Hach-Lange 3798-S sc - Manual (Page 8)

6
General information
This temperature-dependence, expressed in [% / °C], is termed the temperature
coefficient (
α).
C
Tref
= C
T
[1 + α (T – T
ref
)] – 1
2.4 Measuring principle
The tip of the probe comprises two coils that are completely insulated from the
surrounding medium.
The electrical insulation between liquid and sensor (magnetic coupling) has
advantages compared to the conventional method of using metal electrodes:
• no polarisation, for this reason the measuring range is larger
• high mechanical and chemical resistance
• possibility of taking measurements in soiled liquids
C
Tref
: conductivity adjusted to the reference temperature
C
T
: conductivity measured at T
T
ref
: reference temperature (as a rule 25 °C)
α : coefficient of the liquid temperature ( % /
°C
)
Primary coil
(transmitter): An AC voltage is applied to the primary coil and produces an
alternating electromagnetic field in the surrounding liquid. This
magnetic field generates an electrical current in the liquid.
Secondary coil
(receiver): The secondary coil determines the current produced by the
ion movements and calculates the conductivity of the liquid
from the current.
1. Receiver
2. Oscillator
3. Cable
4. Insulation
5. Receiver coil
6. Transmitter coil
7. Field line
1
4
5
2
3
6
7