3B18 Wide-Bandwidth, Strain Gage Input


Model 3B18-01The 3B18 is a wideband (20 kHz) single-channel signal conditioning module which interfaces, amplifies, and filters signals from balanced 4-arm full-bridge strain-gage bridges with a resistance from 100 Ω to 10 kΩ, providing simultaneous precision voltage and current outputs. The module provides two user-selectable (via front-panel switches) bridge excitation voltages: +10 V for bridges with a load impedance down to 300 Ω or +3.33 V for 120 Ω bridges or others below 300 Ω. Module bandwidth is also user-selectable between 20 kHz and 100 Hz, with user-supplied filter capacitors installed in the optional AC1310 ranging card. The 3B18 protects the computer side from damage due to field-side overvoltage faults up to 130 V rms. In addition, the current output withstands 130 V rms without damage and interfaces user equipment through screw terminals located on the 3B Series backplane. The 3B18 is a plug-in, mix-and-match, hot-swappable module which is easily field calibrated via front-panel zero and span adjustments for both voltage and current outputs.

3B Series Custom-Ranging Program

Externally-programmable Model 3B18-00, enables the user to configure a special input range by using the optional plug-on AC1310 ranging card, which houses user-supplied resistors to determine zero and span. To facilitate selecting resistors, a Windows® program, 3B-CUSTOM, calculates resistor values based on the user-desired input/output ranges.

Inside the 3B18 Series Module

A chopper-stabilized low-drift (±1µV/°C) input amplifier assures stable long-term stability. For user convenience, the zero and span can be factory configured to meet custom range needs (Model 3B18-CUSTOM) or can be externally programmed (Model 3B18-00) via user supplied resistors inserted in the optional AC1310 plug-on ranging card.

Input and Output Ranges

3B18 Functional Block Diagram
Figure 1. 3B18 Functional Block Diagram

3B18 Input Field Connections
Figure 2. 3B18 Input Field Connections

Input Type
Dual Outputs
Strain Gage:
-10 V to +10 V
Full 4-Arm Bridge
4 mA to 20 mA or 0 to 20 mA

3B18 Models Available

Model  Input 
Excitation1 Sensitivity Output 
Order Now 3B18-00
Full Bridge Externally
+10.0 V or +3.33 V Externally
-10 V to +10 V &
0 mA to 20 mA
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Full Bridge
-30 mV to +30 mV
+10.0 V or +3.33 V
3 mV/V @ 10 Vexc -10 V to +10 V &
0 mA to 20 mA
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Full Bridge
2.5 kHz +10.0 V or +3.33 V 3 mV/V @ 3.33 Vexc -10 V to +10 V &
0 mA to 20 mA

Full Bridge
5 kHz
+10.0 V or +3.33 V
* *

1 Output current range may be user programmed to 4 mA to 20 mA using jumper supplied.
2 Requires AC1310 ranging card.
* Custom Input/Output ranges are available. Refer to configuration guide.

3B18 Specifications

(typical @ +25°C and ±15 V dc, and +24 V dc Power)

Description  Model 3B18
Input Range
Standard Range
±30 mV (3 mV/V sensitivity @ Vexc = +10V)
±10 mV (3 mV/V sensitivity @ Vexc = +3.33 V)
Custom Ranges
±5 mV to ±500
Output Range
Voltage (RL > 2 KΩ)
-10 V to +10 V
Current (RL = 0 to 850Ω)1
4 mA to 20 mA or 0 mA to 20 mA
   Maximum Current Output Span
0 mA to 31 mA
Initial @ +25°C
±0.1% Span
±0.01% Span
Stability vs. Temperature
Voltage Output
   Zero ±3 µV/°C (RTI)
   Span ±25 ppm of Reading/°C
Current Output3
   Zero ±25 ppm of Span/°C
   Span ±25 ppm of Reading/°C
Bridge Excitation
Voltage user-selectable
+10 V or +3.33 V
Voltage, tolerance
Voltage vs. Temperature ±0.0015%/°C
 Bridge Resistance Range
Vexc= +10.0 V 300 Ω to 1 kΩ
Vexc = +3.33 V 100 Ω to 10 kΩ
Zero and Span Adjustment Range4
±5% of Span
Input Bias Current
+25 nA
Input Resistance
100 MΩ
Bandwidth, -3 dB
20 kHz
Output Rise Time, 10% to 90% Span
Common Mode Voltage (CMV)
Input-to-Output, Continuous
±10 V peak, maximum
ANSI/IEEE C37.90.1- 1989
 Common Mode Rejection (CMR)
 1 kΩ Source Imbalance, 50/60 Hz  100 dB
Input Protection, Signal and Excitation Voltage
130 V rms maximum
Transient ANSI/IEEE C37.90.1-1989
Voltage Output Protection Continuous Short to Ground
Current Output Protection
130 V rms, continuous
Power Supply Voltages5
±15 V dc Supplies
   Rated Operation ±(13.5 V dc to 16.5 V dc)
   Current +50 mA, -15 mA
   Sensitivity ±0.01% span/V
+24 V dc Loop Supply
   Rated Operation +12 V dc to +30 V dc
   Current +27 mA @ lout = 20 mA
   Sensitivity ±0.0002% span/V
Mechanical Dimensions
3.15" x 3.395" x 0.775"
(80.0 mm x 86.2 mm x 19.7 mm)
Temperature Range
   Rated Performance -25°C to +85°C
   Storage -55°C to +85°C
Relative Humidity, 24 hours
0 to 95% @ +60°C noncondensing
RFI Susceptibility
±0.5% Span error @ 400 MHz, 5 Watt, 3 ft

1 For a 0 mA to 20 mA range, a typical minimum output current is 10 µA.
2 Includes the combined effects of repeatability, hysteresis, and nonlinearity.
3 With respect to the voltage output.
4 A wide range of custom zero suppression and span is available with the 3B18-00 model, using the AC1310 ranging card.
5 +24 V dc loop power is required for driving the current output at loads up to 850Ω. If a current output load of 400Ω or less is applied, +15 V dc is sufficient for loop power. If only voltage output is used, loop power is not required.

Specifications subject to change without notice.