3B34 Isolated, Linearized RTD Input

The 3B34 is a single-channel signal conditioning module which amplifies, protects, filters, linearizes and isolates analog input voltages from a wide variety of two-, three- and four-wire Resistor Temperature Detectors (RTDs), providing simultaneous precision voltage and current outputs, linear to input temperature. RTD excitation current and three-wire lead resistance compensation provide a complete signal conditioning solution. The 3B34 protects its computer side outputs from damage and loss of signal integrity by isolating them up to ±1500 V peak and shielding its input and excitation circuit from damage from field-side overvoltage faults up to 220 V rms. The current output withstands 130 V rms without damage and interfaces to user equipment through screw terminals on the 3B Series backplane. The 3B34 is a plug-in, mix-and-match, hot-swappable module, easily field calibrated via front-panel zero and span adjustments for both voltage and current outputs.

3B Series Custom-Ranging Program

Externally-programmable version Model 3B34-00, 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 3B34 Module

A differential chopper-stabilized low-drift input amplifier provides stable gain and long-term stability. This enables the use of very low RTD excitation current to minimize self-heating and preserve measurement accuracy. A 250 µA excitation current for platinum and nickel RTDs and a 1 mA excitation current for copper RTDs is provided to create an input voltage to the 3B34. For three-wire RTDs, the excitation current flows through the third RTD lead to eliminate the effect of lead resistance with an accuracy of ±0.02°C/Ω. Internal multi-pole lowpass filtering with a 3-Hz cutoff (-3dB) enhances normal-mode and common-mode ejection at 50/60 Hz, enabling accurate measurement of small signals in high electrical noise. The differential input circuit on the field side is fully floating, eliminating the need for any input grounding. Signal isolation is accomplished by transformer coupling using a proprietary modulation technique for linear, stable and reliable performance. 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 voltage; this output also drives a voltage-to-current (V/I) converter to provide a simultaneous current output for interfacing versatility.

Figure 1. 3B34 Functional Block Diagram

Figure 2. 3B34 Input Field Connections

Input Type	Dual Outputs
100 Ω Platinum RTDs	0 to +10 V
10 Ω Copper RTDs	4 to 20 mA or 0 to 20 mA
120 Ω Nickel RTDs

	Model	RTD Sensor (2-, 3-, or 4-wire)	Input Range	Output  Ranges1
Order Now	3B34-00	100 Ω Pt, (alpha) = 0.00385	Externally Programmable2	0 V to +10 V & 0 mA to 20 mA
Order Now	3B34-01	100 Ω Pt, (alpha) = 0.00385	-100°C to +100°C	0 V to +10 V & 0 mA to 20 mA
Order Now	3B34-02	100 Ω Pt, (alpha) = 0.00385	0°C to +100°C	0 V to +10 V & 0 mA to 20 mA
Order Now	3B34-03	100 Ω Pt, (alpha) = 0.00385	0°C to +200°C	0 V to +10 V & 0 mA to 20 mA
Order Now	3B34-04	100 Ω Pt, (alpha) = 0.00385	0°C to +600°C	0 V to +10 V & 0 mA to 20 mA
	3B20-Custom	100 Ω Pt, (alpha) = 0.00385	*	*

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.

	Model	RTD Sensor (2- or 3-wire)	Input Range	Output  Ranges1
Order Now	3B34-C-00	10 Ω Copper, (alpha) = 0.004274	Externally Programmable2	0 V to +10 V & 0 mA to 20 mA
Order Now	3B34-C-01	10 Ω Copper, (alpha) = 0.004274	0°C to +120°C (10Ω @ 0°C)	0 V to +10 V & 0 mA to 20 mA
Order Now	3B34-C-02	10 Ω Copper, (alpha) = 0.004274	0°C to +120°C (10Ω @ +25°C)	0 V to +10 V & 0 mA to 20 mA
	3B34-Custom	10 Ω Copper, (alpha) = 0.004274	*	*

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

Description	Model 3B34
Input Range
Standard Ranges	Refer to Model Table
Custom Ranges	-200°C to +850°C (100Ω Platinum; 2-, 3- or 4-wire) -80°C to +350°C (120Ω Nickel; 2-, 3- or 4-wire) -100°C to +260°C (10Ω Copper; 2- or 3-wire)
Output Range
Voltage	0 V to +10 V (RL > 2 kΩ)
Current	4 mA to 20 mA or 0 mA to 20 mA (RL = 0 to 850Ω)1
Maximum Current Output Span	0 mA to 31 mA
Accuracy2
Initial @ +25°C	±0.1% Span
Nonlinearity3	±0.05% Span
Stability vs. Temperature
Voltage Output
Zero	±0.02°C/°C
Span	±25 ppm of Reading/°C
Current Output4
Zero	±25 ppm of Span/°C
Span	±25 ppm of Reading/°C
Zero and Span Adjustment Range5	±5% of Span
Input Bias Current	+3 nA
Input Resistance	15 MΩ
Noise
Input, 0.1 Hz to 10 Hz Bandwidth	0.2 µV rms
Output, 100 kHz Bandwidth	50 µV rms
Bandwidth, -3 dB	3 Hz
Output Rise Time, 10% to 90% Span	200 ms
Common Mode Voltage (CMV)
Input-to-Output, Continuous	±1500 V peak, maximum
Transient	ANSI/IEEE C37.90.1-1989
Common Mode Rejection (CMR)
1 kΩ Source Imbalance, 50/60 Hz	160 dB
Normal Mode Rejection, 50/60 Hz	60 dB
Sensor Excitation Current
100 Ω Pt, 120 Ω Ni	0.25 mA
10 Ω Cu	1.0 mA
Lead Resistence Effect
100 Ω Pt, 120 Ω Ni	±0.02°C/Ω
10 Ω Cu	±0.2°C/Ω
Input Protection (Includes Excitation Curcuits)
Continuous	220 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 Voltages6
±15 V dc Supplies
Rated Operation	-25°C to +85°C
Current	±10 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)
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 Linearization conformity error is ±0.05%.
⁴ With respect to the voltage output.
⁵ A wide range of custom zero suppression and span is available with the 3B30-00 and 3B31-00 models, using the AC1310 ranging card.
⁶ +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.