3B20 AC Strain Gage, Torque Transducer Input

The 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.

Figure 1. 3B20 Functional Block Diagram

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

	Model	Excitation Voltage	Excitation Frequency	Input Range	Sensitivity	Output  Ranges1
Order Now	3B20-00	Externally Programmable2	Externally Programmable2	Externally Programmable2	Externally Programmable2	-10 V to +10 V & 0 mA to 20 mA
Order Now	3B20-01	5 V rms	3 kHz	20 mV rms	2 mV rms/V	-10 V to +10 V & 0 mA to 20 mA
	3B20-Custom	*	*	*	*	*

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.

(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
Accuracy2
Initial @ +25°C	±0.1% Span
Nonlinearity2	±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
Voltage4	2 V rms to 10 V rms
Voltage, tolerance	±2.5%
Frequency4	1 kHz to 10 kHz, ±15%
Drive	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
Continuous	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)
Environmental
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.