The function of a pressure switch is to detect, display, alarm, and control signal outputs to ensure the normal operation of the system. It acquires and processes data through a high-speed MCU and uses a built-in precision sensor for compensation. It is a high-precision device for detecting pressure and liquid level signals, enabling pressure and liquid level monitoring and control. It is widely used in automated systems for measuring gas and liquid pressure in chemical, mechanical, hydrological, power, and environmental protection industries. Because of its convenient and flexible adjustment and simple installation, it can replace most applications where liquid level switches are used.

The principle of a pressure switch:

What is a pressure switch?

A pressure switch is a product used to detect pressure and output a switching signal when the pressure is higher or lower than a set point.

What is its function?

Used for protection, alarm, or control, for example:

Protection Function – Pressure vessels or pipelines have an upper pressure limit. As we all know, when the pressure is too high, exceeding the pressure limit, there is a risk of explosion. A pressure switch can be used as a pressure limiting sensor. By setting the set point of the pressure switch below the pressure limit of the vessel, when the pressure is too high, the switch will activate, opening valves or other pressure relief devices to achieve the protection purpose.

Alarm function – The pressure switch can be used in conjunction with a field flashing alarm. When the pressure is too high or too low, the switch will activate and the alarm will alert the field operator.

Control functions – Pressure vessels need to maintain stable pressure within a certain range. This can be achieved by setting upper and lower limits using a pressure switch. Furthermore, protection functions are also a type of control function.

According to principles:

Pressure switches can be divided into electronic pressure switches and mechanical pressure switches. Both of these categories include differential pressure switches, diaphragm pressure switches, etc.

Mechanical pressure switches rely on the elastic deformation and stroke of a pressure-sensing element to convert pressure into a switching signal, completing the switching action without the need for power supply.

Electronic pressure switches require power and obtain the corresponding mV signal from a pressure sensor. This signal is then converted by a circuit to produce a switching signal. Because the control circuit receives continuous mV values from the sensor, we can display the pressure inside the container in real time, compare it with the set value, and output a switching signal. The output includes a continuous 4-20mA analog signal and an RS485 signal. Its functionality is significantly more powerful than that of mechanical pressure switches.

As mentioned earlier, both of these categories include differential pressure switches and diaphragm pressure switches. What are they?

Differential pressure switch – measures the difference between two pressures and compares it with a set point. If the pressure is higher or lower than the set point, the switch will activate.

Diaphragm pressure switches – the pressure-sensing part is a flat diaphragm. This diaphragm collects the pressure inside the pipeline and transmits the pressure to the pressure diaphragm via internal silicone oil. The outer protective diaphragm is corrosion-resistant and scratch-resistant, making it widely used in applications with viscous media and high hygiene requirements. Its key feature is that the pressure-sensing part does not detect pressure through traditional pressure inlets; a flat sensing surface eliminates dead zones, prevents media residue, and also prevents clogging.

Having understood these, you also need to know the contacts of pressure switches. The most commonly used ones are normally open and normally closed relays with PNP output.

Relays have passive contacts that are not polarized. The two wires can be connected arbitrarily, and you can choose between normally open or normally closed contacts.

PNP output – This is an active output with polarity. It outputs 24VDC when the switch is activated and 0V when the switch is deactivated. It can be directly connected to the coil of an intermediate relay.

Pressure switch user manual:

Install:

1. Please adhere to the tightening torque.

2. When using the panel mounting connector for installation, do not apply excessive stress to the pressure switch/sensor controller.

3. Please do not drop, hit, or subject to impact.

4. When using a commercially available switching power supply, please ground the FG terminal.

5. Do not forcefully stretch the lead wire or pull the lead wire up the product body (tensile strength within 49N).

6. If there is a possibility of impurities in the fluid, please install a filter and separator on the primary side (inflow side) and install piping.

Wiring:

1. Do not pull the wire forcefully. Especially when assembling pipe fittings and piping, do not handle the pressure switch wire by hand.

2. Do not repeatedly bend or stretch the wire, bear heavy objects, or apply force.

3. Do not use the same wiring path as power lines and high-voltage lines.

4. Please check the insulation of the wiring.

5. When using analog output, please add an electrical noise filter between this product and the switching power supply.

Pressure switch precautions:

1. Determining the setpoint and pressure range: The recommended setpoint range is between 30% and 65% of the pressure range, and the optional setpoint range is between 15% and 90% of the pressure range.

2. Connection type: adjustable or fixed.

3. Is there pulsation? If the pressure pulsates or vibrates, a throttle valve is required to suppress the damage of the pulsating pressure to the instrument.

4. Applications with diaphragms: When measuring corrosiveness, high viscosity, or excessively high temperature, diaphragms are required.

5. Necessity of explosion protection: Explosion protection is divided into flameproof and intrinsically safe types, and most Nagano products are flameproof.

6. Do you need to bring instructions? As per customer instructions.

7. Number of contacts: One contact (one output) or two contacts (two outputs).