# ATC

> ATC (automatic temperature compensation) is a meter feature that corrects pH or EC readings for sample temperature, usually referencing EC to 25 °C.

- Canonical: https://genetixbay.com/knowledge/glossary/atc.html
- Also written: automatic temperature compensation, temperature compensation, temp compensation, temperature-compensated
- Glossary category: pH, EC and water · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

ATC (automatic temperature compensation) uses a built-in temperature sensor to correct readings. It works differently for [EC](https://genetixbay.com/knowledge/glossary/ec.md) and [pH](https://genetixbay.com/knowledge/glossary/ph.md), and growers often misunderstand the pH part.

## In practice

**EC:** conductivity rises roughly 2% per °C. An uncompensated reading of a 1.40 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md) solution would read about 1.54 at 30 °C and 1.26 at 20 °C. With ATC, the meter converts readings to the 25 °C reference so numbers are comparable. This matters a lot for EC; without ATC, cold reservoirs look weak and warm ones look strong.

**pH:** ATC corrects for how the electrode's response (its slope, about 59 mV per pH unit at 25 °C) changes with temperature. It does not correct for the real pH change of the solution itself with temperature, which is small for nutrient solutions. So a compensated [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) reports the true pH at the sample's current temperature.

Best practice: let probe and sample reach the same temperature, and calibrate near the temperature you measure at. Large gaps (cold reservoir, warm buffer) still cause errors and slow readings.

## Units and formula

EC₂₅ ≈ EC_T ÷ (1 + 0.02 × (T − 25)), T in °C. Some meters let you set the coefficient (1.9–2.1% per °C).

## Don't confuse with

- **Calibration**: corrects the electrode against standards; ATC corrects for temperature.

## Related terms

[EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md), [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md), [EC](https://genetixbay.com/knowledge/glossary/ec.md), [Two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md)

## Read more

- [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)
- [EC vs PPM: the 500 and 700 scales, CF, and how to convert](https://genetixbay.com/knowledge/ph-ec/ec-ppm-scales.md)

## Sources

1. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test-water-quality