Datasheet

�� Maxim Integrated Products 11

MAX31855

Cold-Junction Compensated

Thermocouple-to-Digital Converter

Applications Information

Noise Considerations

Because of the small signal levels involved, thermocou-

ple temperature measurement is susceptible to power-

supply coupled noise. The effects of power-supply noise

can be minimized by placing a 0.1FF ceramic bypass

capacitor close to the V

pin of the device and to GND.

The input amplifier is a low-noise amplifier designed to

enable high-precision input sensing. Keep the thermo-

couple 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 conductivity

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.