ANALOG DEVICES 3B37 Service Manual

Isolated, Thermocouple Input

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FEATURES

Interfaces, amplifies, & filters input voltages from a J, K, T, E,
R, S, or B-type thermocouple.

High accuracy internal cold junction compensation.
Module provides simultaneous precision voltage and

current outputs.
Current output withstands 130V rms without damage.
All 3B37 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).

3B37

FUNCTIONAL BLOCK DIAGRAM

Figure 1. 3B37 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 sysem 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 3B37 is a single-channel signal conditioning module that
interfaces, amplifies and filters input voltages from a J, K, T, E, R,
S or B-type thermocouple and provides isolated simultaneous
voltage and current outputs linear with input voltage. High
accuracy internal cold junction compensation and a predictable
upscale open circuit indication provide a complete signal
conditioning solution. To accurately measure low level signals
in electrically noisy environments, +
transformer-based isolation with a common mode rejection
(CMR) of 160 dB @ 50/60 Hz and a normal mode rejection
(NMR) of 60 dB @ 50/60 Hz are provided. The current output
withstands 130 V rms without damage and interfaces user
equipment through screw terminals located on the 3B Series
backplane. This plug-in, mix-and-match, hot-swappable module
is easily field calibrated via front-panel zero and span
adjustments for both voltage and current outputs.

Accurate and System Ready – Internal cold-junction
compensation largely corrects errors arising from parasitic
thermocouples formed by thermocouple connection to the
input screw terminals, providing an accuracy of +

o

C to +45oC ambient temperature range. The module

+5
generates a predictable upscale signal to indicate an open
thermocouple; for a downscale response, connect a 47MΩ, 0.25
Watt resistor across screw terminals 2 and 4 on the 3B Series
backplane

3B Series Custom Ranging Program – Externally­programmable version Model 3B37-X-00, enable the user to
configure a special input range by using the optional plug-on

.

1500 V peak of galvanic

0.5oC over the

3B37

AC1310 ranging card, which houses user-supplied resistors to
determine zero and span. To facilitate selecting resistors, a
Windows program, 3B-Custom, calculates resistor values based
on the user-desired input/output ranges.

Inside the 3B37 Module – A chopper-stabilized low-drift input
amplifier assures stable long-term stability. At the amplifier
input, a zero-scale input voltage is subtracted from the input
signal to set the zero-scale value. For user convenience, the zero
and span optionally can be factory configured to meet custom
needs (Model 3B37-CUSTOM) or can be externally
programmed (Model 3B37-X-00) via user-supplied resistors
inserted in the optional AC1310 plug-on ranging card. Zero
suppression can exceed 100% of the input range. This enables
suppression of a zero-scale input value amny times larger that
the total span for precise expanded-scale measurements of a
selection portion of an input signal. The differential input
circuit on the field side is fully floating, eliminating the need for
any input grounding. Signal isolation by transformer coupling
users a proprietary modulation technique for linear, stable and
reliable performance. A demodulator on the computer side of
the signal transformer recovers the original signa, which is then
filtered and buffered to provide a low-noise, low-impedance
output voltage, this output also drives a voltage-to-current (V/I)
converter to provide a simultaneous current output for
interfacing versatility.

Rev. 0 | Page 2 of 8

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Figure 2

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3B37

3B37 Models Available

Model Input Type Input Range Output Ranges1

3B37-X-00

3B37-J-01

3B37-K-02

3B37-T-03

3B37-E-04

3B37-R-05

3B37-S-05

3B37-B-06

3B37-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.

Type J, K, T, E, R, S, or B Externally Programmable

Type J -100°C to +100°C (-148°F to +1400°F) 0 V to +10 V & 0 mA to 20 mA

Type K -100°C to +1350°C (-148°F to +2462°F) 0 V to +10 V & 0 mA to 20 mA

Type T -100°C to +400°C (-148°F to +752°F) 0 V to +10 V & 0 mA to 20 mA

Type E 0°C to +900°C (+32°F to +1652°F) 0 V to +10 V & 0 mA to 20 mA

Type R 0°C to +1750°C (+32°F to +3182°F) 0 V to +10 V & 0 mA to 20 mA

Type S 0°C to +1750°C (+32°F to +3182°F) 0 V to +10 V & 0 mA to 20 mA

Type B 0°C to +1800°C (+32°F to +3272°F) 0 V to +10 V & 0 mA to 20 mA

Type J, K, T, E, R, S, or B * *

2

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

3B37 Specifications

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

Description Model 3B37

Input Ranges

Standard Ranges Refer to Model Table

Custom Ranges ±5 mV to ±500 mV

Output Ranges

Voltage (RL > 2 KΩ)

Current (RL = 0 to 850Ω)1

Maximum Current Output Span 0 mA to 31 mA

Initial @ +25°C ±0.1% Span + CJC Sensor Error

Nonlinearity ±0.01% Span

Stability vs. Temperature

Voltage Output

Zero ±0.02°C/°C

Span ±25 ppm of Reading/°C

Current Output

Zero ±25 ppm of Span/°C

Span ±25 ppm of Reading/°C

Zero and Span Adjustment Range4

Cold Junction Compensation (CJC)

Initial Accuracy @ +25°C ±0.5 °C

Accuracy vs. Temperature, +5°C to +45°C ±0.5°C (±0.0125°C/°C)

Input Bias Current

3

5

0 V to +10 V; -10 V to +10 V

4 mA to 20 mA or 0 mA to 20 mA

2

Accuracy

±5% of Span

+15 nA

Rev. 0 | Page 3 of 8