The recommended PCB layout for the MAX31855EEUT-T 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 design and layout guidelines in their application notes.
The MAX31855EEUT-T 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's recommended to use an external CJC sensor, such as a thermistor or a thermocouple, connected to the CJC pin. This allows for more accurate temperature measurement and compensation.
The maximum cable length for the thermocouple inputs of the MAX31855EEUT-T depends on the type of thermocouple, cable quality, and noise environment. As a general rule, keep the cable length as short as possible (less than 10 feet) to minimize noise pickup and ensure accurate readings. For longer cable lengths, use shielded cables and consider adding noise filters or amplifiers.
The MAX31855EEUT-T has a built-in thermocouple type detection circuit, but for high-accuracy applications, calibration may be necessary. Calibration involves measuring the thermocouple voltage at multiple temperatures and adjusting the internal calibration coefficients. Maxim provides a calibration procedure in their application notes, and some evaluation boards may also have built-in calibration capabilities.
The power-on reset (POR) timing for the MAX31855EEUT-T is typically around 10ms to 20ms, depending on the power supply ramp-up time and the specific application. During this time, the device is in a reset state, and the outputs are in a high-impedance state. After the POR timing, the device is ready to operate and provide accurate temperature readings.
MAX3189EEUT-T datasheet
by Maxim Integrated Products
