Flowline LD35 DeltaSpan - Manual (Page 9)

Rev B MN301035 9 of 16
GETTING STARTED (continued) Step Six
How to select the correct pressure transmitter?
The objective is to select a sensor with an operational range that will cover the entire application span. If the
liquid height of the tank is above the sensor’s Maximum Liquid Height, then the sensor will not be able to
read a full tank level. Compare the tank’s Pressure @ Full against the sensor’s pressure range to select a
sensor.
To calculate the tank’s Pressure @ Full, use the following formula:
Pressure @ Full = [Height @ Full Tank (feet) x SG] / 2.31 (feet/psi)
Pressure @ Full = [Height @ Full Tank (meters) x SG] / 0.704 (m/psi)
To select the correct pressure transmitter, follow the steps below:
 Measure the Height @ Full Tank (in feet or meters).
 Determine the SG for the liquid (if the customer does not know, check the MSDS sheet).
 Use the formula above to calculate the Pressure @ Full.
a. Example: A 40’ tank with a liquid media SG of 0.9 has a Pressure @ Full of 15.58 psi.
b. [(40’ x 0.9) / 2.31’/psi] = 15.58 psi
 Select a pressure transmitter with a pressure greater than or equal to the Pressure @ Full.
a. In the example above for a 40’ tall tank with a SG=0.9, you need a pressure range greater than
or equal to 15.58 psi.
b. Using a sensor with a pressure range of 20 psi provides a Maximum Liquid Height of 51.33’,
which will read the entire range of the 40’ tall tank.
c. Using a sensor with a pressure range of 15 psi provides a Maximum Liquid Height of 38.50’,
which is short by 1.5’.
i. This means that the sensor will output 20 mA at 38.5’ of liquid and the top 1.5’ of liquid
will not be measured.