Transmitter Explained - Types of TransmittersIn this article, we’re going to introduce you to a very important device used in process control today.
In this article, we’re going to introduce you to a very important device used in process control today – the Transmitter.
First of all, let’s talk about the term transmitter because it has more than one definition.
In the Telecommunications world, a Transmitter is a device that produces radio waves radiating from an antenna.
In the world of process control, a Transmitter is a device that converts the signal produced by a sensor into a standard instrumentation signal representing a process variable being measured and controlled.
Pneumatic vs electrical signal
In the early days of process control, the standard instrumentation signal was pneumatic while today it is more likely to be an electrical signal.
The standard pneumatic signal is 3 to 15 psi.
The standard electrical signals are 1 to 5 volts or 4 to 20 mA.
And just to add a bit more confusion to the term Transmitter, some people in the industrial instrumentation field will tell you that a Transducer and a Transmitter are the same things and therefore the terms are interchangeable.
As mentioned earlier, the electrical transmitter output signal is usually a range of voltage (1 to 5V) or current (4 to 20 mA).
In process control, it is understood and goes without saying that the transmitter output range represents the 0 to 100% of the sensed physical variable.
For example, the transmitter would produce an output current range of 4 to 20 mA for a measured temperature range of 0 to 150 degrees Fahrenheit (0 to 100%).
We’ve talked a lot about the transmitter and the sensor. Let’s have a look at where the transmitter fits into a process control loop.
As already stated, the Transmitter converts the signal from the sensor to the Process Variable (PV) signal which represents the physical measured variable.
The Controller is the device that looks at the difference between the Process Variable (PV) and the Set-point (SP).
The Controller then determines what action to take place and generates an output signal that is a function of the result of this comparison. Controllers are either a DCS or a PLC in process control today.
The Final Actuator is the device such as a valve that exerts a direct influence on the process as directed by the controller.
Variables measured by the transmitter
The four major process variables measured and represented by a transmitter are Pressure, Level, Temperature, and Flow.
Transmitters are also used in industry to measure other variables such as Position and Speed and chemical properties such as pH and Conductivity.
4-wire and 2-wire transmitters
A Transmitter requires a power supply to operate as discussed in our article “What are 2-Wire and 4-Wire Transmitter Output Loops?”
Let’s review quickly… A 4-wire transmitter has 2 wires connected to a power supply and 2 signal wires connected to the PLC. The power supply can be AC or DC depending on the vendor and model.
A 2-wire transmitter has only 2 wires. These 2 wires provide power for the transmitter and are also the signal lines!
New technologies have spawned the development of Smart Transmitters.
Smart Transmitters not only produce the 4 to 20 mA process variable signal, but also transmit and receive digital information such as Instrument Tag Names, Calibration Data, and Sensor Diagnostics. Protocols such as HART are commonly used on Smart Transmitters.
Ok, let’s review…
– In the Telecommunications world, a Transmitter is a device that produces radio waves radiating from an antenna.
– A Transmitter in process control is a device that converts the signal produced by a sensor into a standard instrumentation signal representing a process variable being measured and controlled.
– The transmitter standard pneumatic signal is 3 to 15 psi.
– In instrumentation, the terms Transducer and Transmitter are quite often used to name the same device.
– The four major variables measured and represented by a transmitter are Pressure, Level, Temperature, and Flow.
– Instrumentation Transmitters can be connected in a 4-wire or 2-wire configuration.
You might want to review two of our other articles:
Want to Learn More?
Newcomers to RealPars have free access to one of our online courses.
You can take advantage of this offer by downloading the RealPars app (iOS, Apple TV, Android, Android TV, FireTV, Roku) and selecting the first lesson of the PLC Hardware course. Just like the video, the lessons are all high-quality and also very easy-to-follow.
Also, for a low monthly fee, you’ll get full access to an exclusive library of courses on PLC programming and industrial automation topics as well as new fresh out of the oven videos each and every week. These courses are all member-exclusive and are not shared anywhere else on the internet.
If you would like to get additional training on a similar subject please let us know in the comment section.
Check back with us soon for more automation control topics.
Got a friend, client, or colleague who could use some of this information? Please share this article.
In this blog post, you’ll learn about the mindset that helped me getting a PLC programming job with NO experience. This is my personal experience as someone who searched for a job in this field and as an employer who reviews resumes and interviews candidates for a variety of projects. So let’s get started!
In this article, we’re going to discuss a very common flow measuring device called a Turbine Flow Meter.Depending on who you talk to, a Turbine Meter has one or two major parts. Some will tell you that the Turbine Meter has only one part: the Mechanical component....
In this article, we're going to talk about Sinking and Sourcing PLC digital output modules and how they connect to field devices.As we’ve discussed in our other articles, the two types of PLC output modules are Digital and Analog. Drilling down even further, Digital...
Learn how to program PLCs, install and wire industrial devices, and at the same time purchase them online.
+31 10 316 6400
Mon - Fri 8:30 am to 5:30 pm (CET)
Rotterdam Science Tower, Marconistraat 16,
3029AK Rotterdam, Netherlands
© 2021 RealPars B.V. All rights reserved.
Created with coffee and tea in Rotterdam.