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Hydrastep 2468CB and 2468CD Manual Introduction to the Hydrastep 2468 Electronic Gauging System
24685034
1-3
1.1 WATER LEVEL MEASUREMENT
The Hydrastep 2468 Electronic Gauging System is designed as an electronic alternative to
water level gauges on boilers, giving a more reliable and safer water level indication than
conventional visual gauges. It uses the significant difference in resistivities of water and
steam in temperatures up to 370C (698F) to determine the water level.
Figure 1.2 - Schematic of resistance measuring cell and electrodes
A vertical row of electrodes is installed in the water level column attached to boiler and
typically aligned so that half the electrodes are above and half below the normal water level
(see Figure 1.2). The resistance measurement is made between the insulated tip of each
electrode and the wall of the column.
The “cell constant” defining the actual resistance measured is determined by the length and
diameter of the electrode tip and the column bore. In practice, the cell constant is chosen so
that the resistance in water is less than 100k ohms and the steam resistance is greater than
10M ohms. Since the resistivities of water and steam are substantially different, the system
is simple and requires no setting up adjustments. It is not susceptible to power supply
variations, ambient temperature changes, etc., resulting in a highly reliable system.
A general overview showing how a typical Hydrastep 2468 System is installed is illustrated
in Figure 1.3.