Chapter Three: Overview Tri
Point Value
19
Trip Point Value
The trip point pressure is designated at the time the unit is ordered and
cannot
be changed in the
field.
Caution
The trip point value is NOT ADJUSTABLE. Before operating the
switch, ensure that the range of pressure for the system is
appropriate for the particular 41/42/51/52 switch.
The trip point pressure value must be in the same pressure units as the full scale range. For
example, you cannot order a 1000 Torr full scale unit with a trip point of 14.7 psia; you must
specify the trip point as 760 Torr.
How The Full Scale Range Affects Trip Point Accuracy
The accuracy of the pressure switch (reacting to the trip point) depends on the full scale range of
the unit. Therefore, you should order the
lowest
full scale range switch that will measure the trip
point value. For example, if you need a trip point of 50 Torr, a 100 Torr full scale range will
provide a trip point accuracy of 0.5 Torr. The switch will trip between 49.5 and 50.5 Torr.
However, a 1000 Torr full scale switch with the same 50 Torr trip point will provide a trip point
accuracy of only 5 Torr. Therefore the switch will trip between 45 and 55 Torr.
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