Functional Description

7B31-01-1 The 7B31 is a single-channel signal conditioning module that interfaces, amplifies and filters unipolar and bipolar voltage inputs and provides a protected precision output of either +1 V to +5 V or 0 V to +10 V. Model 7B31 features a nonlinearity of ±0.02% maximum and an accuracy of ±0.1% maximum (±0.01% typical). 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 120 dB @ 50/60 Hz and a normal mode rejection (NMR) of 60 dB @ 50/60 Hz are provided. Rated to operate with a nominal +24 V DC supply, Model 7B31 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.

Inside the 7B31 Series Module

The floating differential input of Model 7B31 is fully protected up to 120 V rms line voltage. A one-pole 3 Hz filter preconditions the input signal prior to amplification by a low drift input (1500 V rms input-to-output and power). Isolated front-end circuitry power is supplied by a DC/DC converter. The output section contains a two-pole low pass filter (-3 dB @ 3Hz), a buffer amplifier and a 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 of 2 kΩ minimum.

7B31 FBD

Figure 1. 7B31 Functional Block Diagram


Input Types

±5 V to ±50 V

Output Options

+1 V to +5 V

0 V to +10 V


Figure 2. 7B31 Input Field Connections

7B31 Models Available
  Model Input Range Output Range
Order Now 7B31-01-1 0 V to +10 V +1 V to +5 V
Order Now 7B31-01-2 0 V to +10 V 0 V to +10 V
Order Now 7B31-02-1 -5 V to +5 V +1 V to +5 V
Order Now 7B31-02-2 -5 V to +5 V 0 V to +10 V
Order Now 7B31-03-1 -10 V to +10 V +1 V to +5 V
Order Now 7B31-03-2 -10 V to +10 V 0 V to +10 V
Order Now 7B31-04-1 0 V to +5 V +1 V to +5 V
Order Now 7B31-04-2 0 V to +5 V 0 V to +10 V
Order Now 7B31-05-1 0 V to +20 V +1 V to +5 V
Order Now 7B31-05-2 0 V to +20 V 0 V to +10 V
Order Now 7B31-06-1 -20 V to +20 V +1 V to +5 V
Order Now 7B31-06-2 -20 V to +20 V 0 V to +10 V
Order Now 7B31-07-1 0 V to +50 V +1 V to +5 V
Order Now 7B31-07-2 0 V to +50 V 0 V to +10 V
Order Now 7B31-08-1 -50 V to +50 V +1 V to +5 V
Order Now 7B31-08-2 -50 V to +50 V 0 V to +10 V

7B31 Specifications
(typical @ +23°C ±5°C and Vs = +24 V dc)

Description Model 7B31
Input Ranges (Refer to Model Table)
Standard Unipolar Ranges 0 V to: +5 V or +10 V or +20 V or +50 V
Standard Bipolar Ranges ±5 V or ±10 V or ±20 V or ±50 V
Custom Ranges Not Available*
Output Range Options (RL > 2 kΩ) +1 V to +5 V or 0 V to +10 V
Initial @ +25°C ±0.01% Span (±0.1% Span, maximum)
Nonlinearity2 ±0.02% Span, maximum
Input Offset vs. Temperature ±0.5µV/°C
Zero Suppression vs. Temperature ±0.005% (Vz)3/°C
Span vs. Temperature ±35 ppm/°C
Output Offset vs. Temperature ±0.002% span/°C
Input Resistance
Power ON
7B31-01 to 7B31-04 100 kΩ
7B31-05 to 7B31-08 1 MΩ
Power OFF 30 kΩ, minimum
Output Noise
5 MHz Bandwidth 6 mV peak
10 Hz to 100 kHz Bandwidth 0.4 mV rms
0.1 Hz to 10 Hz Bandwidth 3 µV peak
Bandwidth, -3 dB 3 Hz
Output Rise Time, 10% to 90% Span 150 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 120 dB
Normal Mode Rejection @ 50/60 Hz 120 dB
Input Protection 120 V rms, continuous
±35 V dc, continuous
Input Transient Protection ANSI/IEEE C376.90.1-1989
IEC 255-4, Class II
Output Resistance < 1 Ω
Voltage Output Protection Continuous Short to Ground
Power Supply
Voltage Range, Operating +14 V dc to +35 V dc
Current +25 mA, maximum
Sensitivity ±0.0001%/% of Vs
Mechanical Dimensions 1.663" x 2.11" x 0.563"
(42.24 mm x 53.6 mm x 14.3 mm)
Weight 60 grams
Temperature Range
   Operating -40°C to +85°C
   Storage -40°C to +85°C
Relative Humidity, 24 hours 0 to 90% @ +60°C noncondensing
ESD Sensitivity IEC 801-2, Level 2
RFI Susceptibility ±0.5% Span error @ 400 MHz, 5 Watt, 3 ft
Warm-up time required to meet specifications is approximately 10 minutes.
* Contact factory for OEM requirements.
1Includes the combined effects of repeatability, hysteresis, and nonlinearity.
2Nonlinearity is calculated using best-fit straight line method.
3Vz is the nominal input voltage that results in a 0 V output.
Specifications subject to change without notice.
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