EC meter
From Wikipedia, the free encyclopedia
An EC meter (abbreviation of Electrical Conductivity meter) measures the electrical conductivity in a solution. Commonly used in hydroponics, aquaculture and freshwater systems to monitor the amount of nutrients, salts or impurities in the water.
[edit] Temperature dependence
The conductivity of a solution is highly 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.
Over a limited temperature range, the way temperature affect conductivity can be modeled linearly using the following formula:
![\sigma_T = {\sigma_{T_{cal}} [1 + \alpha (T - T_{cal})] }](../../../../math/5/d/1/5d1c6a77617c0d016baa52d374e8f005.png)
where
- T is the temperature of the sample,
- Tcal is the calibration temperature,
- σT is the electrical conductivity at the temperature T,
- σTcal is the electrical conductivity at the calibration temperature Tcal,
- α is the temperature compensation slope of the solution.
The temperature compensation slope for most naturally occurring waters is about 2 %/°C, however it can range between 1 to 3 %/°C. The compensation slope for some common water solutions are listed in the table below.
| Solution at 25 °C | Concentration (mass percentage) | α (%/°C) |
|---|---|---|
| HCl(aq) | 10 wt% | 1.56 |
| KCl(aq) | 10 wt% | 1.88 |
| H2SO4(aq) | 50 wt% | 1.93 |
| NaCl(aq) | 10 wt% | 2.14 |
| HF(aq) | 1.5 wt% | 7.20 |
| HNO3(aq) | 31 wt% | 31 |
