User Manual

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Siemens Frost detectors A6V10432020_en--_c
2019-04-29
Use
On the air side of ventilation and air conditioning plants:
 Typically: hot water air heating coils where there is a risk of freezing due to cold
incoming outside air
 Where fans are to be switched off, heating valves opened, air dampers closed or
other actions need to be taken by the control system to prevent freeze-ups
Functions
With the help of a vapor-filled capillary tube and diaphragm, the QAF63.. acquires
the lowest temperature which occurs along at least 250 mm length of capillary tub-
ing.
If the frost detector is correctly located at the air outlet of the air heating coil, it ac-
quires the lowest air temperature even in the case of temperature stratification. The
vapor pressure in the capillary tube produces a certain diaphragm travel. This
movement is converted to an electric signal with the help of an inductive measuring
system. It is then electronically amplified so that a DC 0…10 V measuring signal
can be produced (terminal B).
To make certain it is always the lowest temperature along the capillary tube that is
acquired, the temperate of the diaphragm inside the housing must always be high-
er than the temperature at the capillary tube. This is ensured by a heating element
inside the housing, which maintains the temperature at the diaphragm above 15 °C
as long as the ambient temperature does not fall below -15 °C.
Mechanical design
The frost detector consists of a two-sectional housing (base and cover) and a capil-
lary tube which is active over its full length.
The cover is secured to the base with a fixing screw and can be removed.
The housing accommodates the electronics, the diaphragm with the heating ele-
ment, the connection terminals and the type field.
Connection terminals and type field can be accessed after removing the cover.
The cables are introduced to the housing from below. There is one hole for the en-
closed cable gland M16, and 2 knockout holes for additional cable glands M16.
The QFA63... can be fitted directly to the wall – with or without a test loop – or with
the help of a mounting flange (if the air duct is insulated).
Technical design