3B34 ISOLATED,LINEARIZED RTD INPUT

Functional Description

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

3B34 Models Available

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.

3B34 Specifications
(typical @ +25°C and ±15 V dc, and +24 V dc Power)

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.
Specifications subject to change without notice.