Vaisala PTB330 - Manual (Page 96)

USER'S GUIDE____________________________________________________________________
94 __________________________________________________________________ M210855EN-D
1102-007
Figure 39 Relay Output Modes
Mode 4 is usually used if an alarm needs to be triggered when the
measured value exceeds a safe range. The relay is active when
measurement is in range, and is released if the value goes out of range
or a power outage occurs.
NOTE If the measurement of the selected quantity fails or the barometer
loses its power, the relay is released.