Isolated Process Current Input
with Loop Power
7B35
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.
FUNCTIONAL BLOCK DIAGRAM
APPLICATIONS
Industrial signal isolation
Industrial signal filtering
Figure 1. 7B35 Functional Block Diagram
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 to
+85
o
C industrial temperature range. All 7B Series modules are
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 pin-
out 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.
The modules feature a maximum nonlinearity of +0.02% and
are factory calibrated to guarantee a maximum accuracy
specification of +0.1%.
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 rack-
compatible 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.
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.
www.analog.com
Tel: 781.329.4700
Fax: 781.326.8703
© 2004 Analog Devices, Inc. All rights reserved.
7B35
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 mix-
and-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 input-
to-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
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
Rev. 0 | Page 2 of 8
7B35
7B35 Models Available
Model
7B35-01-1
7B35-01-2
Input Range
+4 mA to +20 mA
1
+4 mA to +20 mA
1
+1 V to +5 V
+2 V to +10 V
Output Range
7B35 Specifications
(typical @ +23°C ±5°C and V
s
= +24 V dc)
Description
Input Range1
Standard Range
Custom Ranges
Standard Range
Custom Ranges
Input Loop Supply Voltage, Isolated
Output Range (R
L
> 2 kΩ)
4 mA to 20 mA
Not Available*
4 mA to 20 mA
Not Available*
+24 V dc @ I
Loop
= 20 mA
+1 V to +5 V or +2 V to +10 V
Accuracy1
Initial @ +25°C
Nonlinearity
2
Input Offset vs. Temperature
Span vs. Temperature
Output Offset vs. Temperature
±0.01% Span (±0.1% Span, maximum)
±0.02% Span, maximum
N/A
3
±40 ppm/°C
±0.003% span/°C
Output Noise
5 MHz Bandwidth
10 Hz to 100 kHz Bandwidth
0.1 Hz to 10 Hz Bandwidth
Bandwidth, -3 dB
Output Rise Time, 10% to 90% Span
6 mV peak
0.9 mV rms
4 µV peak
100 Hz
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
Input Protection
Input Transient Protection
105 dB
120 V rms, continuous
±35 V dc, continuous
ANSI/IEEE C376.90.1-1989
IEEE-STD 472
IEC 255-4, Class II
Model 7B35
Rev. 0 | Page 3 of 8
7B35
Output Resistance
Voltage Output Protection
<1
Ω
Continuous Short to Ground
Power Supply
Voltage Range, Operating
Current
Sensitivity
Mechanical Dimensions
Weight
+14 V dc to +35 V dc
+25 mA, maximum
±0.0001%/% of Vs
1.663" x 2.11" x 0.563"
(42.24 mm x 53.6 mm x 14.3 mm)
60 grams
Environmental
Temperature Range
Operating
Storage
Relative Humidity, 24 hours
ESD Sensitivity
RFI Susceptibility
Warm-up time required to meet specifications is approximately 10 minutes.
* Contact factory for OEM requirements.
1
Includes the combined effects of repeatability, hysteresis, and nonlinearity.
2
Nonlinearity is calculated using best-fit straight line method.
3
Input offset term is included in the output offset specification.
Specifications subject to change without notice.
-40°C to +85°C
-40°C to +85°C
0 to 90% @ +60°C non-condensing
IEC 801-2, Level 2
±0.5% Span error @ 400 MHz, 5 Watt, 3 ft
Rev. 0 | Page 4 of 8
7B35
PIN CONFIGURATIONS AND FUNCTIONAL DESCRIPTIONS
Figure 3 7B35 Input Field Connections
Table 1. Pin Function Descriptions—
Pin
No.
0
1
2
3
4
5
Input Module Function
SENSOR INPUT
INPUT HIGH
INPUT LOW
POWER SUPPLY (DC)
OUTPUT VOLTAGE
OUTPUT & POWER
COMMON
Output Module Function
NOT USED
OUTPUT HIGH
OUTPUT LOW
POWER SUPPLY (DC)
INPUT VOLTAGE
INPUT AND POWER
COMMON
Figure 4 . Model 7B Series Module, with pin-out assignments.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human
body and test equipment and can discharge without detection. Although this product features proprietary ESD
protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges.
Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. 0 | Page 5 of 8
