Data Sheet for Product

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Siemens Frost detector A6V10432022_en--_e
Smart Infrastructure 2021-04-20
Functions
With the help of a vapor-filled capillary tube and diaphragm, the QAF64… acquires
the lowest temperature which occurs along at least 250 mm length of capillary tub-
ing.
When correctly located at the air outlet of the air heating coil, the frost detector ac-
quires the lowest air temperature even in the case of temperature stratification. The
vapor pressure in the capillary tube produces a certain travel of the diaphragm.
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 measur-
ing signal can be produced (terminal B).
The frost detector performs its task by providing 3 independent functions:
1. It opens the heating valve continuously within a proportional control range.
2. It switches off the fans and closes the air dampers via its relay contact.
3. It makes the acquired temperature available for further handling.
The measuring signal is then used as a frost signal by the frost detector and for
valve control. The frost signal starts rising at about 6 K above the adjusted frost
value.
P Frost value (adjustable)
T Capillary tube temperature
Y10 Valve control signal (at Y = DC 0 V)
Q11/12/13 Relay output (changeover contact)
The frost signal is added to the valve control signal fed to signal input Y. This
causes the heating valve to travel to its fully open position – resulting from the con-
trol signal received via signal output Y10 – before the output relay changes to the
"Frost" position (Q11-Q12). This circuitry prevents frequent switching of the plant
during the startup phase.
To make certain it is always the lowest temperature along the capillary tube that is
acquired, the temperature of the diaphragm inside the housing must always be
higher than the temperature at the capillary tube. This is ensured by a heating ele-
ment 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.
Technical design
Function diagram
Legend
Startup function