M241 and M258 frequency meters have a "Validity" output which is FALSE when no pulses are received after the duration defined in "Time base" parameter ( 10, 100 or 1000 ms).
When "Validity" output is FALSE, "CurrentValue" has the last computed frequency value (not 0), but this value must be ignored.
When "Validity" output is FALSE, "CurrentValue" has the last computed frequency value (not 0), but this value must be ignored.