A proximity switch is the common name for a range of detectors that generate an electrical signal when a physical mass cuts through their sensor field. Upon detection of an object, the electrical signal is sent to a controlling device and is used to monitor and control the operation of the equipment.
Temperature Sensing Elements
A Brief Introduction to Temperature Sensing Elements
The temperature of a process is an important measure to know as it indicates whether or not the process is in control.
The selection of the temperature sensing method depends on
- the required temperature range
- the measuring accuracy required
- the speed of response needed from the control system
- the process chemicals and conditions
Capacitance Levels Probes
Capacitance level probes consist of a long rod or cable that protrude into a vessel and its contents. The instrument sets up an electric field between the probe and the tank wall using the contents of the tank as a dielectric (a nonconductor that allows an electric field to exist within itself). If the tank is non-metal, such as plastic or brick lined, two parallel rods are mounted in the level probe or a metal strip can be run on the outside of the tank. The electric field is set-up between the two probes or the probe and the metal strip. Figure 1 shows a simplified layout for a capacitance level probe. [Read more…]
Magnetic Flow Meters
Mag-flow meters are used to measure the flow velocity of conductive liquids. In a magnetic flow meter an electromagnet placed either side of the bore creates a magnetic field when the power is turned on. As the conducting liquid flows through the magnetic field a voltage is developed across the liquid. Insulated electrodes flush mounted in the wall of the meter detect the voltage. The magnitude of the induced voltage is proportional to the liquid velocity, the length of the meter and the strength of the magnetic field.
Keywords: electric current, isolation flanges, calibration. [Read more…]
Differential Pressure Transmitters
The differential pressure transmitter (PT) is used to detect a head of pressure.
The sensing element is connected to the process by pipework and flexes in proportion to the pressure. The resulting distortion produces an electric signal that is amplified and converted to a value on a read-out.
Keywords: pressure sensor, strain gauge, tank level, process pressure, pressure difference. [Read more…]