UMDAS 0802DA User's Guide

Functional Details

+2.5VREF terminal

The +2.5VREF connection (pin 16) is an output terminal that supplies 2.5 volts. The images below show the +2.5VREF pin configured as the voltage source for channel 0.

Single-ended measurement

Differential measurement

SYNC terminal

The SYNC connection (pin 19) is a bidirectional I/O signal. You can use it for two purposes:

!Configure as an external clock input to externally source the A/D conversions. The SYNC terminal supports TTL-level input signals of up to 48 kHz.

!Configure as an output to synchronize with a second UMDAS 0802DA and acquire data from 16 channels. For information on synchronizing multiple units, refer to page 3-11.

Ground terminals

The four analog ground (AGND) connections provide a common ground for all UMDAS 0802DA input channels. Four ground (GND) connections provide a common ground for the DIO, TRIG_IN, CTR, SYNC and PC +5V connections. Refer to the "Main connector and pin out" diagrams on page 3-3for the location of these pins.

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 "14-bits" or "1 part in 16383" 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 UMDAS 0802DA are offset and gain. Nonlinearity is small in the UMDAS 0802DA, and is not significant as an error source with respect to offset and gain.

Figure 3-10shows an example of an ideal, error-free, UMDAS 0802DA transfer function. The typical calibrated accuracy of the UMDAS 0802DA 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.

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