Vernier LabPro - Manual (Page 14)

Revision Date: 08/02/02
LabPro Technical Manual 14
send a Command 6:
6,0
This will terminate data collection while keeping intact the data buffer and the channel configuration.
Keeping Power on During Analog Data Collection
LabPro tries to minimize power consumption by turning power off to sensors when data is not being
collected. There are some subtle issues involved with reading signals from sensors such as Vernier pH,
Conductivity, Ion Selective Electrodes, Dissolved Oxygen, CO
2
, and Flow Rate. These sensors all require
power to be supplied for some time to stabilize before readings are accurate. The way to solve this
problem is to send a Command 102 as shown the sample below. This command can be sent right after the
channel is set up. Command 102 controls how many seconds prior to sampling that power is applied to the
sensor. The –1 operation tells LabPro to keep power applied to the sensor at all times.
102,-1
Note that if you do this battery life will be reduced.
Digital Data Collection
Digital data collection using photogates, radiation monitors, and rotary motion probes are handled very
differently from analog data. In all cases, Command 12 is also used for setup and to retrieve the data.
Experiments can be performed using analog, sonic and digital channels simultaneously, but will require
additional steps during their set up and data recovery phases.
Important Note: Currently, at least one analog channel must be active in order to collect digital data. The
operating system does not collect data unless this is done. This is a known limitation and it may be
eliminated in future operating system.
Photogate Timing
Photogates operate a little differently than the analog channel since the event occurrences are not
predetermined in time. There are many different timing modes as well. In order to allow the greatest
flexibility, the operating system commands are implemented in a rather generic way. It is up to the
program to process the data as needed to report the desired timing.
Photogate operation is also unique in that the same command (12) is used to setup data collection as well
as request gathered data. Use Command 12 prior to data collection to set up the timing modes. Use
Command 12 during and/or after data collection to retrieve the requested data.
In general, you will need to follow this sequence:
Set up an analog channel (even if you will not use the data collected)
Set up timing mode using Command 12
Start data collection using Command 3
Data collection terminates either manually or automatically (time interval is up)
Retrieve data using Command 12 followed by a “get”
Process data for desired timing information
A word about Command 3 setup. In most of the timing modes (except counter mode) the sampling period
is not a concern unless analog data is really needed. In most cases, this will be set for an arbitrarily long
experiment that is terminated by the user.
LabPro handles multiple digital inputs as separate measurements. The user is allowed to set up a wide
variety of combinations to get the timing they desire. However, it is up to the host program to use the