EC Meters,
nutrient labels and general literature represent conductivity values in
several ways. The more common representations (or ‘units’) are:
+
mS/cm (often abbreviated as “mS”). Pronounced “milli-siemens per
centimeter”.
+ µS/cm
(often abbreviated as “µS”).
Pronounced “micro-siemens per centimeter”.
+
cF (conductivity factor).
+
ppm* (parts per million) or mg/L (milligrams per litre). These both have the same
numeric value. These are the units for “total dissolved salts” (TDS).
Meters that provide these units have internal software that mathematically
converts conductivity readings into a TDS estimate. However, as discussed in later sections, this estimate is prone to many errors
and therefore its use should be avoided.
To utilize conductivity recommendations (e.g. from a nutrient label –
Fig 2.3), you must first know what ‘units’ (e.g. mS/cm, cF) your meter
operates in. This will be displayed on either the digital display or
stamped on the body of the meter. Some brands offer multiple options
e.g. cF, mS and uS. If this is the case, choose the option that
matches that used on the nutrient label – or the recommendation you were
given. For example, if a nutrient label specifies “mS” then switch the
meter to read “mS”.
If your meter is incapable of producing units that match the conductivity
recommendation, then manually convert the values to match (see Table 2.20a).
For example, if the label gives a recommendation of 2.0mS but your meter
only works in cF, then convert the recommendation to cF by multiplying it by
10. i.e. 2.0mS x 10 = cF 20.
