Introduction to Hydrostatic Level Part 2: Tank Control Using Relays
A tank's fluid level can be managed by using the 2450 Pressure/Hydrostatic Level Sensor and either the 8900 Multi-Parameter Controller or the 8250 Level Transmitter. With only two relays an operator can maintain a tank's fluid level and also send an alarm when the fluid level gets critically high or low. Use the setup information below for the following example.
8900 Relay Setup: Level units set to feet
Relay 1 Source: = Level L1
Relay 1 Mode: = Low
Relay 1 Setpnt: = 3.0000 ft
Relay 1 Hys: = 13.000 ft (Hysteresis)
Relay 2 Source = Level L1 (Level)
Relay 2 Mode: = Window
Relay 2 Rng: (range) min = 1.0000 ft
Relay 2 Rng: (range) max = 18.000 ft
Relay 2 Hys: (Hysteresis) = 0.5000 ft
8250-2 Relay Setup: Level units set to feet
Relay 1 Mode: = Low
Relay 1 Source: = LVL (Level)
Relay 1 Setpnt: = 3.0000 ft
Relay 1 Hys: = 13.000 ft (Hysteresis)
Relay 2 Mode: = Window
Relay 2 Source = LVL (Level)
Relay 2 Rng: (range) ft = 1.0000 to 18.000
Relay 2 Hys: (Hysteresis) = 0.5000 ft
Relay 1 Operation: When the fluid level drops below 3.0000 feet, Relay 1 will activate a valve/pump to start filling the tank. Because a hysteresis of 13.000 feet was programmed into the controller/transmitter, Relay 1 would deactivate the valve/pump once the tank's level reaches 16.000 feet (3.0000 feet plus the 13.000 feet Hysteresis).
Relay 2 Operations: The Window alarm mode of the controller/transmitter allows two separate set points to be entered. As long as the tank's fluids level is between the “Window” , or range, of 1.0000 to 18.000 feet, there is no alarm condition.
When the tank's level falls below 1.000 foot or exceeds 18.000 feet, Relay 2 would activate and could possibly send an audio/visual alarm, or shut down a process. The Hysteresis of 0.5000 feet would ensure that the Window alarm would activate until the minimum tank level is 1.5000 feet or the maximum tank level drops below 17.500 feet. The Window alarm could be an indicator of a faulty valve that does not shut off when the level reaches 16.000 feet, or a pump/valve failure if the fluid level never exceeds 1.5000 feet.
