Sensoray 118 - Manual (Page 4)

Sensoray Model 118 Smart A/D™ Instruction Manual 2 Introduction
2 Introduction
2.1 Functional Description
The Sensoray model 118 Smart A/D™ board provides
eight independent sensor channels that interface process
sensors directly to the VMEbus.
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.
A standard 40-pin header is provided for connecting the
sensor channels to external circuitry. Optional mating
termination boards and cables are available to facilitate
connections to application sensors.
Smart A/D™ features include:
q Embedded processor off-loads the most demanding data
acquisition functions from the host.
q
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.
q
Sensor channels employ fully differential sense inputs to
help eliminate ground loops.
q
All sense inputs are protected from high differential and
common mode voltages.
q 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.
q Sensor excitation signals are electrically separate from the
sense inputs so that high accuracy three-wire or four-wire
circuits may be implemented.
q Automatic cold junction compensation is provided for
thermocouples. The remote compensation sensor—
present on all Smart A/D™ termination boards—connects
to a dedicated measurement channel so that all process
sensor channels remain available for application use.
q
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.
q 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
Figure 1: Model 118 functional block diagram
Excitation
Generator
Digitizer
Excitation
Multiplexer
Sense
Multiplexer
Reference
Standards
S
Y
S
T
E
M
B
U
S
Microcomputer
Bus
Interface
P
R
O
C
E
S
S
S
E
N
S
O
R
S
Optional External
Thermocouple
Reference Sensor