The recommended PCB layout for the MAX31855CWP involves keeping the thermocouple traces as short as possible, using a dedicated ground plane, and avoiding running digital signals near the thermocouple inputs. A 4-layer PCB with a dedicated analog ground plane is recommended. Maxim provides a reference layout in the datasheet.
The MAX31855CWP has an internal cold junction compensation (CJC) circuit that measures the temperature of the IC and adjusts the thermocouple reading accordingly. However, for high-accuracy applications, it is recommended to use an external CJC sensor, such as a thermistor or a thermocouple, connected to the CJC pin. This provides a more accurate measurement of the cold junction temperature.
The maximum cable length for the thermocouple inputs depends on the type of thermocouple and the noise environment. As a general rule, shorter cables are recommended to minimize noise pickup. For most applications, cable lengths up to 10 feet (3 meters) are acceptable. However, for high-noise environments or longer cable lengths, it is recommended to use twisted-pair or shielded cables and to follow proper noise-reduction techniques.
Calibration of the MAX31855CWP involves adjusting the internal gain and offset registers to compensate for any errors in the thermocouple measurement. This can be done using a calibration routine that measures the thermocouple voltage at multiple temperatures and adjusts the registers accordingly. Maxim provides a calibration routine in the datasheet and also offers a calibration tool in their software development kit.
Noise can significantly affect the accuracy of the MAX31855CWP's thermocouple measurement. Electromagnetic interference (EMI), radio-frequency interference (RFI), and other types of noise can cause errors in the measurement. To minimize the effect of noise, it is recommended to use proper noise-reduction techniques, such as shielding, grounding, and filtering, and to follow proper PCB layout and design practices.
MAX3185CWP datasheet
by Maxim Integrated Products
