CALIBRATION OF DP LEVEL TRANSMITTER :

To do the calibration of the level transmitter we have to calculate the value of the LRV (lower range value) and URV (upper range value).


There are threeway of installing the transmitter which is listed below,


1. Zero elevation

2. Suppression

3. Elevation


Here we will be discussing zero elevation, here we only will discuss equation for both open tank and closed tank.

To calculate differential pressure due to tank is open DP type transmitter's LP side is open to the atmosphere so, it will compensate pressure of the atmosphere.


DP = HP - LP

= (P(atm) + P(liquid)) - P(atm)


DP = P(liquid)


If the tank is closed then,


1. DRY LEG (Not anything is filled in it)


Differential pressure is given by,

DP = (P(liquid) + P(vapour)) - P(vapour)

Due to P(vapour) cancels out,


DP = P(liquid)


Here the tank is closed so on HP side pressure will be the sum of filled liquid and vapour pressure. On the LP side due to dry leg, there is nothing filled inside so, only pressure act is due to vapour.


2. WET LEG (FILLED LIQUID- MOSTLY GLYCOL)


Here we have filled liquid is there which is mostly glycol.

Now Differential Pressure is given by,


DP = HP - LP

= (P(liquid) + P(vapour)) - (P(vapour + P(SF))

where, SF(sealed fluid)- specific gravity of filled liquid in a wet leg.

Due to the cancellation of Pvapour,


DP = P(liquid) - P(SF)


Above all the calculation is required to calculate LRV for the transmitter. In the next article, I will be discussing calculation of LRV and URV with the help of an example.

CALIBRATION

CONTROL VALVE

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