Sensoray 618 - Manual (Page 4)

Sensoray Model 618/619 Smart A/D 2 Introduction
2 Introduction
2.1 Functional Description
Sensoray models 618 and 619 Smart A/D boards provide
eight (model 618) or sixteen (model 619) independent
sensor channels that interface process sensors directly to
the PCI bus.
An onboard microcomputer continuously scans the
sensor channels. As each channel is scanned, the sensor
is excited, digitized, linearized, converted to engineering
units appropriate for the sensor type, and stored in
onboard memory. The freshest sensor data from all
channels are always available for instant access.
Standard 100 mil, 40-pin headers are provided for
connecting the sensor channels to external circuitry.
Optional mating termination boards are available to
facilitate connections to application sensors.
Smart A/D features include:
• Embedded processor off-loads the most demanding
data acquisition functions from the host.
• Each sensor channel may be independently configured,
via software, to accept thermocouples, RTD’s, strain
gages, thermistors, resistors, 4-to-20 mA current loops,
or DC voltage inputs.
• Sensor channels employ fully differential sense inputs
to help eliminate ground loops.
• All sense inputs are protected from high differential
and common mode voltages.
• Pulsed excitation is provided for passive sensors, such
as thermistors, resistors, RTD’s, and strain gages.
Pulsed excitation minimizes sensor self-heating effects
and helps to reduce system power consumption.
• Sensor excitation signals are electrically separate from
the sense inputs so that high accuracy three-wire or
four-wire circuits may be implemented.
• Automatic cold junction compensation is provided for
thermocouples. The remote compensation sensor—
present on all Smart A/D termination boards—employs
a dedicated measurement channel so that all process
sensor channels remain available for application use.
• Programmable alarm limits for each channel. A
hardware Alarm status flag provides instant access to
limit violation detection without cumbersome polling
and evaluation of sensor data for limit violation
detection.
• Fully electronic calibration—no trimpots to adjust.
Highly stable internal standards provide excellent
measurement accuracy without the need for frequent
calibrations.
2.2 Block Diagram
Excitation
Generator
Digitizer
Excitation
Multiplexer
Sense
Multiplexer
Reference
Standards
S
Y
S
T
E
M
B
U
S
Microcomputer
Bus
Interface
Power
Supplies
P
R
O
C
E
S
S
S
E
N
S
O
R
S
Optional External
Thermocouple
Reference Sensor