Instruction Manual
D200126X012
2502 Controllers
June 2017
17
W
d
= Weight of the displacer, in pounds (determine by weighing displacer).
0.0361 = Weight of one cubic inch of water (specific gravity = 1.0), in pounds.
V = Volume of the displacer in cubic inches, that would be submerged at the level required by the calibration
procedure. Or,
V =
π
/4 (displacer diameter)
2
x (length of displacer submerged)
SP GR = Specific gravity of the process liquid at operating temperature.
For interface level measurement, the equation becomes:
W
s
= W
d
‐ [(0.0361) (V
1
) (SP GR
1
) + (0.0361) (V
h
) (SP GR
h
)]
where:
V
1
= Volume of the displacer submerged by the lighter liquid, in cubic inches.
Or,
V =
π
/4 (displacer diameter)
2
x (length of the displacer submerged)
SP GR
1
= Specific gravity of the lighter liquid at operating temperature.
V
h
= Volume of the displacer submerged by the heavier liquid, in cubic inches.
Or,
V =
π
/4 (displacer diameter)
2
x (length of the displacer submerged)
SP GR
h
= Specific gravity of the heavier liquid at operating temperature.
Calibration Procedure
WARNING
The following calibration procedure requires taking the controller out of service. To avoid personal injury and property
damage caused by an uncontrolled process, provide some temporary means of control for the process before taking the
controller out of service.
Figure 9 shows adjustment locations for the following steps, except as otherwise indicated. When calibrating, open
loop conditions must exist. One way to obtain an open loop is to place the final control element into manual control or
bypass it. If there is no provision for manual control, shut down the process. It is recommended that a test pressure
gauge be installed in the controller output line for subsequent calibration steps.
Several steps in these calibration procedures require setting the process variable at its minimum and maximum limits
according to table 2. Reverse‐acting controllers produce the opposite response.
Table 2. Minimum and Maximum Limits for Setting Process Variables
Application
Minimum Limit
Maximum Limit
Liquid level
Displacer must be completely out of liquid
Displacer must be completely submerged in liquid
Interface
Displacer must be completely submerged in the upper of
two process liquids
Displacer must be completely submerged in the lower of
two process liquids
Density
Displacer must be completely submerged in liquid having
highest specific gravity expected
Displacer must be completely submerged in liquid
having the lowest specific gravity expected
