Calibration Terminal; Trigger Terminal; Counter Terminal; Accuracy - Measurement Computing USB-1208LS User Manual

USB-1208LS User's Guide

Calibration terminal

The connection (pin 16) is an output you should use only to calibrate the USB-1208LS. Refer to the
CAL
diagrams on page 3-4 for the location of this pin. Calibration of the USB-1208LS is software-controlled via
InstaCal.

Trigger terminal

The connection (pin 18) is an external digital trigger input. You can configure this terminal with
TRIG_IN
software for either trigger high or trigger low.

Counter terminal

Pin 20 ( ) is input to the 32-bit external event. Refer to the
CTR
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-1208LS are offset and gain. Nonlinearity is small in the USB-1208LS,
and is not significant as an error source with respect to offset and gain.
Figure 3-10 shows an ideal, error-free, USB-1208LS transfer function. The typical calibrated accuracy of the
USB-1208LS is range-dependent, as explained in the "Specifications" chapter of this document. We use a
±10 V range here as an example of what you can expect when performing a measurement in this range.
pinout diagrams
3-9
Functional Details
on page 3-4 for the location of
pinout