Isolated Process Current Input
with Loop Power
7B35
FEATURES |
FUNCTIONAL BLOCK DIAGRAM |
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Single-channel signal conditioning current input module |
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that interfaces with two-wire transmitters. |
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Module provides a precision output of either +1 V to +5 V or |
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+2 V to +10 V, linear with temperature. |
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Features a isolated 24 VDC loop supply for driving the |
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transmitter. |
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All 7B35 series modules are mix-and-match and Hot |
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Swappable. |
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APPLICATIONS |
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Industrial signal isolation |
Figure 1. 7B35 Functional Block Diagram |
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Industrial signal filtering |
The modules feature a maximum nonlinearity of +0.02% and |
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are factory calibrated to guarantee a maximum accuracy |
PRODUCT OVERVIEW |
specification of +0.1%. |
The 7B Series of signal conditioners feature small size, low cost |
The 7B Series offers up to 1500 V rms continuous common |
and a wide output voltage range for a variety of applications |
mode voltage isolation and 120 V rms of field wiring input |
including process control and factory-floor environments. The |
protection. The power supplies necessary to drive each of the |
rated for a MacshbM |
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single-channel 7B modules accept inputs from a range of |
individual module’s input circuitry are internally isolated, |
transducers and are fully rated over the extended -40oC to |
enabling the 7B Series modules to offer true channel-to-channel |
+85oC industrial temperature range. All 7B Series modules are |
isolation of the input ignals. |
nominal power supply input of +24 VDC; and, for maximum flexibility, they will accept supply voltages in the +14
The modules directly accept analog signals from
VDC to +35 VDC range. The input modules, with the exception
thermocouples, RTDs, current loop powered transmitters, and
of the 7B21, provide a high-level output voltage that is factory
other process control signals. The 7B Series modules amplify,
configured for either the +1 V to +5 V or 0 V to +10 V range.
linearize, isolate, protect and convert the transducer output
The 7B21 is a unity gain, isolated input module with an
signals to standardized analog inputs for high-level analog I/O
input/output range of +10V. Output modules are available that
subsystems. The 7B Series Subsystem consists of 19-inch rack-
provide either isolated process current or isolated bipolar
compatible hardware (model AC 1363), with universal
voltage output. Model 7B39 converts either a +1 V to +5 V input
mounting backplane and a family of plug-in (up to 16 per
to a 4 to 20 mA output or a 0 V to +10 V input to a 0-20 mA
backplane) input and output signal conditioning modules. Four-
output. The input/output ranges of the 7B39 are factory
, eight-, and sixteen-channel backplanes are available. Each
configured. The 7B22 is a unity gain module that provides an
backplane incorporates screw terminals for easy power
isolated +10V output signal. All modules have a universal pin-
connections and field wiring, and includes a 25-pin D-type
out and may be readily hot-swapped under full power without
connector for interfacing the high-level single-ended voltage
disrupting field wiring. Each module accepts analog transducer
outputs to the user’s equipment. Gold-plated sockets are
signals and transfers them to a process control or factory data
provided on each channel of the backplane to ensure the
collection system without the inherent noise, non-linearity, drift and extraneous voltages which frequently accompany the signals.
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.
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.
MacshbM
Figure 2
Rev. 0 | Page 2 of 8
7B35
7B35 Models Available
Model |
Input Range |
Output Range |
7B35-01-1 |
+4 mA to +20 mA1 |
+1 V to +5 V |
7B35-01-2 |
+4 mA to +20 mA1 |
+2 V to +10 V |
7B35 Specifications
(typical @ +23°C ±5°C and Vs = +24 V dc)
Description |
Model 7B35 |
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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 @ ILoop = 20 mA |
MacshbM |
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Output Range (RL > 2 kΩ) |
+1 V to +5 V or +2 V to +10 V |
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Accur cy1 |
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 |
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Output Noise |
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 |
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Common-Mode Voltage (CMV) |
Input-to-Output and Power |
1500 V rms continuous |
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Common Mode Rejection (CMR) |
Input-to-Output and Power @ 50/60 Hz |
105 dB |
Input Protection |
120 V rms, continuous |
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±35 V dc, continuous |
Input Transient Protection |
ANSI/IEEE C376.90.1-1989 |
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IEEE-STD 472 |
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IEC 255-4, Class II |
Rev. 0 | Page 3 of 8
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