3B37 Isolated, Thermocouple Input


Model 3B37-K-02The 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.

Input and Output Ranges

3B37 Functional Block Diagram
Figure 1. 3B37 Functional Block Diagram

3B37 Input Field Connections
Figure 2. 3B37 Input Field Connections

Input Type
Dual Outputs
Thermocouples: J, K, T, E, R, S, B
0 to +10 V or -10 V to +10 V

0 to 20 mA or 4 to 20 mA

3B37 Models Available

Model  Input Type Input Range Output 
Order Now 3B37-X-00
Type J, K, T, E, R, S, or B Externally Programmable2
0 V to +10 V & 0 mA to 20 mA
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Type J -100°C to +100°C (-148°F to +1400°F)
0 V to +10 V & 0 mA to 20 mA
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3B37-K-02 Type K
-100°C to +1350°C (-148°F to +2462°F)
0 V to +10 V & 0 mA to 20 mA
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 Type T -100°C to +400°C (-148°F to +752°F)
0 V to +10 V & 0 mA to 20 mA
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Type E
0°C to +900°C (+32°F to +1652°F)
0 V to +10 V & 0 mA to 20 mA
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Type R
0°C to +1750°C (+32°F to +3182°F)
0 V to +10 V & 0 mA to 20 mA
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Type S
0°C to +1750°C (+32°F to +3182°F)
0 V to +10 V & 0 mA to 20 mA
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Type B
0°C to +1800°C (+32°F to +3272°F)
0 V to +10 V & 0 mA to 20 mA

Type J, K, T, E, R, S, or B
* *

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)

Description  Model 3B37
Input Range
Standard Ranges
Refer to Model Table
Custom Ranges
±5 mV to ±500 mV
Output Range
Voltage (RL > 2K)
0 V to +10 V; -10 V to +10 V
Current (RL = 0 to 850Ω)1
4 mA to 20 mA or 0 mA to 20 mA
   Maximum Current Output Span
0 mA to 31 mA
Initial @ +25°C
±0.1% Span + CJC Sensor Error
±0.01% 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 Range4 ±5% of Span
Cold Junction Compensation (CJC)5
Initial Accuracy @ +25°C
±0.5 °C
Accuracy vs. Temperature, +5°C to +45°C
±0.5°C (±0.0125°C/°C)
Input Bias Current +15 nA
Input Resistance
15 MΩ
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
Open Input Response
Open Input Detection Time 10 seconds
Common Mode Voltage (CMV)
Input-to-Output, Continuous
±1500 V peak, maximum
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
Input Protection
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 ±(11.5 V dc to 16.5 V dc)
   Current ±12 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)
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 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.