single element drum level contrl

Hi there,

The answer is not so simple. You need to provide a few facts first.

1. Is the drum closed or open to atmosphere?

2. Is the liquid in the drum under pressure and/or temperature?

3. What is the liquid type you are measuring?

4. What accuracy to you need?

To answer your question very simply.

A DP cell consists of two cells - high pressure and low pressure.

You would connect the HP side to the bottom of the drum (lowest measuring point) and the LP side to the top of the drum (highest measuring point).

To get the level is simple from here: Pressure = Height x Density x Gravity (P=HDG)

we Know G = 9.98m/s

You will know the height as you will measure this between the two takeoff points. The density you will get from your chemical engineer.

You will then work out the pressure at MAX height i.e. full reading and calibrate your transmitter for that range. The transmitter should then give you a 4-20mA signal corresponding to the height or % level. Be carefull of the SI units you use here as we work to mmH2O or kPa and cm.

Please bear in mind that I have not taken into account the need for a wet leg installation (the DP decreases as the level increases - opposite of above) nor have I taken into account pressure, pressure or density fluctuations or compensated for them.

Regards,

Craig

If G is the earth acceleration or gravity there are 2 errors :

- units m/s²

- value roughly 9.81 depends on position

LOL yes - but i couldb't find the power sign and was too lazy to look. I am in the Southern hemisphere (South Africa) and we use 9.98. You are correct that is why I provided the descriptors of the formula so that they may apply it to their location

Regards,

Craig