The converter is comprised of a 4th-order, delta-sigma (Δ∑) analog-to-digital (A/D) converter modulator followed by a programmable digital filter. A flexible input multiplexer handles differential or single-ended signals; the programmable filter allows the user to optimize between a resolution of up to 23 bits noise-free. Examples of scan sequences, with various channel resolutions and calibration arrangements, appear in Table 5-1 on page 5-2.
4.7 Input Ranges
You can individually select the input range for each channel. For example, one channel could be used for volts and another for temperature. Omega’s OM- DAQ-USB-2401 automatically assigns the appropriate units depending on two factors:
•The selected range and
•Measurement unit preferences
Measurement unit preferences can be modified from the Omega DAQ Central ‘Channels’ tag of the ‘Configuration’ window. Chapter 4 provides more detailed information.
NOTE:
The maximum voltage input range (full scale) is –10 to +10 Vdc. The lowest programmable voltage input range is -30mV to +30 mV. A complete list of the OM-DAQ-USB-2401’s programmable ranges appears on page 8-1.
Each analog input channel has the following user-specified measurement parameters:
•Signal type: volts, or thermocouple type J, K, T, E, R, S, B, or N
•Full scale voltage: from -10 to + 10 Vdc; with programmable ranges as indicated on page 8-1.
•Resolution/sample period: from 22.5 bit RMS at 0.153 samples/sec, to 17 bit RMS at 50 samples/sec or greater
NOTE:
These rates were obtained with a 16-channel scan.
4.8 Analog Input Configuration
The OM-DAQ-USB-2401 includes 16 analog signal inputs which may be used as 16 single-ended inputs, 8 differential inputs, or as a combination of single-ended and differential inputs with up to 16 connections.
Single-ended inputs are used with signals that share the same common low (COM), such as multiple batteries which have their negative sides connected in common. Differential inputs are required when signals do not share the same common low, such as in the typical use of thermocouples.
