The MECA contains a Thermal and Electrical Conductivity Probe (TECP).
The TECP, designed by Decagon Devices, has four probes that made the following measurements: Martian soil temperature, relative humidity, thermal conductivity, electrical conductivity, dielectric permittivity, wind speed, and atmospheric temperature.

Three of the four probes have tiny heating elements and temperature sensors inside them.
One probe uses internal heating elements to send out a pulse of heat, recording the time the pulse is sent and monitoring the rate at which the heat is dissipated away from the probe.
Adjacent needles sense when the heat pulse arrives.
The speed that the heat travels away from the probe as well as the speed that it travels between probes allows scientists to measure thermal conductivity, specific heat (the ability of the regolith to conduct heat relative to its ability to store heat) and thermal diffusivity (the speed at which a thermal disturbance is propagated in the soil).

The probes also measured the dielectric permittivity and electrical conductivity, which can be used to calculate moisture and salinity of the regolith.
Needles 1 and 2 work in conjunction to measure salts in the regolith, heat the soil to measure thermal properties (thermal conductivity, specific heat and thermal diffusivity) of the regolith, and measure soil temperature.
Needles 3 and 4 measure liquid water in the regolith.
Needle 4 is a reference thermometer for needles 1 and 2.

The TECP humidity sensor is a relative humidity sensor, so it must be coupled with a temperature sensor in order to measure absolute humidity.
Both the relative humidity sensor and a temperature sensor are attached directly to the circuit board of the TECP and are, therefore, assumed to be at the same temperature.
The MECA contains a Thermal and Electrical Conductivity Probe (TECP). The TECP, designed by Decagon Devices, has four probes that made the following measurements: Martian soil temperature, relative humidity, thermal conductivity, electrical conductivity, dielectric permittivity, wind speed, and atmospheric temperature.
Three of the four probes have tiny heating elements and temperature sensors inside them. One probe uses internal heating elements to send out a pulse of heat, recording the time the pulse is sent and monitoring the rate at which the heat is dissipated away from the probe. Adjacent needles sense when the heat pulse arrives. The speed that the heat travels away from the probe as well as the speed that it travels between probes allows scientists to measure thermal conductivity, specific heat (the ability of the regolith to conduct heat relative to its ability to store heat) and thermal diffusivity (the speed at which a thermal disturbance is propagated in the soil).
The probes also measured the dielectric permittivity and electrical conductivity, which can be used to calculate moisture and salinity of the regolith. Needles 1 and 2 work in conjunction to measure salts in the regolith, heat the soil to measure thermal properties (thermal conductivity, specific heat and thermal diffusivity) of the regolith, and measure soil temperature. Needles 3 and 4 measure liquid water in the regolith. Needle 4 is a reference thermometer for needles 1 and 2.
The TECP humidity sensor is a relative humidity sensor, so it must be coupled with a temperature sensor in order to measure absolute humidity. Both the relative humidity sensor and a temperature sensor are attached directly to the circuit board of the TECP and are, therefore, assumed to be at the same temperature.
Phoenix (spacecraft)