The specific gravity of fuel can be changed in the field by plant personnel. If the specific gravity of actual fuel in your tank is higher than 0.88 the transmitter will indicate a fuel level that is higher than it really is. But if the specific gravity of actual fuel in your tank is lower than 0.88 the transmitter will indicate a fuel level that is lower than it really is. Incorrect indications can either lead to overflowing the tank when it is being filled or unintentionally running out of fuel.
RESETTING THE SPECIFIC GRAVITY
If you have fuel with a specific gravity different from 0.880 you should change the specific gravity setting of the transmitter.
NOTE: you cannot directly enter the numerical value for fuel specific gravity when resetting the transmitter. The numbers you actually set on the transmitter are the numbers shown in Figure 3 for the Full scale blind setting.
If you need to change the transmitter setting, compare the specific gravity of your fuel with those shown in Figure 3. Choose the specific gravity with a value closest to that of your fuel. Use the Full Scale Blind Setting shown for that value as the new setting of your transmitter.
The transmitter has a display window (Figure 2) and a set of magnetic pushbuttons (Figure 4). Use the magnetic pushbuttons on the transmitter to reset the transmitter.
First use pushbutton M to cause Mode 6 to show in the display window. Then use the other two pushbuttons to set the appropriate number from Figure 3. Press pushbutton M again to save your settings.
Figure 4. Magnetic pushbuttons.
The only configuration parameter that you can use to reset fuel specific gravity is Full scale “blind setting” or Mode 6. Do not change any other parameter!
FUEL LEVELS vs GALLONS
As already noted the transmitter indicates fuel levels in inches. You may need to know how many gallons of fuel that various levels represent.
The pressure transmitter is set up to indicate the height of fuel from the bottom of the tank.
The transmitter is installed with its sensor 16 inches above the bottom of the tank. (This distance may vary plus or minus 1/4-inch.) Consequently, the transmitter indicates 16 inches when the fuel level is at the same height as the sensor. When the fuel level is 16 inches there are approximately 941 gallons of fuel in the tank.
But note that the transmitter does not actually indicate fuel levels lower than 16 inches, even though the display continues to show 16.00. So remember, any time the transmitter display shows 16.00, the amount of fuel in the tank is somewhere between 0 and 941 gallons.
Figure 7 shows gallons of fuel in the tank for various inch-levels that correspond to the transmitter display. This figure is applicable for Heatec single-wall fuel tanks with an inside diameter of 131.5 inches and heights up 600 inches. Volumes are approximately 4 percent less for tanks with double walls. The information shown in Figure 5 is based on fuel at a temperature of 60 degrees F.
You should make allowances for changes in volume due to temperature, especially when filling the tank. Accordingly, you should allow about 10 percent for expansion. Figure 5 shows the maximum fill levels for Heatec fuel tanks with an allowance of 10 percent for expansion.
