Transmitters, also called measuring transducers in German, play an important role in all areas of technology, but especially in control, regulation and automation technology. The article sheds light on what measuring transducers are, how signal transmission works and where measuring transducers are already used in industry.
In German measurement technology, transducers are often referred to by the English term "Transmitter". The term "measuring transmitter" is rarely used, but is more frequently used to refer to pressure transmitters or level transmitters.
According to DIN 1319, a transmitter is a measuring device – i.e. a device or special measuring equipment – which converts an input variable into an output variable.
Each transmitter therefore contains electronics for direct application in addition to its sensors. According to the standard, only the part of the measuring device that responds directly to the measurand is referred to as the sensor, measurand transducer or probe.
In other words, transmitters are measuring devices that measure process variables such as temperature or filling level and then convert the measured value into the standard signal. This process serves the purpose of ensuring that the respective process variable can be transmitted reliably. Processing can then be carried out by evaluation devices that have analog inputs. These are, for example, displays, process control systems, programmable logic controllers and controllers for building automation.
Measuring amplifiers are used as aids in measuring and sensor technology. These are used to measure voltages and currents that are below the response sensitivity of the respective measuring device. Measuring amplifiers convert the voltage to be measured into analog or digital output signals.
Nowadays, it is quite normal for technical systems to measure and display the values of all relevant process variables and to further process the respective operational information accordingly. However, this was not always the case, but is due to the general automation of plant technology. Thus, many more measuring devices are used today than just a few years ago.
An important step in this development was the introduction of transmitters. Today, transmitters are used in electrical engineering for a number of physically measurable quantities.
These are the following quantities:
One example of transmitters in electrical engineering is the measurement of the flow rate in gas pipelines. Producing companies that sell natural gas use special orifice plates at the transfer point to record how much gas is delivered over time. This is aided by the differential pressure at the orifice plate, which is also known as a flow transmitter or flow transducer. The pressure results in diaphragm deformation, which is detected electrically and converted into a standard signal in milliamperes (unit for amperage). The signal goes to the process computer in a control room, where it is used to calculate the current flow rate and the amount of gas delivered. The measurement of the flow rate is so important because the process control is based on it. In addition, the measured quantity of gas forms the basis for the commercial calculation.
A wide variety of physically measurable variables are suitable as input signals. Physical or chemical effects are used to generate quantities in the sensor or probe – usually in the form of electrical signals – which can be further processed. In most cases, the measured variable and the output variable are galvanically isolated.
The measurement signal is transmitted from the respective sensor to a transmitter. For example, the measurement signal for a temperature measurement consists of a thermoelectric voltage. This can be of the order of a few millivolts, for example. In the context of flow measurement, pressure signals are then transmitted which manifest themselves in the pipeline by means of the corresponding process fluid (for example nitric acid).
The transmitter thus serves the purpose of converting the input signal into an output signal which has the form of a standard signal. This is thus transmitted in electrical or pneumatic form.
Transmitters in industry generate an electrical standard signal as an output signal, usually a standardized analog signal. This is, for example, 0_20 or 4_20 milliamperes or 0_10 volts. However, the standard signal can also have a digital structure. Both are essential for the connection to various control units.
This process often involves intermediate steps such as amplification of the voltages and currents by means of a measuring amplifier or linearization. Transmitters are therefore essential and therefore the supply of industrial spare parts is particularly necessary.
According to the DIN 1319 standard, a transmitter is a measuring device that converts an input variable into an output variable. Measuring transducers are used in many areas of modern industry, especially in automation, control and regulation technology. The transducers thus transform physical and non-electrical quantities into electrical quantities. Examples include photodiodes and thermocouples, which translate solar radiation or temperature into voltage. The output variables converted by the signal converters are usually provided with standardized analog or digital values so that they can be easily connected to the respective control units. Transducers are used, among other things, in the evaluation of the physical variables temperature, speed, angle of rotation or length.
