Introduction 2, Functional description, Block diagram – Sensoray 417 User Manual
Page 4
Chapter
2
Introduction
2
Functional Description
The Model 417 circuit board interfaces 32 process sensors directly to the ISAbus. Each of its 32
sensor channels may be independently configured, via software, to accept thermocouples, 4-to-20
mA current loops, or DC voltage. Sensor channels utilize true differential inputs to allow for wide
common mode variation.
Cold junction compensation and open-sensor detection is provided for thermocouples, and all
inputs are protected from high differential and common mode voltages.
Under firmware control, an onboard microprocessor continuously scans the 32 channels. As each
channel is scanned, the sensor signal is digitized, linearized, and converted to engineering units as
appropriate for the declared sensor type. Each channel’s most recently acquired data may be
quickly accessed by the ISAbus host.
Alarm limits are programmable for each channel. A status flag is set when limit violations occur,
enabling the host to quickly detect alarm conditions.
Communication with the ISAbus host takes place over two contiguous ports which may be
mapped anywhere in the system I/O address space. Local communication and scanning tasks
execute in a high-performance multitasking environment, optimizing both throughput and host
communication latency.
Block Diagram
DIGITIZER
µ
COMPUTER
COMMAND
REGISTER
DATA
REGISTER
STATUS
REGISTER
SENSOR
SIGNALS
THERMOCOUPLE
REFERENCE
REFERENCE
STANDARDS
IS
A
B
U
S
I
N
T
E
R
F
A
C
E
D
IF
F
E
R
E
N
T
IA
L
M
U
X
IS
A
B
U
S