Chapter 1: Functional Description
Manual Number: 00650-014-4
Page 1-1
Chapter 1:
Functional Description
The AD12-8 is a multifunction, moderate-speed analog-to-digital converter card with counter/tim-
ers and digital I/O ports. This card may be used in any PC compatible computer. The card is seven
inches long and requires one slot in the computer. All external connections are made through a
standard 37-pin D-type connector at the rear of the computer. The following paragraphs describe
the functions provided by the AD12-8 card.
Analog Inputs
The card accepts eight single-ended analog input channels. The full scale input for all channels is
jumper selectable, either ±10V (0.00488V resolution), or ±5V (0.00244V resolution), or unipolar
0 to 10V (0.00244V resolution). Inputs are single-ended with a common ground and can withstand
overvoltages up to ±30 volts and brief transients of several hundred volts. When power is off, the
inputs are open-circuited providing fail-safe operation. The analog-to-digital converter (A/D) is a
12-bit successive-approximation type with a sample and hold input. Conversion time is typically
25
m
S (35
m
S maximum) and, depending on the speed of the software and computer platform, through-
puts of up to 40,000 conversions per second are attainable.
Input System Expansion
The AD12-8 card may be used alone or it can support up to eight AT16-P or LVDT8-P analog input
expansion cards. An 8-bit standard LSTTL logic output from the AD12-8 is used to control the
AT16-P (These outputs are separate from the discrete I/O lines discussed later.). Four bits are used
to select one of 16 analog input channels at the AT16-P. Three bits are used to select one of eight
gains for the selected input channel. The remaining bit is a digital output (sink current 8mA, source
current 0.4mA). When interfacing to the LVDT8-P, three bits are used to select one of eight
LVDT8-P inputs. Since the eight-input multiplexer on the AD12-8 card is software addressable, an
input expansion card may be connected to each input, for a maximum of 128 channels in the
system. If more than 128 analog inputs are required, a second AD12-8 with companion input
expansion cards can be used.
Discrete Digital I/O
The AD12-8 card provides eight bits of individually jumper-programmed digital input and/or out-
put. The outputs can sink 24mA or source 2.6mA. For ease of use, we suggest that you use the
Screw Terminal Accessory Board, model UTB to make external connections.
Reference Voltage Output
A pre10.0V (±0.1V) reference voltage output is derived from the A/D converter reference.
The reference voltage is buffered and will source up to 220mA, which is sufficient for exciting
several strain gage sensors, load cells, or other transducers.
