Vernier LabPro - Manual (Page 7)

Revision Date: 08/02/02
LabPro Technical Manual 7
In order to clear all settings, send a reset, 0 command. This command clears data collection RAM, channel
assignments and data collection modes that are currently assigned in LabPro. This is a good first step to
put LabPro into a known state before configuring the channels. However, this is not to say that a reset
should always be sent to LabPro. In fact, since reset clears previous data, it is important to send reset only
when you are sure the user is done with the current configuration and data.
Example:
7 //Ask for status from LabPro
Get response //Evaluate response
0 //Reset LabPro to prepare for channel activation etc.
Channel Activation
In order to collect data from LabPro, the program must activate one or more channels. The channel setup
commands (Command 1 and Command 12) provide a means by which the program configures LabPro to
collect data from certain ports. This part of the program is where the channels are activated, calibration
equations are loaded and post-processing options are set. Channel activation tells LabPro which ports are
active and how to collect data from that port. Calibration equations are used to convert the raw voltage
reading to units specific to the sensor connected to the port. Post processing options further process the
data prior to returning the information to the host.
Data Collection Modes
Once LabPro has been initialized and the channels have been activated, the data collection details must be
programmed. Data may be collected and returned in several different formats depending on the host.
However, there are two basic modes of data collection, real time (RT) and non-real time (NRT). These
terms are a little misleading in that data is always collected in real time. The modes differ in how data is
stored in and retrieved from LabPro.
In RT data collection, data is collected at regular intervals and available to the host on a point by point
basis. Data collection begins after LabPro has processed the command. Only the most recent point is
stored in LabPro. If the program does not ask for the data often enough, data could be lost. In this mode,
data collection is performed as part of the main processing loop. Therefore, other tasks and processing will
determine when an opportunity for data collection occurs. LabPro attempts to take data as close as
possible to the programmed time interval. The accurate time between samples is reported back for each
data point. This is usually within 100 ms of the requested time. LabPro continues taking data until the host
stops data collection or resets the unit. This mode is useful for relatively slow time-based data collection
where an unlimited number of data points is necessary; such as a scrolling strip chart recorder.
In NRT data collection, data is collected at regular intervals. Data collection is interrupt-driven to achieve
accurate sample periods. Using a wide variety of definable triggers, the program may control when data
collection begins. LabPro stores the data in internal RAM until the requested number of data points have
been collected. The unit will return the list of data only after receiving a ‘get request’ from the host. If the
host sends the “get request” before data collection is complete, LabPro will begin data transmission after
the last point is sampled. It is possible to monitor the data as it is being collected by using Command 8.
This feature could be used to give the user a real-time view of data being collected in a NRT mode. Due to
its flexibility, this is the most commonly used mode. A special case of the NRT mode is FastMode
sampling. It is designed for use when a single channel must be sampled very quickly. This mode is used
primarily when sampling sound with a microphone, or to approximate an oscilloscope. In general,
FastMode is identical to non-realtime sampling with the following exceptions:
•
The sampling is limited to a single analog channel.
•
The selected channel must not be in operation mode 5, 6, or 7.