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# EC meter

An EC meter measures the electrical conductivity in a solution. Commonly used in hydroponics and aquaculture systems to monitor the amount of nutrients / salt in the water.

## Temperature dependence

The conductivity of a solution is temperature dependent, therefore it is important to either use a temperature compensated instrument, or calibrate the instrument at the same temperature as the solution that you want to measure.

The way temperature affect conductivity can be modeled using the following formula:

$\sigma_T = {\sigma_{T_{cal}} [1 + \alpha (T - T_{cal})] }$

where

σT is the electrical conductivity at the measured temperature, T
σTcal is the electrical conductivity at a common temperature, Tcal
T is the measured absolute temperature in kelvin,
α is the temperature compensation slope of the material,
Tcal is the common temperature in kelvin.

The temperatures should be specified in kelvin, (or degree Celsius).

α for some common materials are listed in the table below.

Substance at 25°C Concentration (weight percent) α
HCl 10 wt% 1.56
KCl 10 wt% 1.88
H2SO4 50 wt% 1.93
NaCl 10 wt% 2.14
HF 1.5 wt% 7.20
HNO3 31 wt% 31.0