What exactly is a pressure switch?
This is a device with the ability to detect any changes in pressure and uses the change to either open or close an electrical contact.
It can either be when pressure falls or rises. It will only act when a given magnitude of pressure has been attained at its input.
It’s configured to respond in a certain manner depending on the pressure level. It’s mostly used to monitor various industrial processes. These switches are represented in a circuit diagram as shown below:
Broadly, these types of switches can be classified as either solid state or electromechanical switches.
The diagram shows the internal structure of a pressure switch.
The electromechanical types
These types of switches have two major components; the sensing element and the electrical snap-action switch.
They’re very many types of electromechanical pressure switches which can be classified depending on the type of sensing technology used. Some of the most common types include:
The diaphragm switches; the weld-sealed diaphragm acts as the switch and they can withstand a pressure of up to 150 psi. They have an accuracy of ±0.5% and are also characterized with low cycle rates.
The bourdon tube switches; they can operate in pressures between 50 psi to 18,000 psi. Like the diaphragm types, they have an accuracy of ±0.5% and are also characterized with low cycle rates.
The Dia-seal piston switches; they can operate in pressures which range from vacuum to about 1,600 psi. Their accuracy is ±2% and can go up to 2.6 million cycles.
Piston switches; they have an accuracy of ±2% and they can also operate at pressures of about 12,000 psi.
The solid-state switches
Most electromechanical switches had a lot of setbacks and hence, there was need to get more efficacious pressure switches. The first solid-state switch was introduced by 1980.
They have better accuracy (±0.25%); resistant to vibrations and shock; can handle very many pressure systems; durable; stable and have a broad frequency response.
Despite all these advantages, in an electromagnetic setup, most signals transmitted by these sensors can be corrupted. Furthermore, their initial cost is also higher.
Characteristics of pressure switches
While choosing switches, there are a number of factors one must have in mind. These include ease to use, reliability, accuracy and ability to fulfill the required objectives. Some of the most basic characteristics of these switches include:
The switching frequency; this directly affects the lifespan of the switch. For cases where the switch is turned ON and OFF more frequently, going for solid-state switches with about 100 million cycle life is desirable than the electromechanical switches such as bourdon tube which have about 1 million cycle life.
Cycle speed; go for a solid-state switch if the cycle rate is above 50 cycles/minute and a bourdon tube if the cycle rate is less than 25 cycles/minute. It will also determine the life span of the switch.
Operating pressure range; it will determine the accuracy of the switch. For instance, in a system where the switch should be active at 140 psi, it will require a switch whose operating range is 150 psi.
Proof pressure; while determining this pressure, all surges and spikes must be included. This is the maximum pressure the switch can be exposed to. They must not exceed the normal operational pressure. Other characteristics include the accuracy and the switching points.
These switches are very vital in an industrial setup since they can be used to stop various operations which tend to exceed the recommended limits. They make the automation process easier.