3B Introduction
The
3B Series of Signal Conditioning I/O Subsystems provide a low-cost,
versatile method of transferring analog transducer signals to a data
acquisition, monitoring or control system without the inherent noise,
non-linearity, drift and extraneous voltages. The modules are designed
to directly accept analog signals from Thermocouples, RTD's, ac and
dc Strain Gages, Torque Transducers, Frequency Transducers, LVDTs,
millivolt or process current signals. The modules amplify, isolate,
linearize and convert the transducer output signals to standardized
analog inputs for high-level analog I/0 subsystems. The 3B Series
Subsystem consists of a 19" relay rack with universal mounting
backplane and a family of plug-in (up to 16 per rack) input and output
signal conditioning modules.
Eight- and four-channel backplanes are
also available. Each backplane incorporates screw terminals for sensor
inputs and current outputs and a 26-pin connector for high-level
single-ended voltage outputs to the user's equipment.
The input modules feature complete signal conditioning circuitry
optimized for specific sensors or analog signals and provide two
simultaneous high-level analog outputs: 0 to +10 V (or ±10
V) and 4-20 mA (or 0-20 mA).
Output
modules accept 0 to +10 V (or ±10 V) single-ended signals
and provide an isolated 4-20 mA (or 0-20 mA) process signal. All
modules feature a universal pin-out and may be readily hot-swapped
under full power and interchanged without disrupting field wiring.
The Analog Devices 3B Series Signal Conditioning Subsystem is designed
to easily handle signal conditioning problems in measurement and
control applications. Some typical uses are in microcomputer-based
data acquisition systems, programmable controllers, analog recorders,
dedicated control systems, and any other applications where monitoring
of temperature, pressure, flow and analog signals are required. Since
each input module features two simultaneous outputs, the voltage
output can be used to provide an input to a microprocessor-based
data acquisition or control system while the current output can be
use for analog transmission, operator interface, or an analog backup
system.
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Features and Benefits
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Design Features and User Benefits
Ease
of Use:
Direct sensor interface via screw terminals, standardized high-level
outputs, factory precalibration of each unit and the modular design
make the 3B Series Subsystem extremely easy to use. The subsystem
features rugged packaging for the industrial environment and can
be easily installed and maintained.
High reliability:
To assure high reliability, all field-wired terminations offer
130 V or 220 V rms normal mode protection. Gold plated pin and
socket connectors are used throughout the system to assure connection
reliability. The isolated modules offer protection against high
common mode voltages and are designed to meet the IEEE Standard
for Transient Voltage Protection (ANSI/IEEE C37.90.1-1989).
High
Performance:
The high quality signal conditioning series features ±0.1%
calibration accuracy and chopper-based amplification which assures
low drift (±1 µV/°C) and excellent long term stability.
For thermocouple applications, high accuracy cold junction sensing
is provided in the backplane on each channel. Low-drift sensor
excitation is provided for RTD, strain gauge, and LVDT models.
RTD models and the 3B47 thermocouple
model linearize the input signal to provide an output which is
linear with temperature.
High Noise Rejection:
The 3B Series Subsystem was designed to accurately process low-level
signals in electrically noisy environments by providing excellent
common-mode and normal-mode noise rejection and RFI/EMI immunity.
Figure 1. 3B Series System Functional Block
Diagram
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3B Series Input Modules
Figure 2 shows a functional diagram for the Model 3B37 isolated
thermocouple signal conditioner. The input signal is filtered,
amplified and has cold junction compensation applied before the
isolation barrier. The outputs of the module are isolated from
the input (up to ±1500 V peak) and factory calibrated for
0 to +10V (voltage output) and 4-20 mA (current output), which
correspond to the specified input span.
The input modules are available in several factory-calibrated
input ranges. Each input module includes separate screwdriver-adjustable
zero and span potentiometers for both of the outputs which can
be used for fine calibration within the chosen range. The voltage
and current adjustments are independent and non-interactive, enabling
precise calibration of both outputs.
The current output of each input module has two user-programmable
jumper options. One option enables the user to program the current
output to be proportional to either a 0 to +10 V or a -10 V to
+10 V voltage output. The second option enables the user to set
the current output span to 4-20 mA or 0-20 mA. All modules are
shipped from the factory configured so that the current output
is proportional to the 0-10 V output range and all current outputs
are 4-20 mA.
Figure 2. Model 3B37 Functional Block Diagram
-
Input Module Features
- Wide Variety of Sensor Inputs:
- Thermocouples
- RTD's
- ac and dc Strain Gauges
- Torque Transducers
- Frequency Transducers
- LVDTs
- Dual High Level Outputs
- Voltage: 0 to +10 V or ±10 V
- Current: 4-20 mA/0-20 mA
-
Mix and Match Module Capability
-
High Accuracy: ±0.1%
-
Low Drift: ±1µV/°C
- Reliable Transformer Isolation:
- ±1500 V Peak and CMR = 160 dB
-
Meets ANSI/IEEE Transient Protection
-
Input Protection: 130 V or 220 V rms Continuous
Each input module is a single-channel signal conditioner which
plugs into a socket on the backplane and accepts its signal from
the input screw terminals. All input modules provide input protection,
amplification and filtering of the input signal, accuracy of ±0.1%,
low drift of ±1 µV/°C (low-level input modules),
and feature two high-level analog outputs that are compatible with
most process instrumentation. The isolated input modules also provide ±1500
V peak isolation.
The choice of a specific 3B module depends upon the type of input
signal. Input modules are available to accept millivolt, volt,
process current, thermocouple, RTD, ac and dc strain gage, frequency
and LVDT inputs. The voltage output of each module is available
from the system I/O connector while the current output is available
on the output screw terminals.
Wide Zero Suppression Capability
A wide zero-suppression capability and easy-custom ranging are
available with a unique plug-on ranging card (AC1310). If a special
input range is desired, it can be provided by ordering the externally-programmable
version of the desired module (i.e. 3B32-00) and the plug-on ranging
card, AC1310.This card houses user-supplied resistors which determine
the zero and span of the desired range. RTD modules accept an additional
resistor to establish linearization of the input signal, while
the 3B37 thermocouple module uses an additional resistor to set
the cold junction compensation level. This ranging capability enables
the user to provide zero suppression of up to and beyond 100% of
the input range and provides a very wide range of span modification.
This enables the user to map any portion of the input signal to
the full output span. For example, a user who wants to measure
temperature with a thermocouple in the range of +800°C to +900°C
can use this ranging card for greater system resolution within
that defined 100°C temperature span. This tremendous flexibility
should satisfy virtually any requirement. The resistor values are
determined by equations defined for each module. A software program
(3B-CUSTOM)
is also available to assist in quickly calculating the resistor
values, using only the user-defined input and output requirements.
Special ranges can also be factory configured. Analog Devices
will provide this service when a model 3BXX-CUSTOM is ordered with
the desired range. (The 3B47 linearized thermocouple input module
can not be user ranged with an AC1310 since approximately 15 components
are required for linearization. A factory configured 3B47-CUSTOM
can provide the desired input range.)
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3B Series Output Modules
The 3B39 output module accepts
a high-level analog signal from the system connector and provides
a current output on the output screw terminals. When a +24 V loop
supply is used, loads up to 850 
can
be driven. If desired, +15 V can be used to power the output modules
with a smaller load (up to 400 ).
Each output module features high accuracy of ±0.1%.The
3B39 provides ±1500 V peak common mode voltage isolation
protection.
The transfer function provided by each output module is:
Input - 0 to +10 V or ±10 V
Output - 4 to 20 mA or 0 to 20 mA (Jumper Selectable)
Figure 3 shows a functional diagram of Model 3B39. The input signal
drives a voltage to current converter through the isolation barrier.
Each output module has zero and span potentiometers for fine calibration
of the isolated current output. The output module has two user-programmable
jumper options. One option enables the user to program the current
output to be proportional to either a 0 to + 10 V input or a -
10 V to +10 V input. The second option enables the user to set
the current output span to 4-20 mA or 0-20 mA. All output modules
are shipped from the factory with the current output set proportional
to the 0 to +10 V input and all current outputs are 4-20 mA.
Figure 3. Model 3B39 Functional Block Diagram
| Features
and Benefits
High-Level Voltage Inputs
Isolated Process Current Output
High Accuracy : ±0.1%
Reliable Transformer Isolation: ±1500 V Peak Continuous
Meets ANSI/IEEE Transient Protection
Output Protection : 130 V rms Continuous
Reliable Pin and Socket Connections |
 |
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