ANALOG DEVICES 3B20 Service Manual

AC Strain Gage, Torque Transducer Input

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FEATURES

Interfaces, amplifies, & filters signals from 4-arm AC bridge
transducer signals ranging between 1.5mV rms & 150mV
rms.

Module provides an AC excitation voltage of 2V rms to 10V
rms at frequencies between 1kHz & 10kHz..

Module provides simultaneous precision voltage and
current outputs.

Module circuitry can withstand 130v rms at its current
output terminals without damage.

All 3B20 series modules are mix-and-match and Hot
Swappable

APPLICATIONS

Industrial signal conditioning
Industrial signal isolation
Industrial signal filtering

PRODUCT OVERVIEW

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/O
subsystems. The 3B Series Subsystem consists of a 10” 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 single­ended 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 +10V
(or +

10V) and 4-20 mA (or 0-20 mA).

3B20

FUNCTIONAL BLOCK DIAGRAM

Figure 1. 3B20 Functional Block Diagram

Output modules accept 0 to +10V (or +10V) 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
used for analog transmission, operator interface, or an analog
backup system.

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 +
modules), and feature two high-level analog outputs that are
compatible with most process instrumentation. The isolated
input modules also provide +

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.

0.1%, low drift of +1 uV/oC (low-level input

1500 V peak isolation.

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable.
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: [phone]
Fax: [phone] © 2004 Analog Devices, Inc. All rights reserved.

www.analog.com

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GENERAL DESCRIPTION

The 3B20 is a wideband single-channel signal-conditioning
module which interfaces 4-arm AC bridge transducer signals
ranging between 1.5mV rms and 150mV rms, providing
simultaneous precision voltage and current outputs. In addition,
the module provides an AC excitation voltage of 2V rms to 10V
rms at frequencies between 1kHz and 10kHz. The module
withstands 130V rms at its current output terminals without
damage thereby shielding computer-side circuitry from field­side over-voltage conditions. The 3B20 is a plug-in, mix-and­match, hot-swappable module and is easily field calibrated via
front-panel zero and span adjustments for both voltage and
current outputs.

3B Series Custom-Ranging Program – Externally­programmable Model 3B20-00, enables the user to configure a
special input range, including tare weight suppression, by using
the optional plug-on AC1310 ranging card, which houses user­supplied resistors to determine zero and span. To facilitate

.

3B20

selecting resistors, a Windows program, 3B-CUSTOM,
calculates resistor values based on the user-desired input/output
ranges.

The 3B20 input and AC bridge excitation output terminals are
protected for up to 130V rms. The excitation amplitude and
frequency can be specified with the Model 3B20 CUSTOM or
user configured with Model 3B20-00 and an optional plug-on
Model AC1310 ranging card. Both the voltage and current
outputs can be independently adjusted for a minimum of +
for the zero and 25% of the span range with front-panel user­accessible potentiometers. In addition, phase shifts of up to

o

37.25

between excitation signal and the output signal from the
strain gauge or torque transducer can be compensated via front­panel screw terminal adjustments.

1V

Figure 2

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Rev. 0 | Page 2 of 8

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3B20 Models Available

Model Excitation

3B20-00

3B20-01

3B20-Custom

1

Output current range may be user programmed to 4 mA to 20 mA using jumper supplied.

2

Requires AC1310 ranging card.

* Custom Input/Output ranges are available. Refer to configuration guide.

Voltage

Externally

Programmable2

5 V rms 3 kHz 20 mV rms 2 mV rms/V -10 V to +10 V &

* * * * *

3B20 Specifications
(typical @ +25°C and ±15 V dc, and +24 V dc Power)

Description Model 3B20

Standard Range Refer to Model Table

Custom Ranges Vin = 1.5 mV rms to 150 mV rms

Voltage (RL > 2 KΩ)

Current (RL = 0 to 850Ω)1

With Input Overload 40 mA, maximum

Initial @ +25°C ±0.1% Span

2

Nonlinearity

Voltage Output

Zero ±0.005% of Span/°C

Span ±0.01% of Span/°C

Current Output

Zero ±25 ppm of Span/°C

Span ±25 ppm of Reading/°C

Vol ta ge

Voltage, tolerance ±2.5%

Frequency

Drive Up to 20 mA rms, minimum

Harmonic Distortion < 0.5%

Span Calibration Adjustment Range4

±0.05% Span

3

4

2 V rms to 10 V rms

4

1 kHz to 10 kHz, ±15%

Excitation

Frequency

Externally

Programmable2

Stability vs. Temperature

Input Range Sensitivity Output

Programmable2

Input Range

Output Range

Accuracy2

Bridge Excitation

Externally

V

= 2 V rms to 10 V rms

exc

V

freq. = 1 kHz to 10 kHz

exc

-10 V to +10 V

4 mA to 20 mA or 0 mA to 20 mA

±25% of span, minimum

Programmable2

Externally

3B20

Ranges1

-10 V to +10 V &
0 mA to 20 mA

0 mA to 20 mA

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