Vaisala PTU300 - Manual (Page 107)

Chapter 4 _________________________________________________________________ Operation
VAISALA _______________________________________________________________________ 105
Limit RH Output Range
Use the serial line command RHLIMIT if you want to strictly limit the
allowed value of the relative humidity (RH) quantity to range 0 ... 100%.
The limit is implemented on all outputs and the display. Other quantities
are not affected, only RH. Note that seeing values above 100 %RH is
useful for detecting condensation on the sensor, and possible
measurement drift in very high humidities. For this reason, Vaisala
recommends leaving this feature at the default setting (off).
RHLIMIT [ON/OFF]
where
ON = Allowed range of RH output is 0 ... 100 %.
OFF = Allowed range of RH output is -5 ... 110 % (default).
Example (view current setting):
>rhlimit ?
RH limit 0...100: OFF
>
Example (enable RH limit):
>rhlimit on
RH limit 0...100: ON
>