5B38 Isolated, Wide-Bandwidth Strain Gage Input


Model 5B38-02The 5B38 is a wide-bandwidth single-channel signal conditioning module that interfaces, amplifies, and filters signals from full-bridge and half-bridge strain-gage transducers between 300 Ω and 10 kΩ. The module provides an isolated bridge excitation of +10 V and a protected, isolated precision output of -5 V to +5 V. The 10 kHz bandwidth of the module ideally suits to measure signals that vary rapidly with time, such as strain on an automobile chassis during a crash test.

The 5B38 protects the computer side from damage due to field-side overvoltage faults. The module withstands 240 V rms at its input terminals without damage, thereby shielding computer-side circuitry from field-side overvoltage conditions. In addition, the 5B38 is mix-and-match and hot-swappable with all 5B Series modules, so can be inserted or removed from any socket in the same backplane without disrupting system power.

The 5B38-04 contains bridge completion circuitry, so can function with half-bridge strain gages. For quarter-bridge requirements, the user must complete the bridge input to the half-bridge level externally. The factory can configure the module for a wide range of input ranges (sensitivities).

Inside the 5B38 Module

A single-pole anti-aliasing filter resides at each modules input. A three-pole, low-pass filter in the output stage sets the bandwidth and yields optimal noise performance for accurate measurement of small signals in high electrical noise. A chopper-stabilized input amplifier provides low drift and stable gain.

Signal isolation by transformer coupling uses a proprietary modulation technique for linear, stable and reliable performance. The differential input circuit on the field side is fully floating, eliminating the need for any input grounding. A demodulator on the computer side of the signal transformer recovers the original signal, which is then filtered and buffered to provide a low-noise, low-impedance output signal. An additional benefit, the output section acts as a third floating port, eliminating possible problems from ground loops and power-supply noise. The output common must be kept within ±3 V of power common.

Convenience Features

A series output switch eliminates the need for external multiplexing in many applications. The switch is turned on by an active-low enable input. The enable input should be grounded to power common if the output need not be switched, as on the 5B01 and 5B08 backplanes.

Input and Output Ranges

5B38 Functional Block Diagram

Figure 1. 5B38 Functional Block Diagram

5B38 Input Field Connections
Figure 2. 5B38 Input Field Connections

Input Type

Strain Gage: Full-Bridge/Half-Bridge

Output Ranges
-5 V to +5 V

5B38 Models Available

Model  Input
Bridge Type
Excitation Sensitivity Output Range
Order Now 5B38-02
Full Bridge
300 Ω to 10 kΩ +10.0 V
3 mV/V
-5 V to +5 V
Order Now
Half Bridge
300 Ω to 10 kΩ
+10.0 V 3 mV/V
-5 V to +5 V
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Full Bridge
300 Ω to 10 kΩ
+10.0 V
2 mV/V
-5 V to +5 V

5B38-Custom * 300 Ω to 10 kΩ
+10.0 V
* -5 V to +5 V

* Custom Input/sensitivity ranges are available. Refer to configuration guide.

5B38 Specifications

Description  Model 5B38 Full Bridge Model 5B38 Half Bridge
Input Ranges
Standard Ranges
±20 mV (2 mV/V Sensitivity)
±30 mV (3 mV/V Sensitivity)
±30 mV (3 mV/V Sensitivity)
Custom Ranges
±10 mV to ±500 mV *
Output Ranges (RL > 50 kΩ)
-5 V to +5 V *
Initial @ +25°C
±0.08% Span ±10 µV RTI
±0.08% Span ±1 mV RTI
±0.02% Span
Input Offset vs. Temperature
±1 µV/°C
Output Offset vs. Temperature
±40 µV/°C
Gain vs. Temperature
±25 ppm of Reading/°C *
Excitation Voltage Output @ full load +10 V ±3 mV
Load Range
10 kΩ, minimum; 300 Ω, maximum *
Load Regulation
±5 ppm/mA
vs. Temperature
±15 ppm/°C
Half Bridge Voltage Level
+5 V ±1 mV
Half Bridge Voltage vs. Temperature
N/A ±15 ppm/°C
Input Bias Current
±3 nA
Input Resistance
Power On 20 MΩ, minimum
Power Off 40 kΩ, minimum
Overload 40 kΩ, minimum *
Input, 0.1 Hz to 10 Hz Bandwidth
0.4 µV rms
Input, 10 kHz Bandwidth ±70 nV/√Hz
±250 nV/√Hz
Output, 100 kHz Bandwidth
10 mV peak-peak *
Bandwidth, -3 dB 10 kHz *
Output Rise Time, 10% to 90% Span
40 µs
Output Settling Time, to 0.1%
250 µs
7 ms
Common-Mode Voltage (CMV)
Input-to-Output, Continuous
1500 V rms, maximum
Output-to-Power, Continuous2
250 V rms, maximum
Transient ANSI/IEEE C37.90.1-1989 *
Common-Mode Rejection (CMR)
1 kΩ Source Imbalance, 50/60 Hz
100 dB
Normal Mode Rejection, 50/60 Hz
-3 dB @ 10 kHz *
Input Protection, Signal and Excitation Voltage
240 V rms maximum
ANSI/IEEE C37.90.1-1989
Output Resistance
50 Ω
Voltage Output Protection
Continuous Short to Ground
Output Selection Time
6 µs @ Cload = 0 to 2,000 pF
Output Enable Control
Max Logic "0"  +1 V *
Min Logic "1"
+2.5 V
Max Logic "1"
+36 V
Input Current "0"
0.4 mA *
Power Supply Voltage
+5 V ±5%
Power Supply Current 200 mA, Full Load; 120 mA, No Load
Power Supply Sensitivity, RTI
25 ppm reading/% ±2.5µV RTI/%
Mechanical Dimensions
2.275" x 2.375" x 0.595"
(57.8 mm x 59.1 mm x 15.1 mm)
Temperature Range
   Rated Performance -25°C to +85°C
   Operating -40°C to +85°C *
   Storage -40°C to +85°C
Relative Humidity
0 to 93% @ +40°C noncondensing
RFI Susceptibility
±0.5% Span error @ 400 MHz, 5 Watt, 3 ft *

* Same as full-bridge version. 
1 Includes the combined effects of repeatability, hysteresis, and nonlinearity. Loads heavier than
50 kΩ will degrade nonlinearity and gain temperature coefficient. 
2 The output common must be kept within ±3 V of power common.

Specifications subject to change without notice.