5.4 Single-Ended / Differential A/D Channels

The input channels on DMM-32DX-AT can be configured as 32 single-ended, 16 differential, or 16 single-ended + 8 differential. Four different configurations are possible as described below.

A single-ended input is a single-wire input (plus ground) that is measured with reference to the board’s analog ground. In order for the measurement to be accurate, the board’s ground must be at the same potential as the source signal’s ground. Usually this is accomplished by connecting the two grounds together at some point, for example by connecting to one of the analog ground pins on the I/O header J3.

A differential input is a two-wire input (plus ground) that is measured by subtracting the low input from the high input. This type of connection offers two advantages: It allows for greater noise immunity, because the noise, which is present in equal amounts and equal phase on both the high and low inputs, is subtracted out when the low input is subtracted from the high input; and it allows for the signal to float away from ground. Normally the ground of the signal source is still connected to the ground on the A/D board in order to keep the signal from straying out of the common mode range of the A/D board’s input circuitry.

To configure the input channels, set jumpers in jumper block J5 according to the table below. For safety reasons, do not modify J5 while the board is powered on. The corresponding channel numbering on the I/O header J3 is shown in drawings A-D (only the first 17 rows are shown; the remaining rows are the same as shown on page 7).

A/D Channel Mode Configuration