User Manual

ADC-20/ADC-24 User's Guide 10
Copyright © 2005-2010 Pico Technology Ltd. All rights reserved. adc20.en
4 About the unit
4.1
Introduction
The ADC-20 and ADC-24 High-Resolution Data Loggers offer the ultimate in precise
and accurate readings. Features such as true differential inputs, galvanic isolation
and software-selectable sample rates all contribute to a superior noise-free resolution.
The ADC-20 is equipped with a 20-bit A/D converter, and can maintain a gain error of
0.2%. The four true differential inputs may be configured as eight single-ended
inputs or any combination in between, such as two differential and four single-ended.
The ADC-24 is equipped with a 24-bit A/D converter, and can maintain a gain error of
0.1%. The eight true differential inputs may be configured as 16 single-ended inputs
or any combination in between. Power and connection to a PC or laptop is through a
USB 1.1 or USB 2.0 port. Using the supplied PicoLog software, you can record,
monitor and analyse collected data, even exporting to third-party applications such as
Microsoft Excel.
4.2
Specifications
ADC-20
ADC-24
Input channels
Differential
Single-ended
Configurable up to 4
Configurable up to 8
Configurable up to 8
Configurable up to 16
Conversion time per channel
60 ms, 100 ms, 180 ms, 340 ms, 660 ms
Input voltage ranges
2 ranges
±1250 mV and ±2500 mV
7 ranges
±39 mV to ±2500 mV
Resolution
20 bits
24 bits
Noise-free resolution
See table below
Overvoltage protection
±30 V between any input and common
Common-mode range
Channel to common
Channel to common
Common to earth ground
±1.9 V (±39 mV to ±1250 mV ranges)
±3.0 V (±2500 mV range)
±30 V
Common-mode rejection ratio
Channel to common
Common to earth ground
95 dB (d.c. to 60 Hz)
>125 dB (d.c. to 60 Hz)
Noise rejection
120 dB typical at 50 to 60 Hz
Input impedance
2 MΩ (differential)
1 MΩ (single-ended)
Gain error from source
impedance
0.5 ppm per ohm source impedance
due to input impedance
Gain error
0.2%
0.1%
(0.2% at ±2500 mV)
Offset error
6 µV (±39 mV range)
7 µV (±78 mV range)
9 µV (±156 mV range)
13 µV (±313 mV range)
20 µV (±625 mV range)
36 µV (±1250 mV range)
400 µV (±2500 mV range)
Digital I/O
None
4
Output level, high
Output level, low
Input level, high
Input level, low
> 2.40 V
< 0.40 V
> 2.20 V
< 0.88 V