SCM9B
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107
Isolated Intelligent Signal Conditioning Products
SCM9B
SCM9B-D100 Series
DIN Rail Mount Sensor-to-Computer Modules
Features
Complete Sensor to RS-485 Interface
500Vrms Analog Input Isolation
15 Bit Measurement Resolution
Continuous Self-Calibration; No Adjustments
of Any Kind
Programmable Digital Filter
Requires +5VDC Supply
Transient Suppression on RS-485
Communications Lines
Screw Terminal Plug Connectors Supplied
CE Compliant
▲
Description
The SCM9B-D100 Sensor to Computer Modules are a family of data acquisition
modules that convert analog input signals to digital data and transmit via RS-485
to a controller which may be a computer or other processor-based equipment.
The modules can measure temperature, pressure, voltage, current, digital input
or digital output signals. The modules provide direct connection to a wide variety
of sensors and perform all signal conditioning, scaling, linearization and
conversion to either linearized ASCII data values or Modbus RTU data values.
Features such as address, baud rate, parity, echo, etc., are selectable using
simple commands over the RS-485 port. The selections are stored in nonvolatile
EEPROM which maintains data even after power is removed.
Data is acquired on a per channel basis so you only buy as many channels
as you need. The modules can be mixed and matched to fit your application.
They can be placed remote from the host and from each other. You can string
up to 247 modules on a twisted pair of wires by using RS-485 with repeaters.
All modules are supplied with screw terminal plug connectors. The connectors
allow system expansion, reconfiguration or repair without disturbing field wiring.
Utility software is available from Dataforth to make the D100 easier to learn and
use. The software is provided at no charge on request with a purchase order
and is not copy protected.
Theory Of Operation
Each Dataforth module is a complete single-channel data acquisition system.
Each unit contains analog signal conditioning circuits optimized for a specific
input type. Sensor signals are converted to digital data with a micro
processor-controlled integrating A/D converter. Offset and gain errors in the
analog circuitry are continuously monitored and corrected using microprocessor
techniques. The D100 converts the digital signal data and stores the resultant
data in a memory buffer. The modules continuously convert data at the rate of
8 conversions per second and store the latest result in the buffer.
Host processors may request data by sending a query to the module. The D100
will instantly respond by communicating the memory buffer data back to the host
processor. Up to 247 modules may be linked to a single RS-485 port. Each
module on a serial line is identified by a unique user-programmable address.
This addressing technique allows modules to be interrogated in any order.
Digital Inputs/Outputs
D170 digital input/output modules contain open-collector transistor switches that
may be controlled by the host processors. These switches may be used to
control solid-state relays which in turn may control heaters, pumps and other
power equipment. The digital inputs may be read by the host processor and
used to sense the state of remote digital signals. They are ideal for sensing the
state of limit or safety switches.
Digital Filter
The D100 analog input modules include two unique programmable single pole
digital filters. The filter is used to smooth analog data in noisy environments.
Separate time constants may be specified for small and large signal changes.
Typically a large time constant is specified for small signal changes to filter out
noise and provide stable output readings. A smaller time constant may be chosen
for large signal changes to provide fast response to such changes.
Command Set
The D100 series uses the Modbus RTU or the Dataforth ASCII protocol for
communication.
The Modbus RTU binary protocol uses a master-slave technique, in which only
the master device can initiate transactions. The slave devices respond by
supplying the requested data to the master or by taking the action requested
in the query. The master can address any slave device. The returned
messages are considered response messages. The supported master codes
are:
Modbus RTU Functions and Descriptions
01 Read Coil Status (Digital Inputs)
04 Read Input Register (Analog Inputs)
05 Force Single Coil (One Digital Input)
06 Preset Single Register (Dataforth/RTU Protocol)
15 Force Multiple Coils (Multiple Digital Output)
The Dataforth ASCII protocol is a command and response protocol using ASCII
characters for easy troubleshooting and interpretation of data values.
Figure 1: SCM9B-D100 Block Diagram
(11 Seiten)
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