Datasheet

Applications Information
Noise Considerations
Because of the small signal levels involved, thermocouple
temperature measurement is susceptible to powersupply
coupled noise. The effects of power-supply noise can be
minimized by placing a 0.1µF ceramic bypass capacitor
close to the V
CC
pin of the device and to GND.
The input amplifier is a low-noise amplifier designed
to enable high-precision input sensing. Keep the ther-
mocouple and connecting wires away from electrical
noise sources. It is strongly recommended to add a
10nF ceramic surface-mount differential capacitor, placed
across the T+ and T- pins, in order to filter noise on the
thermocouple lines.
Thermal Considerations
Self-heating degrades the device’s temperature measure-
ment accuracy in some applications. The magnitude of
the temperature errors depends on the thermal conduc-
tivity of the device package, the mounting technique, and
the effects of airflow. Use a large ground plane to improve
the device’s temperature measurement accuracy.
The thermocouple system’s accuracy can also be
improved by following these precautions:
• Use the largest wire possible that does not shunt heat
away from the measurement area.
• If a small wire is required, use it only in the region
of the measurement, and use extension wire for the
region with no temperature gradient.
• Avoid mechanical stress and vibration, which could
strain the wires.
• When using long thermocouple wires, use a twisted
pair extension wire.
• Avoid steep temperature gradients.
• Try to use the thermocouple wire well within its tem-
perature rating.
• Use the proper sheathing material in hostile environ-
ments to protect the thermocouple wire.
• Use extension wire only at low temperatures and only
in regions of small gradients.
• Keep an event log and a continuous record of thermo-
couple resistance.
MAX31855 Cold-Junction Compensated
Thermocouple-to-Digital Converter
www.maximintegrated.com
Maxim Integrated │ 11