1. Ionization sensors (detectors) In an ionization sensor, the radiation passing through a medium (gas or solid) creates electron-proton pairs Their density and energy depends on the energy of the ionizing radiation. These charges can then be attracted to electrodes and measured or they may be accelerated through the use of magnetic fields for further use. The simplest and oldest type of sensor is the ionization chamber.

2. Ultrasonic transmitters Guided-wave radar transmitters Measurement Principle Sound wavesHigh-frequency radar impulses Contact Type Noncontact measurementContact measurement Operating Limits Limited operating pressures and temperatures High temperatures and pressures do not affect device performance Mounting Top-mounted Environmental and Application Conditions Conditions affect measurement performance Not affected by environmental and application conditions Overall Performance Acceptable Performance is based on strength of the reflected sound wave or echo Exceptional Performs well independent of process conditions

3. Radiation sensors Will start the discussion with ionization sensors Then will discuss the much lower frequency methods based on electromagnetic radiation Three basic types of radiation sensors: – Ionization sensors – Scintillation sensors – Semiconductor radiation sensors These sensors are either: – Detectors – detection without quantification or: – Sensor - both detection and quantification