3B47 ISOLATED, LINEARIZED, THERMOCOUPLE INPUT

Functional Description

The 3B47 is a single-channel isolated thermocouple signal-conditioning module which interfaces, amplifies, isolates, protects, linearizes and filters analog input voltages from a J, K, T, E, R, S or B-type thermocouple. The thermocouple input signal is internally linearized to provide an output voltage which is linear with temperature. 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. This plug-in, mix-and-match, hot-swappable module is easily field calibrated via front-panel zero and span adjustments.

Inside the 3B47 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). 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.

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.

Figure 1. 3B47 Functional Block Diagram

Figure 2. 3B47 Input Field Connection

Input Types Thermocouple Types: J, K, T, E, R, S, B Output Range 0 to +10 V

3B47 Models Available

¹The CJC sensor accuracy (refer to specification table) should be added to the module accuracy when computing system accuracy.
* Custom Input/Output ranges are available. Refer to configuration guide.

3B47 Specifications
(typical @ +25°C and ±15 V dc, and +24 V dc Power)

¹ Current output is not available with model 3B47.
² Includes the combined effects of repeatability, hysteresis, and nonlinearity.
³ A wide range of zero suppression and span adjustment is available to enable field calibration.
⁴ When used with the CJC temperature sensor provided on the 3B Series backplane. Specifications subject to change without notice.