The phrase "is valid only when" is grammatically correct and can be used in written English.
It is typically used to express a condition or requirement that must be met in order for something to be considered valid or true. Example: "The warranty is valid only when the product is purchased from an authorized retailer."
Inter-validation between satellite and SO2-flux derived TADR is valid only when the pre-eruptive sulfur content is constant.
This statement is valid only when the considered joint length is longer than the wavelengths of the incident waves.
Although the conventional shrinking core model (SCM) has been applied to such systems previously, its use is valid only when adsorption onto the pore walls is described by a rectangular isotherm.
Although the well-known harmonic vibration solution is valid only when the reciprocating motion is slow, this approximate solution is valid for a wide range of both motions, reciprocating and vibrating.
In the first method, the lower lags of the auto-covariance function are used to estimate the observed noise variance with high estimation accuracy, but it is valid only when the AR order is greater than the MA order.
This is valid only when the depth of the channels (C) is lower than the widths of the mixing (A) and inlet (B) channels i.e. when A/C and B/C are both greater than unity.
At foil, hits must be made with the point of the weapon and are valid only when they land on the prescribed target area (the trunk of the body).
However, the results established in [29] are valid only when the graininess function is bounded which is a restrictive condition.
Standard corrections for clustering are valid only when the number of groups or clusters is large (Wooldridge 2003).
However, this intuitive extension is found to be valid only when the speed deviations for all other generators are zeros, while it is not tenable in general [30].
In such kind of application scenarios, sensory data are valid only when they reach the sink within the specified time threshold.
