# Autolevel

### Introduction

Level transmitter configuration can be very time consuming. Calculations required to determine proper range values for traditional transmitters can become complex due to the physical layout of an application.

With maintenance shops getting smaller, finding equipment that allows us to do more with fens becomes a priority. DPharp transmitters with advanced software functionality can eliminate these complex calculations.

### Application

Using typical smart or conventional products, all the following must be considered:

 The specific gravity of the process SGP Precise location of 0% and 100% Specific Gravity of the capillary fill fluid    (or sealing fluid used in impulse piping) SGFF Exact orientation oi the transmitter to the vessel H2 Vertical distance between the process conn. H1

Depending on the application, the vessel may be open (referencing atmosphere) or closed (under a blanket pressure).

Elevation is typically used when the vessel is closed. To reference the blanket pressure, a low side remote seal may be used (or a wet leg). The capillary on remote seal creates a negative force on the transmitter equal to the vertical height times the specific gravity of the fill fluid.

Elevation = (H1 + H2) x SGFF

Suppression is a positive pressure created on the high-pressure side of the transmitter typically due to the transmitter being positioned below the 0% process connection. Suppression is present in both open arid closed vessels. Suppression is equal to the vertical distance between the 0% process connection and the transmitter times the Specific Gravity of the fill livid.

Suppression = H2 x SGFF

Span is the vertical distance between the process connections times the process medium's Specific Gravity.

Span = H1 x SGP

Figure 1: Closed Tank

Now that you have the Elevation, Suppression, and Span, the calibration values can be calculated for the 0% (Empty) arid the 100% (Full).

Cal Value (0%) = Suppression - Elevation

Cal Value (100%) = (Suppression + Span) - Elevation

Example: (using figure 1)

 SGP 0.9 H2 10 inches SGFF 0.8 H1 20 inches

Cal Value 0%) = Suppression - Elevation
Cal Value (0%) = (H2 x SGFF) - (H1 + H2 x SGFF)
Cal Value (0%) = (10 x 0.8) - (20 + 10) x 0.8
Cal Value (0%) = 8 - 24
Cal Value 0%) = -16 inH2O

Cal Value (100%) = (Suppression + Span) - Elevation
Cal Value (100%) = ((H2 x SGFF) + (H1 x SGP)) - (H1 + H2) x SGFF
Cal Value (100%) = ((10 x 0.8) + (20 x 0.9)) - (20 + 10) x 0.8
Cal Value (100%) = (8 + 18) - 24
Cal Value (100%) = +2 inH2O

Therefore, Calibrated Range would be:

 -16 inH2O +2 inH2O 0% 100% Empty Full

### Related Products & Solutions

#### Absolute Pressure

Absolute Pressure transmitters compare a pressure relative to Absolute pressure. Absolute pressure is always a positive value.

#### Differential Pressure

Differential Pressure (DP) is defined as the difference between two pressures. Differential Pressure Transmitters use a reference point called the low-side pressure and compare it to the high-side pressure. Ports in the instrument are marked high-side and low-side.

#### Draft Pressure

Draft Pressure transmitters are a unique type of differential transmitter that is designed to measure small differences in very low static pressure environments.

#### Gauge Pressure

Gauge Pressure transmitters compare a pressure relative to atmospheric measure.

#### Liquid Level

Accurate level readings are essential to the safe, reliable, profitable operation of your plant. Liquid Level transmitters measure differential pressure to infer the level in a vessel.

#### Low Flow

Using Bernoulli's equation, Differential Pressure transmitters can be used to infer the flow of fluid through a pipe.

#### Mass Flow (Multivariable)

There are several technologies on the market to measure mass flow. One is the Multi-variable Pressure Transmitter.

#### Pressure Transmitters

The accurate and stable measurement of process pressure with Yokogawa Pressure Transmitters supports the safe, reliable, and profitable operation of your plant.

×