In this article, we are going to introduce you to a very important device that is used in process control today.
First of all, let’s talk about the term transmitter because it has more than one definition. In the world of telecommunications, a transmitter is a device that generates radio waves emitted by an antenna.
In the world of process control, a transmitter is a device that shows the signal generated by a sensor to a standard instrument signal that measures and controls the process variable.
Pneumatic signal against electricity
In the early days of process control, signal was the standard pneumatic tool , while today it is most likely an electrical signal.
The standard pneumatic signal is 3 to 15 psi.
Standard electrical signals are 1 to 5 volts or 4 to 20 mA.
Just to make the term transmitter a little more confusing, some people in the field of industrial instrumentation will tell you that converters and transmitters are the same thing, so the terms are interchangeable. As mentioned earlier, the output signal of an electrical transmitter is usually in the range of voltage (1 to 5 volts) or current (4 to 20 mA). In process control, it is understandable, not to mention that the output range of the transmitter shows 0 to 100% of the sensed physical variable. For example, the transmitter produces an output current range of 4 to 20 mA for the measured temperature range of 0 to 150 degrees Fahrenheit (0 to 100).
We talked a lot about transmitters and sensors. Let’s look at how the transmitter fits into a process control loop. As mentioned earlier, the transmitter converts a signal from a sensor into a process variable (PV) signal that represents the physically measured variable. A controller is a device that examines the difference between a process variable (PV) and an adjustment point (SP).
The controller then determines what to do and generates an output signal that is a function of the result of this comparison. Today the controllers are either DCS or PLC in process control. The final actuator is a valve-like device that directly affects the process.
Variables measured by a transmitter
The four main process variables are measured and represented by a transmitter: 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 needs a power supply to operate, as in our article “What are 2-wire and 4-wire transmitter output loops?”
A 4-wire transmitter has 2 wires connected to the power supply and 2 signal wires connected to the PLC. Depending on the vendor and model, the power supply can be AC or DC. A 2-wire transmitter has only 2 wires. These 2 wires provide the power of the transmitter and are also signal lines!
New technologies have led to the development of smart transmitters.
Smart transmitters not only generate 4 to 20 mA variable signals, but also send and receive digital information such as instrument label names, calibration data and sensor detection. Protocols such as HART are commonly used in smart transmitters.
– In the world of telecommunications, a transmitter is a device that generates radio waves emitted by an antenna.
A process controller is a device that shows the signal generated by a sensor to a standard instrument signal that the process variable is being measured and controlled.
– The standard pneumatic signal of a transmitter is 3 to 15 psi.
In instrumentation, the terms converter and transmitter are often used to name a device.
– Four main variables are measured and represented by a transmitter: pressure , level, temperature and flow.
Instrument transmitters can be connected in a 4-wire or 2-wire configuration.
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