2B56 Datasheet, PDF (1/1 Pages) List of Unclassifed Manufacturers – High Accuracy, Thermocouple Cold Junction Compensator

High Accuracy, Thermocouple
Cold Junction Compensator
Model 2B56
FEATURES
Universal Thermocouple Compensation:
Internally Provided: Types J, K, T
User Configurable: Types E, R, S, B
Digitally Programmable Type Select
High Accuracy: ±0.8°C max over +5°C to +45°C
High Ambient Rejection: 50 to 1 min.
Low Cost
Small Size: 1.5" X 2" X 0.4"
APPLICATIONS
Thermocouple Signal Conditioning
Temperature Measurement and Control Systems
Temperature Data Acquisition and Logging
Temperature Controllers
GENERAL DESCRIPTION
Model 2B56 is a high accuracy, universal thermocouple cold junction
compensator. Designed to operate with an external temperature sensor
in thermal contact with the cold junction, the 2B56 provides an
automatic compensation for amplified thermocouple signals over wide
ambient temperature variations. The 2B56 is calibrated to compensate
the cold junction to a reference temperature of 0°C. The total
compensation error is ±0.8°C max over +5°C to +45°C.
Designed to compensate seven different thermocouple types, the 2B56
may be digitally programmed to select compensation for types J, K
and T, and one user programmed type (E, R, S, B or none). This
feature makes the 2B56 especially suitable for multichannel
applications involving several thermocouple types.
COLD JUNCTION COMPENSATION PRINCIPLES
In thermocouple measurements, temperature is determined by
measuring the potential difference between the measurement (hot)
junction of two dissimilar metals and the reference (cold) junction
which is formed when thermocouple leads are connected to a
measuring circuit. Since this potential difference is proportional to the
temperature difference between the measurement temperature and the
temperature at the reference junction, the reference junction
temperature must be known. Changes in reference junction
temperature influence the output voltage and, therefore, cold junction
compensation is required to eliminate measurement errors.
Two methods may be used to reduce errors introduced at the
thermocouple connections: keep the reference junction at a known
constant temperature, or measure the reference junction temperature
and cancel the changes by the appropriate correction
Information furnished by Intronics is believed to be accurate and reliable. However, no
responsibility is assumed by Intronics for its use; nor for any infringements of patents or
other rights of third parties which may result from its use. No license is granted by
implication or otherwise under any patent or patent rights of Intronics.
to the thermocouple output signal. The first method, accomplished by
immersing the reference junction in an ice bath maintained at 0°C is
not very practical. The 2B56 employs the second method and has been
specifically designed to eliminate the need for ice baths by
electronically simulating the desired reference point. Digital
programmability, high accuracy and low cost make the 2B56 ideal for
single or multichannel thermocouple temperature measurement,
indication or control systems.
FUNCTIONAL DESCRIPTION
The 2B56 compensates for cold junction temperature by adding a
correction signal at the output of the user's thermocouple amplifier, as
shown in Figure 1. The value of the correction signal is determined by
the cold junction temperature, as measured by a sensor, and the
thermocouple type in use, as specified by two digital TYPE SELECT
inputs. Since compensation is done at the output of the thermocouple
amplifier it is also necessary to scale the correction signal for the gain
of the amplifier. This is done by a scaling circuit which has provision
for a user-supplied gain-setting resistor for each thermocouple type in
use.
Compensating networks for thermocouple types J, K, and T are
built into the 2B56. A fourth compensation (X) can be
programmed with two external resistors for any other
thermocouple type. The X compensation can also be used without
programming resistors to obtain an uncompensated output when
sensors other than thermocouples are in use.
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