# CALIBRATION OF DP (Differential Pressure) LEVEL TRANSMITTER(ZERO ELEVATION) :

Updated: Jan 26

In the last article, we discussed the basic equation for the calibration of Differential Pressure or DP level transmitter which we will use in this article.

In this article, we will calculate the level for the closed tank when the transmitter is at zero elevation for the calibration.

Zero elevation means the transmitter is installed at zero percentage level (0% - 4mA)

We then use calculated value to enter in the transmitter.

1. DRY LEG CALIBRATION :

In order to calculate URV and LRV let's consider an example shown in the above figure. let consider tank has a height of 8200 mm and the specific gravity of a liquid is 1.14.

1) First, we have to calculate Range,

Range = height of the tank (0% to 100%) * S.G. of liquid

= 8200 * 1.14

Range = 9348 mmH20

2) Now let's calculate LRV (Lower range value - 0%)

Here Due to the transmitter is at zero elevation we only left with the pressure of a liquid and we are at LRV answer will be zero.

LRV = HP - LP

= (Pliquid + Pvapour) - Pvapour

Pvapour cancels out,

= Pliqhid

LRV = 0 mmH20

3) Now calculate URV (Upper range value)

URV = LRV + Range

= 0 + 9348

URV = 9348 mmH20

After getting a value of LRV and URV we just have to put that value in our transmitter.

2. WET CALIBRATION :

Let calculate LRV and URV for the above-shown fig. Consider height between LRV and URV is 7270 mm and height of the sealed liquid column is 8210 mm. S.G. of filled liquid is 0.92 and for sealed liquid is 0.94.

1) Calculate Range

Range = S.G. of liquid * Height (0% to 100%)

= 0.92 * 7270

Range = 6688.4 mmH2o

2) Calculate LRV

LRV = HP - LP

= (Pliquid + Pvapour) - (Pvapour + Psf)

Pvapour cancels out,

= Pliquid - Psf

= 0 - (8210 * 0.94)

LRV = -7717.4 mmH2o

3) Calculate URV

URV = LRV + Range

= -7717.4 + 6688.4

URV = -1029 mmH20

Simply put a calculated value of LRV and URV in the transmitter.

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