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750 Interface (USB)
Model No. CI-7599
18
®
Digital Input/Output Channels
When a digital sensor plugged into one or more of the 750 interface,
the interface may perform several different tasks, with the task
dependent on the type of sensor connected. It may time the interval
between external events (i.e. a photogate), count external events (i.e. a
nuclear sensor), or it may both trigger an external event and perform a
timing function ( i.e. Motion Sensor). When you choose a particular
digital sensor in DataStudio, information is transmitted to the 750
inteface, and the microprocessor within the interface knows what to do
and when, and on which channel. The timing function is carried out
within specialized digital devices within the 750 interface, called Field
Programmable Gate Arrays. These devices are programmed to
perform many digial functions and perform them at very high speeds.
Sampling Rate
The maximum samples rate depends on the channels the user selects
for measurement. For higher sample rates, the interface samples a
block of 2000 bytes and then transfers the block. Once transfer of
bytes to the host begins, the interface starts sampling a new block.
This is called
burst mode
, since there is a small time interval when data
is not being sampled. The main use of this mode is for the virtual
oscilloscope. Table 1 shows the sampling constraints while using a
fast computer to record the data.
Table 1: Sample Rate Constraints
Sample
Rate
No. of Channels
Comment
250 KHz
1 analog
Burst mode
100 KHz
3 analog
Burst mode
50 KHz
5 analog
Burst mode
20 KHz
1 or 5 analog
Continuous* (burst)
10 KHz
1 1 digital or
5 analog
Continuous* (Burst)
< 100 Hz
5 analog
Continous 8x oversample
(improved accuracy at < 100
Hz)