3B20 AC Strain Gage, Torque Transducer Input


Model 3B20-01The 3B20 is a wideband single-channel signal-conditioning module which interfaces 4-arm AC bridge transducer signals ranging between 1.5 mV rms and 150 mV rms, providing simultaneous precision voltage and current outputs. In addition, the module provides an AC excitation voltage of 2 V rms to 10 V rms at frequencies between 1 kHz and 10 kHz. The module withstands 130 V rms at its current output terminals without damage, thereby shielding computer-side circuitry from field-side overvoltage conditions. The 3B20 is a plug-in, mix-and-match, hot-swappable module and 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 3B20-00, enables the user to configure a special input range, including tare weight suppression, 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 3B20 Series Module

The 3B20 input and AC bridge excitation output terminals are protected for up to 130 V rms. The excitation amplitude and frequency can be specified with the Model 3B20-CUSTOM or user configured with Model 3B20-00 and an optional plug-on Model AC1310 ranging card. Both the voltage and current outputs can be independently adjusted for a minimum of ±1 V for the zero and 25% of the span range with front-panel user-accessible potentiometers. In addition, phase shifts of up to 37.25° between excitation signal and the output signal from the strain gauge or torque transducer can be compensated via front-panel screw terminal adjustments.

Input and Output Ranges

3B20 Functional Block Diagram

Figure 1. 3B20 Functional Block Diagram

3B18 Input Field Connections

Figure 2. 3B20 Input Field Connections

Input Type
Dual Outputs
1.5 mV rms to 150 mV rms
-10 V to +10 V
Full 4-Arm AC Strain Gage
4 mA to 20 mA or 0 to 20 mA
AC Torque Transducer

3B20 Models Available

Model  Excitation
Input Range Sensitivity Output 
Order Now 3B20-00
-10 V to +10 V &
0 mA to 20 mA
Order Now
5 V rms
3 kHz
20 mV rms
2 mV rms/V -10 V to +10 V &
0 mA to 20 mA

* *

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.

3B20 Specifications

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

Description  Model 3B20
Input Range
Standard Range
Refer to Model Table
Custom Ranges
Vin = 1.5 mV rms to 150 mV rms
Vexc = 2 V rms to 10 V rms
Vexc freq. = 1 kHz to 10 kHz
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
   With Input Overload
40 mA, maximum
Initial @ +25°C
±0.1% Span
±0.05% Span
Stability vs. Temperature
Voltage Output
   Zero ±0.005% of Span/°C
   Span ±0.01% of Span/°C
Current Output3
   Zero ±25 ppm of Span/°C
   Span ±25 ppm of Reading/°C
Bridge Excitation
2 V rms to 10 V rms
Voltage, tolerance
Frequency4 1 kHz to 10 kHz, ±15%
Up to 20 mA rms, minimum
Harmonic Distortion
< 0.5%
Span Calibration Adjustment Range4
±25% of span, minimum
Zero Calibration Adjustment Range4
±1 V, minimum
Phase Adjustment Range5
0 to 4.25° minimum @ 1 kHz
0 to 14° minimum @ 3.28 kHz
0 to 37.25° minimum @ 10 kHz
Input Bias Current
+10 nA
Input Resistance
100 MΩ
Bandwidth, -3 dB
100 Hz
Output Rise Time, 10% to 90% Span
200 ms
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 V dc to 18 V dc)
   Current ±65 mA
   Sensitivity ±0.03% span/V
+24 V dc Loop Supply
   Rated Operation +13.5 V dc to +30 V dc
   Current +27 mA @ lout = 20 mA
   Sensitivity ±0.001% 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 3B20-00 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.