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Pressure Transmitter

In this video we will explain the operation of the transmitter, a device used to convert physical quantities into readable data visualizations, a basic requirement in every technological field.

More than 10 years in industrial supplies sector have led JAES to become a qualified partner for some of the most important industrial automation companies, providing any kind of transmitters.

A transmitter is a device which converts the signal produced by a sensor and a transducer into a signal that can be read and interpreted by a controller.

At the beginning of process control the signal was pneumatic but today electronics have replaced almost all pneumatic controls and this is the reason why many modern transducers have an electronic output.

The standard pneumatic signal is from 3 to 15 PSI, an acronym that stands for “pound-force per square inch”, which in the international system corresponds to : from 20 to 100 kPa [kilopascal].
Instead, the standard electrical signals of a transmitter are a voltage range (typically from 0 to 5 Volts, and from 0 to 10 Volts) or a current range (usually from 4 to 20 milliamps).

The main measurements detected by a transmitter are usually physical variables such as: Temperature, Level, Flow and Pressure.

Consider, for example, a pipe that we want to monitor the pressure, this oscillates between 50 and 150 PSI, which we can approximate in the international system as 345 and 1035 kPa [kilopascal];
a transducer detects the pressure in the pipe through the sensor, in this case a diaphragm, and sends an analog electronic signal of a few millivolts to the transmitter.
The pressure transmitter (properly calibrated on the minimum and maximum pressure range) linearizes, Compensates and Boosts the signal, which in this case is a range between 4mA and 20mA [milliampere].
The signal is sent to the programmable logic controller (PLC), a computer that will interpret the electrical current at 20mA in a pipe pressure of 150 PSI or 1035 kPa | 4 mA in 50 PSI or 345 kPa | and for example 12 mA in 100 PSI or 690 kPa (that is 50% of the pressure range).
Now the controller can determine the pressure and, if necessary, modify it by sending a signal to the actuator that controls a pressure regulator.

In the international system, the unit of measurement for pressure is Pascal,
And it’s equivalent to 1 newton per square meter. In fact, the pressure is the ratio between the force in the direction orthogonal to the surface and the area of the contact surface.
Pascal is widely used together with its multiples, as hectopascal (hPa), or kilopascals (kPa) and it is named after Blaise Pascal, a French mathematician, physicist and philosopher who formulated Pascal’s Law.
If you are interested in how the pressure is employed in different machinery, check out our previous video on hydraulic and pneumatic cylinder operation.

A transmitter needs a power supply to work, which depending on the model can be direct current (DC) or alternating current (AC)

Furthermore, a transmitter can be in the 2-wire version, where the 2 power cables also act as signal lines, or even 4-wire version, where 2 cables are connected to a power supply and the other 2 send the signal to the controller.