Electrical switches can adapt to misunderstandings in the application / application to ensure no leakage current and make them available in multiple circuits, actuators, and housing styles. Disadvantages include their number, limited communication life cycle, large size and slow response.

Solid Switch

Solid switches electric appliances that do not have aging moving parts. They are able to switch quickly without any spark between contacts or problems with communication rust. Their disadvantages include high construction costs at current very high rates.

When selecting a level switch, the user needs to determine if the power circuit needs a switch that is usually open or closed.

Normally Open (NO)

The switches do not currently allow for free access. They need to “create” a contact in order to activate it.

Normally Closed (NC)

The switches currently allow free access and require a “break” contact (open) to be activated.

Stick / Throw

Most switches have one or two poles and one or two throws, but some manufacturers will produce custom-level switches for specialized apps. The number of poles indicates the number of different circuits that can be switched on at the same time.

The cast number describes the number of circuits each pole can control. This is indicated by a circuit configuration (NO / NC). Pause is a circuit breaker caused by contacts that are separated by a switch that introduces each circuit that opens or interrupts the circuit.

Electrical Changing System and Types

Single Pole, One Throw (SPST)

Single pole, single throw switches (SPST) make or break a single conductor connection in a single branch circuit. They usually have two terminals and are called single-pole switches

Single pole, Double Throw (SPDT)

A single pole, dual switches (SPDT) makes or breaks a single conductor connection with one of two conductors. They usually have three terminals and are usually used in pairs. SPDT switches are sometimes called three-way switches.

Double Pole, Single Throw (DPST)

Double pole, single throw switches (DPST) make or break the connection of two circuit conductors in a single branch circuit. They usually have six terminals and are available in both temporary and maintenance communication versions.

Double Pole, Double Throw (DPDT)

Double pole switches, double throw (DPDT) make or break the connection of two conductors in two different circuits. They usually have six terminals and are available in both temporary and maintenance communication versions.

Electrical switch contacts are either normally-open or normally-closed, depending upon the open or closed status of the contacts under “normal” conditions.

But what exactly defines “normal” for a switch? The answer is not complicated, but it is often misunderstood because of the ambiguous nature of the common word.

The “normal” state of the switch is the state of electrical contacts in the state of non-physical regeneration. One way to think of a “normal” situation is to think of a change in relaxation.

With the change of the temporary contact button, this may be the status of the switch contact if it is not pressed. Electric switches are always designed with scheme drawings in their “normal” conditions, regardless of the type of operation.

The “normal” state of the switch (closed) is actually an abnormal state of the internal process (low flow), for the simple reason that the switch should be stimulated and not rested while the process is running. as it should.

Below listing of “normal” definitions for various process switch types:

• Limit switch: target not contacting the switch
• Proximity switch: target far away
• Pressure switch: low pressure (or even a vacuum)
• Level switch: low level (empty)
• Temperature switch: low temperature (cold)
• Flow switch: low flow rate (fluid stopped)

Symbols of electrical switches

A pressure sensor simply monitors this pressure and can display it in one of the several units known around the world. This is commonly the “Pascal”, “Bar”, and “PSI” or pounds per square inch in the United States. The pressure of the air in your tire is a great example of pressure and how it is measured. As we air the tire up, the force it exerts on the tire increases, causing the tire to inflate. This is monitored with a pressure sensor inside the tire on newer vehicles.

So how does a pressure sensor work? In a nutshell, it converts the pressure to a small electrical signal that is transmitted and displayed. These are also commonly called pressure transmitters because of this. Two common signals that are used is a 4 to 20 milliamps signal and a 0 to 5 Volts signal.

Most pressure sensors work off of the piezoelectric effect. This is when a material creates an electric charge in response to stress. This stress is usually pressure but can be twisting, bending, or vibrations. The pressure sensor detects the pressure and can determine the amount of pressure by measuring the electric charge. Pressure sensors need to be calibrated so it knows what voltage or milliamp signal corresponds to what pressure. This is a basic “Zero” and “Span” calibration or minimum and maximum which is a common job for maintenance personnel.

In the article “What is Sensor Calibration and Why is it Important?” we described the sensor calibration in detail. What are some of the common types of pressure that you can measure with a pressure sensor? There are three common types that we use in the industry. First being “Gauge Pressure”. This is measured in reference to atmospheric pressure which is typically 14.7 PSI. You will show a “positive” pressure when it is above atmospheric pressure and a “negative” when it is below atmospheric pressure. The next type is “Absolute Pressure”. Simply put, this is the pressure as measured against absolute vacuum. A full vacuum will have an absolute pressure of 0 PSIa and increase from there. If you need to read a pressure that is lower than atmospheric pressure, this is the type of sensor you would use.

The last type that is commonly monitored in the industry is “Differential pressure”. This is exactly what it sounds like, the difference between two pressures, a pressure being measured and a reference pressure. In industry, pressure sensors are used for a wide variety of processes. Some common uses are to measure the pressure of steam. Steam is commonly used to heat many processes in manufacturing facilities. This pressure sensor on the steam system can serve multiple purposes though. First and most obvious is to observe and monitor the pressure. Another purpose is to control when and where steam can flow and regulate its pressure. Steam can build up a pressure in a vessel and become dangerous. We can use the pressure sensor as an input device to open and close a control valve to keep the pressure and steam flow regulated. This only requires simple programming in the PLC to achieve this.

Pressure sensors are also installed next to filters in many industrial processes. If the filter begins to clog, the flow will decrease. As the flow of the liquid decreases, pressure can increase or decrease depending on which side of the filter is monitored. If you monitor the pressure, it will give you a simple indication that the filter is clogged and needs to be cleaned or replaced.

A common use that isn’t as obvious is the use of a pressure sensor as a level sensor. In an open tank, you can use the hydrostatic pressure that is measured at the sensor. With a little math, using the size of the tank and specific gravity of the liquid, we can determine how much of that liquid is in the tank. If the tank is closed, it isn’t as simple of an installation. It is still a viable option though. This will require at least two sensors to measure differential pressure. The high-pressure sensor would be located at the bottom of the tank measuring the liquid pressure and the low-pressure sensor near the top measuring the air pressure inside. A calculation can then be performed to figure out how much liquid is in the tank.

Let’s take a look back at what we have learned. Pressure is an expression of force exerted on a surface per unit area. The standard units are the Pascal, Bar, and PSI or pounds per square inch. Pressure sensors convert the pressure into an electrical signal that can be transmitted and displayed. This is why many sensors are referred to as transmitters. These sensors commonly measure Gauge Pressure, Absolute Pressure, and Differential Pressure. Gauge pressure is measured against the atmospheric pressure, absolute is measured against a vacuum, and the differential pressure is the difference between two pressures. Pressure sensors are commonly used to monitor pressures in different processes. A common thing to monitor is steam pressure. That pressure sensor can be used to control a valve to keep steam pressure at a constant level. Another common but lesser known use is to monitor the level of a liquid in a tank. Filter clogs are a common use of differential pressure monitoring. By knowing the pressure before and after the filter, you can determine if it is clogged.