3B37 ISOLATED, THERMOCOUPLE INPUT

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Functional Description

The 3B37 is a single-channel signal conditioning module that interfaces, amplifies and filters input voltages from a J, K, T, E, R, S or B-type thermocouple and provides isolated simultaneous voltage and current outputs linear with input voltage. High accuracy internal cold junction compensation and a predictable upscale open circuit indication provide a complete signal conditioning solution. To accurately measure low level signals in electrically noisy environments, ±1500 V peak of galvanic transformer-based isolation with a common mode rejection (CMR) of 160 dB @ 50/60 Hz and a normal mode rejection (NMR) of 60 dB @ 50/60 Hz are provided. The current output withstands 130 V rms without damage and interfaces user equipment through screw terminals located on the 3B Series backplane. This plug-in, mix-and-match, hot-swappable module is easily field calibrated via front-panel zero and span adjustments for both voltage and current outputs.

Accurate and System-Ready

Internal cold-junction compensation largely corrects errors arising from parasitic thermocouples formed by thermocouple connection to the input screw terminals, providing an accuracy of ±0.5°C over the +5°C to + 45°C ambient temperature range. The module generates a predictable upscale signal to indicate an open thermocouple; for a downscale response, connect a 47 MΩ, 0.25 Watt resistor across screw terminals 2 and 4 on the 3B Series backplane.

3B Series Custom-Ranging Program

Externally-programmable version Model 3B37-X--00, enable 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 3B37 Module

A chopper-stabilized low-drift input amplifier assures stable long-term stability. At the amplifier input, a zero-scale input voltage is subtracted from the input signal to set the zero-scale value. For user convenience, the zero and span optionally can be factory configured to meet custom needs (Model 3B37-CUSTOM) or can be externally programmed (Model 3B37-X-00) via user-supplied resistors inserted in the optional AC1310 plug-on ranging card. Zero suppression can exceed 100% of the input range. This enables suppression of a zero-scale input value many times larger than the total span for precise expanded-scale measurements of a selection portion of an input signal. The differential input circuit on the field side is fully floating, eliminating the need for any input grounding. Signal isolation by transformer coupling uses 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. 3B37 Functional Block Diagram

Figure 2. 3B37 Input Field Connections

3B37 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.

3B37 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 With respect to the voltage output.
⁴ A wide range of custom zero suppression and span is available with the 3B30-00 and 3B31-00 models, using the AC1310 ranging card.
⁵ When used with the CJC temperature sensor provided on the 3B Series backplane.
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.