Measuring principle of HVAC temperature sensors in general:
The measuring principle of temperature sensors is based on an internal sensor that outputs a temperature-dependent resistance signal.
The type of the internal sensor determines the output signal. The following active ⁄ passive temperature sensors are distinguished:
a) Pt 100 measuring resistor (according to DIN EN 60 751)
b) Pt 1000 measuring resistor (according to DIN EN 60751)
c) Ni 1000 measuring resistor (according to DIN EN 43 760, TCR = 6180 ppm ⁄ K)
d) Ni 1000_TK 5000 measuring resistor (TCR = 5000 ppm ⁄ K)
e) LM235Z, semiconductor IC (10 mV ⁄ K, 2.73 V ⁄ °C). Ensure correct po ⁄– when connecting!
f) NTC (according to DIN 44070)
g) PTC
h) KTY silicon temperature sensors
The most important resistance characteristics are shown on the last page of these operating instructions. According to their characteristics,
individual temperature sensors exhibit different slopes in the range between 0 °C and +100 °C (TK value). Maximum-possible measuring ranges
also vary from sensor to sensor (for some examples to this see under technical data).
Design of HVAC temperature sensors in general:
Sensors are distinguished by shape type as follows: surface-contacting sensors, cable temperature sensors, and housing-type and built-in
temperature sensors.
– On surface-contacting sensors, the temperature sensor has at least one contact area that must be brought in contact, e.g. with the surface of
radiators or pipes. If the contact area is not positioned correctly relative to the surface to be measured, significant temperature measurement
errors may occur. Good contact area and temperature conduction must be ensured, dirt and unevenness must be avoided, and heat-conductive
paste is to be used where necessary.
– On cable temperature sensors, the temperature sensor is installed inside a sensor sleeve, from which a connecting cable is leading out. In addition
to the standard insulating materials PVC, silicone, and fibreglass with stainless steel texture, other versions are also available that may allow a
wider range of application.
– On housing-type sensors, the temperature sensor is embedded in a respective housing. Different designs of housings are available, e.g. with an
external sensor sleeve (see outside temperature sensor ATF2). Housing-type sensors are normally distinguished into in-wall (FSTF) and on-wall
(RTF, ATF) types and indoor and wet room versions. Connection terminals are placed on a plate inside the connecting housing.
– Duct and built-in temperature sensors are distinguished into temperature sensors with interchangeable measuring insert and without
interchangeable measuring insert. Connection parts are placed inside a connecting head. Standard process connection for immersion sensors
is a pipe thread (sizes in inches) and a mounting flange for duct sensors. However, it may be designed differently. When a built-in sensor has a
neck tube, the application range is usually somewhat wider since ascending heat cannot flow directly and immediately into the connecting head.
This is to be noted especially when transmitters are installed. The temperature sensor in built-in sensors is always placed inside the front part
of the protective tube. On temperature sensors with short reaction times, protective tubes are stepped.
Note!
Select immersion depth for built-in sensors so that the error caused by heat dissipation stays within the admissible error margins. A standard value
is: 10 x diameter of protection tube + sensor length. In connection with housing-type sensors, particularly with outdoor sensors, please consider
the influence of thermal radiation. For that purpose, a sunshade and radiation protector SS-02 can be attached.
G
General notes
Component
............................................................ max. thermal load
Connecting cable
PVC, normal .............................................................................. +70 °C
PVC, heat-stabilized ................................................................ +105 °C
Silicone ................................................................................... +180 °C
PTFE .......................................................................................+200 °C
Fibreglass insulation with stainless steel texture ...................+400 °C
Housing ⁄ Sensor
see table "Technical Data"
Maximum thermal load on components:
On principle, all temperature sensors shall be protected
against unacceptable overheating!
Standard values for individual components and materials
selected are shown for operation under
neutral atmos phere and otherwise normal conditions
(see table to the right).
For combinations of different insulating materials,
the lowest temperature limit shall always apply.