 16000 seconds.
numsamp = the number of readings to be made. This can be any integer from 1 to 12,000. (Numsamp
= -1 puts LabPro into RT data collection mode as explained below.)
trigtype = this specifies if the program should wait for a triggering event before starting the actual
data collection. “0” instructs LabPro to begin data collection immediately without waiting for a
trigger. “1” means wait for the Start/Stop button on Labpro to be pressed. Other numbers can be used
to specify triggering on a certain signal level. The default is 1, which you usually do not want, so you
should almost always have to put a zero here.
The last two commands of our sample program are used to retrieve data from LabPro.
Get Analog Data
Get Time Data
As the first four commands of our sample program are executed, LabPro will go about its business of
collecting the data. The program should at some point send a command to LabPro requesting the data. The
details of this are different depending on the computer or calculator being used. Each command will get a
complete list of data from LabPro. The analog sensor readings will be retrieved first and then the times. If
we had set rectime to 0 in Command 3, then we would not have had the times recorded, and we would
have used only one retrieve command.
Analog RT Data Collection
The discussion above is about non-realtime data collection. That is, it assumes that you want to have a
certain number of readings taken at specified intervals for later use by the host (e.g., making a graph).
There is another variation of data collection that is sometimes used. We call this RealTime (RT) data
collection. In this type of program, LabPro takes one reading, the computer retrieves the reading (and
usually does something with it, such as put a point on a graph), and then the program loops and repeats.
Here is pseudo-code for a second sample program, similar to the first, but with RT data collection:
0
1,1,14,0,0,1
4,1,1,1, 8.729,8.271
3,1,-1,0
Label A
Get value of I
Display I
Goto A
This program is the same as the previous sample through the first three lines. After that, the data collection
portion is very different. Here is what is going on:
3,1,-1,0 Note the Command 3 now has a -1 for the number of samples. This will
tell LabPro to take one reading and continue on.
Label A This is just a label, so the program can loop back here.
Get value of I Get the one reading and store it in the variable I.
Display I Display this reading.
Goto A Loop back to Label A and repeat.
Note that in most real programs you need to provide a graceful way of breaking out of this loop.