Ground Terminals; External Trigger Terminal; Sync Terminal; Counter Terminal - Measurement Computing USB-1208FS User Manual

USB-1208FS User's Guide

Ground terminals

The four analog ground (
Four ground (GND) connections provide a common ground for the
connections. Refer to the

External trigger terminal

The connection (pin 18) can be configured for either rising or falling edge. Refer to the
TRIG_IN
diagrams on page 15 for the location of the

SYNC terminal

The connection (pin 19) is a bidirectional I/O signal. You can use it for two purposes:
SYNC

Configure as an external clock input to externally source the A/D conversions. The SYNC terminal
supports TTL-level input signals of up to 50 kHz.

Configure as an output to synchronize with a second USB unit and acquire data from 16 channels.
Refer to the pinout diagrams
multiple units, refer to page 23.

Counter terminal

The connection (pin 20) is input to the 32-bit external event. Refer to the
CTR
the location of this pin. The internal counter increments when the TTL levels transition from low to high. The
counter can count frequencies of up to 1 MHz.

Accuracy

The overall accuracy of any instrument is limited by the error components within the system. Quite often,
resolution is incorrectly used to quantify the performance of a measurement product. While "12-bits" or "1 part
in 4096" does indicate what can be resolved, it provides little insight into the quality of an absolute
measurement. Accuracy specifications describe the actual results that can be realized with a measurement
device.
There are three types of errors which affect the accuracy of a measurement system:

offset

gain

nonlinearity.
The primary error sources in the USB-1208FS are offset and gain. Nonlinearity is small in the USB-1208FS,
and is not significant as an error source with respect to offset and gain.
Figure 11 shows an ideal, error-free, USB-1208FS transfer function. The typical calibrated accuracy of the
USB-1208FS is range-dependent, as explained in the "Specifications" chapter on page 25. We use a ±10 V
range here as an example of what you can expect when performing a measurement in this range.
) connections provide a common ground for all USB-1208FS input channels.
AGND
pinout diagrams on page 15 for the location of the
TRIG_IN
on page 15 for the location of this pin. For more information on synchronizing
,
DIO TRIG_IN
AGND
terminal pin.
pinout diagrams
20
Functional Details
, , and
CTR SYNC PC +5V
and terminal pins.
GND
pinout
on page 15 for