AD 6B21

Isolated, Field Configurable Analog Input
Module accepts commands from the host computer and
converts it into an isolated process current suitable for
interfacing with valves and actuators.
Complete microcomputer-based data acquisition systems.
Output range can be selected to either a 0 to 20 mA or 4 mA
to 20 mA process current.
RTD and thermocouple, and a wide variety of input ranges. This
reduces the number of different modules that need to be used
in a given application and carried in inventory.
Process Monitoring & Control
Test Stand Automation
Machine Monitoring
Material Testing
Remote Energy Mangement
Laboratory Data Acquisition
Figure 1. 6B21 Functional Block Diagram
The 6B Series delivers sensor-to-host signal-conditioning for
remote applications. Software-configurable for a wide variety of
sensor types, including: analog input, analog output, and digital
I/O, the 6B Series is intended for remote data acquisition,
machine monitoring, remote energy management and process
monitoring and control applications.
Designed for industrial applications, the 6B Series modules
incorporate transformer-based isolation with surface-mount
manufacturing technology – providing increased reliability at
low cost. The compact, rugged 6B Series analog modules can be
mixed and matched on a 16-channel backplane for high density,
remote process monitoring and control.
Including transformer-based isolation, ranging, linearization,
A/d conversion and RS-232C/RS-485 serial communication for
up to 256 channels per serial port, the 6B Series modules and
boards are a complete, low-cost interface between computers
and analog signals.
Communications between backplanes, modules and host is in
ASCII over an RS-232C link or RS-485 bi-directional serial bus.
Circuitry to convert RS-232C to RS485 is built into the 6B
backplane. Baud rates are software programmable, with speeds
up to 19.2 K Baud.
All 6B Series input/output modules are fully encapsulated and
identical in pin-out and size, facilitating their ability to be mixed
and matched with all other 6B Series modules on the same
backplane. The 6B Series is fully rated over the industrial
temperature range of -25oC to +85oC.
The 6B Series digital subsystem communication is compatible
with the overall 6B Series communication protocol. Each digital
I/O board can be configured for its address, baud rate and
checksum status. Connection to the 16 and 24-channel solid
state relay backplanes is by a 50-conductor ribbon cable. This
enables interfacing with input and outputs from 4 V to 240 V.
Power control modules are also available that can switch up to
3A and come with a variety of ratings for low voltage DC up to
280 VAC.
Each 6B Series module and board is a complete
microcontroller-based process monitoring and control system,
with all calibration, address and linearizing parameters stored in
non-volatile memory. Being microcontroller-based, 6b Series
modules can be configured for various sensor types, including
Rev. 0
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However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.326.8703
© 2004 Analog Devices, Inc. All rights reserved.
through an RS-485 port to exchange command and status
information. An included EEPROM stores calibration constants
as well as configuration information. The microcontroller also
controls the output DAC through an optically-isolated serial
interface. The D/A converter drives the current loop through a
protective V/I (voltage-to-current) converter. The output
monitor is a V/F converter whose frequency is proportional to
the loop current. This variable signal frequency is fed back to
the microcontroller through an optical isolator. The
microcontroller then scales the frequency signal and returns the
current read-back data to the host computer. A DC/DC
converter generates 25 VDC from the +5 VDC power supply to
power the current loop and output circuitry.
The 6B21 is a single-channel signal-conditioning module which
provides a digitally-controlled isolated current loop output to a
resolution of 12 bits. The output range can be selected to either
a 0 to 20 mA or 4 mA to 20 mA process current. It is electrically
and mechanically compatible with the 6B Series input modules
and backplanes. The 6B21 takes a command from the host
computer and converts it into an isolated process current
suitable for interfacing with valves and actuators. The 6B21
offers a normal mode output protection of 240 V rms as well as
1500 V rms CMV isolation. In addition the actual current
flowing in the current loop is read back by an on-board isolated
V/F (voltage-to-frequency) converter.
The 6B21 can be software-configured for address, output range,
baud rate, data format, checksum status, slew rate, and start-up
value. All programmable parameters are stored in the
nonvolatile memory of the module.
An on-board microcontroller communicates with the host
Figure 2
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Model 6B21
Range Description
(Software Configurable)
0 mA to 20 mA
±0.02 % FSR
±0.05 % FSR
4 mA to 20 mA
±0.02 % FSR
±0.05 %FSR
6B21 Specifications
(typical @ +25°C and Vs = +5 V dc)
Model 6B21
Output, Software Selectable
Current, Operating Ranges
0 mA to 20 mA or 4 mA to 20 mA
Current, Over-range
+2 mA ±200 µA
Load Resistance
0 to 750 Ω
Baud Rates, Software selectable
300K, 600K, 1.2K, 2.4K. 9.6K, 19.2K
Output Current
Initial Accuracy
Output Offset
±5 µA (±15 µA maximum)
±0.02% Full Scale Range
(±0.05%, max.)
Accuracy vs. Temperature
Output Offset Current
±1 µA°C
±50 ppm/°C
±0.02% Full Scale Range
±0.02% Full Scale Range
Output Noise, 0.1 Hz to 100 Hz Bandwidth
1 µA peak-to-peak
Bandwidth, -3 dB
3 Hz
Conversion Rate
100 samples/second
Setting Time
1 ms to ±0.1% Full Scale Range
Output Slew Rate
Software Selectable (11 Binary Ranges)
0.125 mA/sec to 128 mA/sec
Common-Mode Voltage (CMV)
Output-to-Input and Power
1500 V rms continuous
Common Mode Rejection (CMR)
Output-to-Input and Power @60 Hz
108 dB
Output Protection
240 V rms, continuous
Output Transient Protection
ANSI/IEEE C37.90.1-1989
Rev. 0 | Page 3 of 8
Output Readback
Initial Accuracy @ +25°C
Output Offset Current
±100 µA
±0.5% Full Scale Range
Accuracy vs Temperature
Output Offset Current
±5 µA/°C
±200 ppm/°C
±0.5% Full Scale Range
±0.5% Full Scale Range
Power Supply
Voltage, Operating
+5 V dc ±5%
Voltage, maximum safe limit
+6.5 V dc
+250 mA
Mechanical Dimensions
2.3" x 3.1" x 0.79"
(58.4 mm x 78.7 mm x 19.1 mm)
Temperature Range
Rated Performance
-25°C to +85°C
-25°C to +85°C
-40°C to +85°C
Relative Humidity
0 to 95% @ +60°C, non-condensing
Specifications subject to change without notice.
Rev. 0 | Page 4 of 8
Figure 3 . Model 6B Series Module, with pin-out assignments.
Table 1. Pin Function Descriptions—
Pin No.
Figure 4 6B21Input Field Connections
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human
body and test equipment and can discharge without detection. Although this product features proprietary ESD
protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges.
Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
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Figure 5. Outline Dimensions
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© 2004 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective companies.
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