Analog Devices B35 Datasheet

Isolated Process Current Input

FEATURES

Single-channel signal conditioning current input module
that interfaces with two-wire transmitters.

Module provides a precision output of either +1 V to +5 V or
+2 V to +10 V, linear with temperature.

Features a isolated 24 VDC loop supply for driving the
transmitter.

All 7B35 series modules are mix-and-match and Hot
Swappable.

APPLICATIONS

Industrial signal isolation
Industrial signal filtering

PRODUCT OVERVIEW

The 7B Series of signal conditioners feature small size, low cost
and a wide output voltage range for a variety of applications
including process control and factory-floor environments. The
single-channel 7B modules accept inputs from a range of
transducers and are fully rated over the extended -40

o

C industrial temperature range. All 7B Series modules are

+85
rated for a nominal power supply input of +24 VDC; and, for
maximum flexibility, they will accept supply voltages in the +14
VDC to +35 VDC range. The input modules, with the exception
of the 7B21, provide a high-level output voltage that is factory
configured for either the +1 V to +5 V or 0 V to +10 V range.
The 7B21 is a unity gain, isolated input module with an
input/output range of +10V. Output modules are available that
provide either isolated process current or isolated bipolar
voltage output. Model 7B39 converts either a +1 V to +5 V input
to a 4 to 20 mA output or a 0 V to +10 V input to a 0-20 mA
output. The input/output ranges of the 7B39 are factory
configured. The 7B22 is a unity gain module that provides an
isolated +10V output signal. All modules have a universal pin­out and may be readily hot-swapped under full power without
disrupting field wiring. Each module accepts analog transducer
signals and transfers them to a process control or factory data
collection system without the inherent noise, non-linearity, drift
and extraneous voltages which frequently accompany the
signals.

o

C to

with Loop Power

7B35

FUNCTIONAL BLOCK DIAGRAM

Figure 1. 7B35 Functional Block Diagram

The modules feature a maximum nonlinearity of +0.02% and
are factory calibrated to guarantee a maximum accuracy
specification of +

The 7B Series offers up to 1500 V rms continuous common
mode voltage isolation and 120 V rms of field wiring input
protection. The power supplies necessary to drive each of the
individual module’s input circuitry are internally isolated,
enabling the 7B Series modules to offer true channel-to-channel
isolation of the input signals.

The modules directly accept analog signals from
thermocouples, RTDs, current loop powered transmitters, and
other process control signals. The 7B Series modules amplify,
linearize, isolate, protect and convert the transducer output
signals to standardized analog inputs for high-level analog I/O
subsystems. The 7B Series Subsystem consists of 19-inch rack­compatible hardware (model AC 1363), with universal
mounting backplane and a family of plug-in (up to 16 per
backplane) input and output signal conditioning modules. Four­, eight-, and sixteen-channel backplanes are available. Each
backplane incorporates screw terminals for easy power
connections and field wiring, and includes a 25-pin D-type
connector for interfacing the high-level single-ended voltage
outputs to the user’s equipment. Gold-plated sockets are
provided on each channel of the backplane to ensure the
reliability of each module’s electrical connection.

0.1%.

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GENERAL DESCRIPTION

The 7B35 is a single-channel signal conditioning current input
module that interfaces with two-wire transmitters, providing an
isolated protected precision output of either +1 V to +5 V or +2
V to +10 V. Model 7B35 features an isolated 24 VDC loop power
supply for driving the transmitter. To accurately measure low
level signals in electrically noisy environments, 1500 V rms of
galvanic transformer-based isolation with a common mode
rejection (CMR) of 105 dB @ 50/60 Hz is provided. Rated to
operate with a nominal +24 VDC supply, Model 7B35 is mix­and-match and hot-swappable with other 7B Series input
modules, so it can be inserted or removed from any socket in
the same backplane without disturbing system power.

The two input pins of Model 7B35 are each fully protected up to
120 V rms. The current input signal is converted to a voltage,
then filtered by a one-pole 100 Hz filter. Amplitude modulation
is used to implement transformer isolation (1500 V rms input­to-output and power). Isolated front-end circuitry power is
supplied by a DC/DC converter. The isolated transmitter loop
power supply is unregulated and will provide a voltage that is
proportional to the voltage used to power the 7B35 module. The

7B35

isolated voltage provided by the 7B35 is between 13 VDC and
34 VDC for loop currents between 4 mA and 20 mA and supply
voltages between 20.4 VDC and 26.4 VDC. The output section
contains a two-pole low-pass filter (-3 dB @ 100 Hz), a buffer
amplifier and power oscillator. The two-pole output filter and
subsequent buffer ensures that a low noise, low impedance
(<1Ω) signal is available at the output to drive loads down to
2kΩ.

Figure 2

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7B35

7B35 Models Available

Model Input Range Output Range

7B35-01-1
7B35-01-2

+4 mA to +20 mA
+4 mA to +20 mA1 +2 V to +10 V

1

+1 V to +5 V

7B35 Specifications
(typical @ +23°C ±5°C and Vs = +24 V dc)

Description Model 7B35

Input Range1

Standard Range 4 mA to 20 mA
Custom Ranges Not Available*
Standard Range 4 mA to 20 mA
Custom Ranges Not Available*
Input Loop Supply Voltage, Isolated +24 V dc @ I
Output Range (RL > 2 kΩ)

Initial @ +25°C ±0.01% Span (±0.1% Span, maximum)
Nonlinearity2 ±0.02% Span, maximum
Input Offset vs. Temperature N/A3
Span vs. Temperature ±40 ppm/°C
Output Offset vs. Temperature ±0.003% span/°C

5 MHz Bandwidth 6 mV peak
10 Hz to 100 kHz Bandwidth 0.9 mV rms

0.1 Hz to 10 Hz Bandwidth 4 µV peak
Bandwidth, -3 dB 100 Hz
Output Rise Time, 10% to 90% Span 5 ms

Common-Mode Voltage (CMV)

Input-to-Output and Power 1500 V rms continuous

Common Mode Rejection (CMR)

Input-to-Output and Power @ 50/60 Hz 105 dB
Input Protection 120 V rms, continuous

Input Transient Protection ANSI/IEEE C376.90.1-1989

+1 V to +5 V or +2 V to +10 V

Accuracy1

Output Noise

±35 V dc, continuous

IEEE-STD 472
IEC 255-4, Class II

= 20 mA

Loop

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