1. Level Measurement Muhajir Ab. Rahim School of Mechatronic Engineering Universiti Malaysia Perlis

2. Introduction Most industrial process use liquids such as water, chemical and fuels. These materials are stored in container ready for on-demand use. It is very important to know the level and remaining volumes of these materials.

3. Level Formulas We can correlate the value of displacement or height of liquid based on the following formulas. ∆P = ρg∆h So, ∆h = ∆P/ρg Cd = Caμd + Ca So, d = (Cd-Ca)r r μdμd ∆h d r Ca = capacitance with no liquid μ = dielectric constant of the liquid between the plate r = height of the plates d = depth or level of the liquid between the plates

4. Level Sensing Devices There are two categories of level sensing devices. 1) Direct sensing 2) Indirect sensing

5. Direct Level Sensing Examples of direct level sensing are; 1)Sight glass 2)Float 3)Probes – conductive, capacitive, ultrasound

6. Conductive probe Capacitive probeUltrasound transmitterreceiver

7. Indirect Level Sensing In this method, the property of the liquid such as pressure is sensed to determine the liquid level. Example of indirect level sensing techniques are; 1) Bubbler technique- measuring pressure 2) Radiation technique- measuring radiation 3) Resistive tapes- measuring resistance 4) Load cells – measuring weight 5) Paddle wheel- measuring torque

8. Bubbler technique Radiation technique Resistive tape techniquePaddle wheel technique transmitter receiver

9. How to Select? You need to understand the characteristic of your system. For examples, the pressure, liquid temperature, turbulence, corrosiveness, accuracy.. You also need to consider the limitation of your instrumentation.

10. Quiz What is the depth of a liquid in a container, if the specific weight of the liquid is 82 lb/ft 3, the container weight is 45 lb, with 21 inch in diameter? Assume a load cell measures a total weight of 385 lb.