Rev. 0.2 / 09 /2015
8
AN1111-2
3 RH measurement with pre-adjusted HCT01 and
microcontroller based, initially accurate circuitry
A measuring device with pre-adjusted HCT01 and with a microcontroller based initially accurate
circuitry can achieve an accuracy of ±2,24 % rH.
A detailed description of the circuitry is available in the E+E patent EP 1 574 847 B1 // US 7,084,644
B2.
3.1 Schematic circuit diagram
Figure 6: Schematic circuit design
1
There are three possible measurement paths:
1.)
Sensor
(capacitance) path with
R1 + HCT01 + D1 + C2 (= C
L
)
2.)
Reference
(capacitance) path with R2 + C_REF + D1 + C2 (= C
L
)
3.)
Calibration
(capacitance) path with R3 + C_CAL + D1 + C2 (= C
L
)
U
L
= voltage at C
L
(=C2)
U
V
= Voltage at the voltage
divider (reference voltage)
1
C_REF = ±1%
@82 pF = ±0.82 pF ≈ ±3.4 % rH
C_Cal= Capacitance which is used for calibration end testing [no soldering necessary]
