Emerson Mobrey Hydratect 2462, Reference Manual

Page: 13 / 66

7
Reference Manual
24625020, Rev AA
Introduction
March 2017
Introduction
1.6 How electrodes operate
1.6.1 Conductivity and resistance values of steam and water
Figure 1-5 shows conductivity and resistance values of steam, pure water, and typical boiler
water. The significant difference between the resistance of steam and boiler water allows
the Hydratect 2462 system to differentiate between the two.
An electrode acts as a resistor when inserted into the pipe containing the steam or water.
Resistance values are greater than 10 M

for steam and between 2 k

and 100 k

for boiler
water. In a Hydratect 2462 Electronics Control Unit, the resistance forms the lower half of a
potential divider, across which an alternating driving signal is applied. The signal amplitude
of the potential divider output is high for steam (~±6 V) and low for water (~±3 V).
Two conductivity values, 0.6

S/cm for high sensitivity and 1.6

S/cm for low sensitivity, are
selectable to suit the operating conditions and the purity of the boiler water.
See
“Setting the printed circuit board (PCB) jumpers” on page 23 for further information.
Figure 1-5. Conductivity and Resistance of Steam and Water
A. Typical steam values. D. Typical boiler water
B. Hydratect switching band (0.6

S/cm setting). E. Pure water.
C. Hydratect switching band (1.6

S/cm setting).
A
B
C
D
E
Temperature (°C)
200 300 400
0.01
0.1
1
10
100
1
10
100
1000
10000
Co
nd
uc
ti
vi
ty (

S/cm)
Resistance (K

)