DP Level Transmitter Elevation and Suppression Corrections

DP Transmitter Elevation and Suppression Corrections for Level Measurement

When installing a DP transmitter to measure liquid level, configuration of the transmitter often must include an adjustment for one of two conditions introduced by the mounting arrangement.

Elevated Span

The Lower Range Value (LRV) of the transmitter needs to be configured above “0.”

 Suppressed Span

The LRV of the transmitter needs to be configured below “0.”

A brief discussion of how to make adjustments for elevation and suppression follows. Then two examples of the calculations needed to determine configuration parameters are given. Finally, a brief procedure that does not involve calculations is provided.

The range of the transmitter can be set anywhere, forward or reverse acting, as long as the following criteria are met:

LRL ≤ LRV ≤ URL
LRL ≤ URV ≤ URL

Span = [URV – LRV] ≥ Min Span

Note that the URL (Upper Range Limit), LRL (Lower Range Limit), and Min Span are transmitter dependent.

 Transmitter Elevation Calculation Example 

The below figure shows a sample transmitter installation.

1. Calculate the differential pressure as follows.

Pressure_@DP = (H × SpG)_{High Side} – (H × SpG)_{Low Side}

where H = Height

2. Calculate the LRV when the tank is empty.

LRV = (120 x 1.0)_{High Side} – (0 x 1.0)_{Low Side}

LRV = +120 inH2O

3. Calculate the URV.

URV = LRV + Span
URV = +120 + 100
URV = 220 inH2O

Therefore, transmitter range should be 120 to 220 inH2O

 Transmitter Suppression Calculation Example

The below figure shows a sample transmitter installation.

1. Calculate the differential pressure as follows.

Pressure_@DP = (H × SpG)_{High Side} – (H × SpG)_{Low Side}

where H = Height

2. Calculate the LRV when the tank is empty.

LRV = (0 x 1.0)_{High Side} – (100 x 1.0)_{Low Side}

LRV = -100 inH2O

3. Calculate the URV.

URV = LRV + Span
URV = -100 + 100
URV = 0 inH2O

Therefore, transmitter range should be -100 to 0 inH2O

Source : Siemens Pressure Transmitter

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