To explain in simple terms the relationship between sensors, transmitters, and pressure switches: Sensors are devices that detect physical properties such as pressure, temperature, or humidity and convert them into signals. Transmitters take these signals from sensors and convert them into a standardized output, often for long-distance transmission. Pressure switches, on the other hand, are devices that monitor pressure levels and can trigger an action (like turning on or off a device) when a certain pressure threshold is reached. In summary, sensors gather data, transmitters relay that data, and pressure switches act based on the data.

Over the years, the terms sensor, transmitter, and pressure switch have become confusing, as they are often used interchangeably and indiscriminately by different suppliers. The terms sensor and transmitter have been around for a long time, but the term transmitter is not very old in the field of process control. In particular, the term 'sensor' is widely used as the name for many devices and instruments. If you search the web for the terms sensor and transmitter, you will find many different definitions. Many organizations have their own definitions. To better help everyone distinguish between the three, the technical editor from Shaanxi Huibo Electromechanical willexplain the relationship between sensors, transmitters, and pressure switches in simple terms.Okay.
1) What is a sensor?

A sensor is a device or component that performs an initial measurement when sensing changes in physical variables.
A sensor is a device that makes physical contact with the measured variable, detects changes, and provides a measurable corresponding output signal.
2) What is a transmitter?
Well... let's talk about the term transmitter, as it has multiple definitions.
The term in process control may be borrowed from the telecommunications world, where a transmitter is a device that generates and transmits radio waves radiated from an antenna. These radio waves are ultimately detected and demodulated by a radio receiver. The receiver produces sound waves for the human ear.
In the field of process control, a transmitter is a device that transmits standard instrument signals that represent the measured physical variable.
The standard electrical signals are 1-5 V or 4-20 mA, representing 0-100% of the measured physical variable. This transmission signal is detected by a receiver, such as an analog input on a PLC or DCS.

So... we just said that the transmitter signal represents the physical variable. How does the transmitter know what the physical variable is?
This is where the sensor or transducer comes in. The sensor performs the initial measurement. If necessary, the sensor converts this initial measurement into an electrical signal, which is then amplified and standardized by the transmitter.
Here's an example... we are measuring process pressure in the range of 0-100 psi. Our sensor/transducer performs the initial measurement and converts it into a 0-3 mV electrical signal. The transmitter then converts that signal into a standard signal of 1-5 V, which is received by the PLC's analog input module.
Many suppliers use the terms pressure transmitter and pressure sensor interchangeably. But we now know that these two devices are different. So... buyers need to be careful...
3) What is a pressure switch?
Let's talk about pressure switches. A pressure switch is a two-part device consisting of a sensing sensor and an electrical switch.

Is there a difference between a pressure switch and a pressure transmitter?
There are some common components, but they are functionally very different. A pressure switch has a sensor just like a pressure transmitter. That's where the similarity ends.

As we have discussed, a pressure transmitter generates an analog voltage or current signal that represents 0-100% of the physical process pressure. A pressure switch has electrical contacts that open and close at a specific pressure.

Can a pressure transmitter be used as a pressure switch? The answer is yes, but is it really worth it?
First, pressure transmitters are larger, more expensive, and generally more difficult to install. There are other deterrents as well.

A practical example
Let's illustrate with an example... here we have a process control system where we need to open a valve when the pressure in the pipeline reaches 50 psi. We can use a calibrated pressure transmitter to produce a 4-20 mA output in the 0-100 psi pressure range.

We need an analog input module on our PLC, and we need to scale the analog module and insert code into the PLC program so that the 50 psi value triggers the event to open the valve.

Using a pressure switch connected to a simple PLC digital input module is much easier. The PLC valve control logic is also much simpler.

Most importantly, if you do not need to know the exact pressure but only need to know when a specific pressure point is below or above a set value, then stick with a pressure switch.
Okay... let's summarize what we have discussed...
- A transducer is a device that converts one form of energy into another.
- A sensor is a device or component that performs the initial measurement of a physical variable.
- All transducers are sensors, but not all sensors are transducers.
- All pressure sensors, pressure switches, and pressure transmitters must have a sensing sensor.
- A pressure switch consists of a sensor and an electrical switch that can open or close contacts at a specific pressure.
- A pressure transmitter is a device that converts the electrical signal from a transducer into a larger electrical signal.