3B Series Overview


3B SeriesThe 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).

an0026_siloOutput 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.

Features and Benefits

  • Isolated Input Signal Conditioners for a Wide Variety of Sensors, Thermocouples, RTD's, Frequency Transducers, and LVDTs, Millivolt, Volt and milliamp inputs
  • Non-isolated Input Signal Conditioners for ac and dc Strain, Torque Transducers, and Load Cells
  • Isolated Current Output Modules, 4-20 mA/0-20 mA
  • Simultaneous Voltage and Current Outputs
  • Provides 0 to +10 V or ±10 V, 4-20 mA/0-20 mA Outputs
  • Reliable Transformer-based Isolation
  • Specifications Rated Over the -25°C to +85°C Operating Temperature Range
  • Accuracy for all Module Types is ±0.1%
  • Chopper-Stabilized Amplification Assures Low Drift (±1 µV/°C) and Excellent Long-Term Stability
  • User-Configurability with the AC1310 Ranging Card

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.

 3B Series Functional Block Diagram
Figure 1. 3B Series System Functional Block Diagram

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.

Model 3B37 Functional Block Diagram
 Figure 2. Model 3B37 Functional Block Diagram

Input Module Features

  • Wide Variety of Sensor Inputs:
    ac and dc Strain Gauges
    Torque Transducers
    Frequency Transducers
  • 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

an0036A 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.)

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 Ω can be driven. If desired, +15 V can be used to power the output modules with a smaller load (up to 400 Ω). 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.

 Model 3B39 Functional Block Diagram
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