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Instruction for Use | HCA 56x and 8x8
5.5.3 Measuring of the Radiator and Ambiant Temperature
The following measurements are carried out during one cycle:
1. Measuring of the reference resistance Rref
2. Measuring of the ambient temperature sensor NTCA
3. Measuring of the radiator temperature sensor NTCR
The measuring values are calculated with the following formula:
The reference resistance value is defined ex works with a tolerance of 0.5% with 50 ppm. The
reference resistance features an excellent temperature and long-term stability.
The capacitor value and the threshold voltage have to remain stable over the whole cycle. How-
ever, they can vary at the medium- or long term without causing any failures because the self-cal-
ibration of the converter is repeated in every cycle while measuring the reference resistance.
ref
ref
NTC
Rref
ref
NTC
A
R
t
t
NTCR
t
t
NTC
RA
⋅=⋅=
5.6 Calculation of the displayed Consumption Value
The value displayed on the heat cost allocator is calculated as follows:
Single Sensor Device Dual Sensor Device
Explanation:
TH Temperature of the radiator surface in [°C]
TA Ambient temperature in [°C]
Q Displayed consumption value, without unit
Kc FactorthatcarriesbacktheΔTmeasuredatanormalizedvalue
Kq Factor Kq is a numerical value of the nominal power of the radiator stated in [KW]
Unit scale: Kc = 1 and Kq=1
Product scale: Kc <> 1 and Kq <> 1
5.5.2 Calculation of the Value of an Unknow Resistance (e.g Sensor Resistance)
The capacitor C is loaded at constant current. The interrupt at the end of the discharge is trig-
gered by the same threshold voltage (a fraction of the discharge voltage). If these two conditions
are met, the discharge time is directly proportional to the resistance. With a reference resistance
Rref whose exact value is known, it is now possible to calculate the unknown resistance value
Rx with the following equation:
From this equation the self-calibration of the converter can be derived, which is given by
measuring the discharging time through the reference resistance.
t
R
t
R
R
t
t
R
ref
ref
X
X
X
X
ref
ref
= ⇒ = ⋅
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