TILI Automation

 In this article, you will learn the basics of the managed switch and unmanaged switch in networking. The network Switch is one of the most important parts of any network. All the communications going on a network are only possible because of a network switch. The network switch receives data from one port and sends the data to the other port or the correct location. Because of this functionality, the network switch is also called the brain of any network. Because the network switch manages the data communication between all the devices on the network. Any Network Switch can be classified on the basis of the number of ports. The most common type of network switch is 24-port and 48-port network switches in industrial applications. But one of the main parameters which differentiate network switches is whether the switch is managed network switch or an unmanaged network switch. What is the difference between a managed network switch and an unmanaged network switch? One of the most bas...

 A limit switch is an electromechanical unit that consists of an actuator that is connected mechanically to the set of contacts. When the object travels towards and comes in touch with the actuator, the limit switch performs the contacts to make or break an electrical connection. Limit Switch Mechanical limit switches consist of a mounted actuator arm that operates a set of electrical contacts when the arm is dislocated. Limit switch failures are generally mechanical in nature. Principle: Automatic operation of a machine requires the use of limit switches that can be activated by the motion of the machine. A limit switch is used to convert this mechanical motion of the machine to an electrical signal to switch circuits. The operating position of the limit switch is where the limit switch changes from its normal (NO or NC) to its operating state. The release position is where the contact change from their operating state to their normal state. Types of Mechanical limit switches Leve...

 Perhaps the simplest (and oldest) form of electrical level detection is where a pair of metal electrodes contacts the process material to form a complete electrical circuit, actuating a relay. This type of switch, of course, only works with granular solids and liquids that are electrically conductive (e.g. potable or dirty water, acids, caustics, food liquids, coal, metal powders) and not with nonconducting materials (e.g. ultra-pure water, oils, ceramic powders). A legacy design for conductive level switches is the model 1500 “induction relay” originally manufactured by B/W Controls, using a special transformer/relay to generate an isolated AC probe voltage and sense the presence of liquid: Conductive Level Switch Line voltage (120 VAC) energizes the primary coil, sending a magnetic field through the laminated ferrous core of the relay. This magnetic field easily passes through the center of the secondary coil when the secondary circuit is open (no liquid closing the probe circui...

 A pressure switch is one detecting the presence of fluid pressure. Pressure switches often use diaphragms or bellows as the pressure-sensing element, the motion of which actuates one or more switch contacts. Recall from Basics of Switches article, that the “normal” status of a switch is the resting condition of no stimulation. A pressure switch will be in its “normal” status when it senses minimum pressure (e.g. an applied pressure, or in some cases a vacuum condition). For a pressure switch, “normal” status is any fluid pressure below the trip threshold of the switch. The following photograph shows two pressure switches sensing the same fluid pressure as an electronic pressure transmitter (the device on the far left) because they are all plumbed to a common tube: A legacy design of pressure switch uses a bourdon tube as the pressure-sensing element, and a glass bulb partially filled with mercury as the electrical switching element. When applied pressure causes the bourdon tube to...

 Another electronic liquid level switch technology is capacitive: Sensing level by changes in electrical capacitance between the switch and the liquid. The following photograph shows a couple of capacitive switches sensing the presence of water in a plastic storage vessel: Capacitive Level Switch Advantages Capacitance techniques are capable of operation at extremes of temperature and pressure. They work well for materials that won’t leave a coating. Usually only a single tank penetration is required. Disadvantages Capacitance systems are intrusive. Have problems with varying dielectric materials and those media’s, that coat the sensing element. Thus users are normally limited to water-like media. Even acids and caustics that don’t appear to coat the sensing element are so conductive that the thin film they leave can cause serious errors in measurement. Practical Notes Most users’ realise the limitations of Capacitance level measurement, such as the large errors caused by coatings....

 Some level switches use a float to sense the level of a liquid surface, actuating an electrical switch by the motion of the float. The electrical schematic symbol for a level switch is actually based on this type of mechanism, with a round “ball” float drawn as the actuating element: An example of this technology is a level switch manufactured by Magnetrol, with two such switches shown in the following photograph of a steam boiler. These switches sense water level in the steam drum of the boiler: Float level switch The Magnetrol float switch mechanism uses a mercury tilt bulb, tilted by a magnet’s attraction to a steel rod lifted into position by a float. The float directly senses liquid level, positioning the steel rod either closer to or farther away from the magnet. If the rod comes close enough to the magnet, the mercury bottle tilts to change the switch’s electrical status: A feature of this design is complete isolation between the electrical components and the “wet” componen...

 Tuning Fork Level Switch uses a metal tuning fork structure to detect the presence of a liquid or solid (powder or granules) in a vessel: Tuning Fork Level Switch An electronic circuit continuously excites the tuning fork, causing it to mechanically vibrate. When the prongs of the fork contact anything with substantial mass, the resonant frequency of the fork decreases. The circuit detects this frequency change and indicates the presence of mass contacting the fork. The forks’ vibrating motion tends to shake off any accumulated material, such that this style of level switch tends to be resistant to fouling. It should be noted that the previous photograph of the tuning-fork style level switch is complete: the fork “paddles” are only a couple of inches long and require no physical extensions in order to properly detect liquid or solid material at that point.

 A more primitive variation on the theme of a “tuning fork” level switch is the rotating paddle switch, used to detect the level of powder or granular solid material. This level switch uses an electric motor to slowly rotate a metal paddle inside the process vessel. If solid material rises to the level of the paddle, the material’s bulk will place a mechanical load on the paddle. A torque-sensitive switch mechanically linked to the motor actuates when enough torsional effort is detected on the part of the motor. A great many level switches of this design sold in the United States under the trade-name Bindicator (so-called because they detected the level of solid material in storage bins). Paddle Wheel Level Switch A “Bindicator” style of level switch appears in this photograph (painted black, against a white painted hopper), used to detect the presence of soda ash powder in a hopper at a water treatment plant.

 Yet another style of electronic level switch uses ultrasonic sound waves to detect the presence of process material (either solid or liquid) at one point: Sound. Sound waves pass back and forth within the gap of the probe, sent and received by piezoelectric transducers. The presence of any substance other than gas within that gap affects the received audio power, thus signaling to the electronic circuit within the bulkier portion of the device that process level has reached the detection point. The lack of moving parts makes this probe quite reliable, although it may become “fooled” by heavy fouling.

 A temperature switch is one detecting the temperature of some substance. Temperature switches often use bimetallic strips as the temperature-sensing element, the motion of which actuates one or more switch contacts. Temperature Switch Principle An alternative design uses a metal bulb filled with a fluid that expands with temperature, causing the switch mechanism to actuate based on the pressure this fluid exerts against a diaphragm or bellows. This latter temperature switch design is really a pressure switch, whose pressure is a direct function of process temperature by virtue of the physics of the entrapped fluid inside the sensing bulb. The “normal” status of a switch is the resting condition of no stimulation. A temperature switch will be in its “normal” status when it senses minimum temperature (i.e. cold, in some cases a condition colder than ambient – check below note). For a temperature switch, “normal” status is any sensed temperature below the trip threshold of the switch...

 A flow switch is one detecting the flow of some fluid through a pipe. Flow switches often use “paddles” as the flow-sensing element, the motion of which actuates one or more switch contacts. Principle of Flow Switch The “normal” status of a switch is the resting condition of no stimulation. A flow switch will be in its “normal” status when it senses minimum flow (i.e. no fluid moving through the pipe). For a flow switch, “normal” status is any fluid flow rate below the trip threshold of the switch. A simple paddle placed in the midst of a fluid stream generates a mechanical force which may be used to actuate a switch mechanism, as shown in the following photograph: Like all other process switches, flow switches exhibit deadband (also called differential ) in their switching action. A flow switch that trips at 15 GPM rising, for example, will not re-set at 15 GPM falling. That switch would more likely reset at some lower flow rate such as 14 GPM. With the “trip” and “reset” points ...

 Relay Working Animation shows the operation of relay visually. The NO & NC contacts of relay will change on giving control signal. When control signal is given to the coil of relay and the coil is magnetized. After relay magnetization, the contact of relay changes from N.O to N.C. or Vice versa. When the coil is De-magnetized then the relay contacts again change to its initial state. Relay Working Animation Relay Principle Animation Relay Working Animation

  Here in our Animation, The raise in liquid level lifts the float and this in turn moves the magnet closer to the reed switch. when magnet comes near to reed switch, the output contact changes. The change in contact is a signal of liquid level raise or vice versa. The purpose of a float level switch is to open or close a circuit as the level of a liquid rises or falls.  All float operated liquid level controls operate on the basic buoyancy principle which states “the buoyancy force action on an object is equal to the mass of liquid displaced by the object.” As a result, floats ride on the liquid surface partially submerged and move the same distance the liquid level moves. Because of this, they are normally used for narrow level differential applications such as high level alarm or low level alarm. To complete a circuit, float switches utilize a magnetic reed switch, which consists of two contacts sealed in a glass tube.  When a magnet comes close to the two contacts, th...

 The purpose of a float level switch is to open or close a circuit as the level of a liquid rises or falls.  All float operated liquid level controls operate on the basic buoyancy principle which states “the buoyancy force action on an object is equal to the mass of liquid displaced by the object.” As a result, floats ride on the liquid surface partially submerged and move the same distance the liquid level moves. Because of this, they are normally used for narrow level differential applications such as high level alarm or low level alarm. To complete a circuit, float switches utilize a magnetic reed switch, which consists of two contacts sealed in a glass tube.  When a magnet comes close to the two contacts, they become attracted to each other and touch, allowing current to pass through.  When the magnet moves away, the contacts demagnetize and separate (breaking the circuit), as shown below figure. In a float switch, the magnetic reed switch is hermetically sealed ...

 A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications. Fig : A wheel containing two magnets passing by a Hall effect sensor In its simplest form, the sensor operates as an analog transducer, directly returning a voltage. With a known magnetic field, its distance from the Hall plate can be determined. Using groups of sensors, the relative position of the magnet can be deduced. Frequently, a Hall sensor is combined with circuitry that allows the device to act in a digital (on/off) mode, and may be called a switch in this configuration. WORKING PRINCIPLE A Hall probe contains an indium compound semiconductor crystal such as indium antimonide, mounted on an aluminum backing plate, and encapsulated in the probe head. When the Hall probe is held so that the magnetic field lines are passing at right angles through the sensor o...

 Flow Switch operating principle is based on a free floating magnetic piston which responds only to the motion of fluids within the line, not to static or system pressures. In the presence of fluid flow, controlled movement of the piston actuates an external hermetically sealed reed switch. This switch can be used to actuate audible or visual alarms, as well as relays, or other controls. The piston’s movement by the fluid flow can be seen in the animation flow switches are used to determine if the flow rate is above or below a certain flow rate. This value (the set point) can be fixed or adjustable. When the set point is reached, the response can be the actuation of an electric circuit. When the flow switch is actuated, it will stay in that condition until the flow rate moves back from the set point by some amount.

 For decades, process instrumentation specifiers have faced the decision whether to use a switch or a transmitter for a given application. Either type of instrument can be used to effectively control industrial processes and protect equipment and personnel – and each has associated pros and cons. Application specifics typically drive decision-making, dictating which approach is most effective from performance, cost and life-cycle support perspectives. At its most basic, a switch acts in a binary fashion, changing state when a pressure, temperature, level or other process variable crosses over some predefined threshold. If the process variable in question can be allowed to vary in the course of normal operation, a simple switch linked to an on/off valve or pump can effectively and reliably control the process at hand, keeping a tank from running dry or a temperature from climbing too high. Even now, in order to control a relatively simple process, to reduce the cost of construction,...

 An ultrasonic switch is a device that uses inaudible high-frequency sound (ultrasound) to detect the presence or absence of a liquid at a designated point. The device consists of an electronic control unit and a sensor. Ultrasonic level switches use the properties of sound transmission in vapor and liquids to detect liquid level. When sound travels in air, it loses a great deal of signal strength. When traveling in liquid, sound retains almost all of its signal strength. To detect liquid level, we must determine if there is a liquid or gas (air) in the gap. Since liquids have a higher density than gasses, it is easier to transmit sound through them. One side of the sensor gap transmits sound, the other side detects it. When liquid is present, a high amount of sound is received at the detection side. When gas (air) is present, a small amount of sound is received. The electronics detect this difference and switch a relay accordingly. Ultrasonic switch sensors contain two piezoelectr...

 All float-operated liquid level switches operate on the buoyancy principle: “the buoyant force acting on an object is equal to the mass of liquid displaced by the object”. As a result, the partially submerged float moves with the level of the liquid in the vessel. Floats are most-commonly used for narrow level differential applications such as high level and low level alarms. The Float level switches use a float containing an internal magnet and a stem with an encapsulated, hermetically-sealed reed switch. As the float rises and falls with the liquid level, its internal magnet causes the switch circuit to open and close. The non-magnetic stem isolates it from the process. Float-type level controls are available for top mounting, side mounting and external chamber applications. Single and multi-level models are used to monitor preset liquid or liquid interface levels. Optional internal thermostats and RTD’s also monitor process temperature within the same sensor.

 In Line Flow Switch are comprised of two main assemblies: the housing and the shuttle assembly. As liquid flow enters the flow switch, it passes through an orifice between the inlet and outlet ports. When the flow reaches the switch’s setpoint, a magnet shuttle overcomes the downward force of a return spring and actuates a hermetically sealed SPDT reed switch element inside the bonnet stem. As the flow decreases, the spring overcomes the lifting forced created by the liquid and deactivates the switch. In Line Flow Switch Liquid Flow Monitoring: Flow switches are commonly used at multiple points in these types of water applications. The flow switch provides pump protection by detecting a no flow condition of the water in the process which prevents damage to the pump, before the line is pumped dry.