Transmitter
According to the basic DIN 1319 standard , a transmitter is a measuring device ( measuring device , measuring device , standard , ...) that converts an input variable into an output variable according to a fixed relationship. Measuring transducers are essential in all areas of technology, especially in automation , control and regulation technology.
Terms
The English term transmitter is also often used. The full term measuring transmitter is rarely used. Instead one speaks of a pressure transmitter or level transmitter.
Transmitters are also used
- Called a transducer if they have the same physical size at the input and output and work without auxiliary power, e.g. B. Current transformers that convert alternating current into alternating current;
- These are called measuring amplifiers if they have the same physical size at the input and output, but work with auxiliary power;
- Called a measurement converter if they convert into a different signal structure; here may measurement signals comprise an analog or digital signal structure, optionally also different digitally encoded structures. For the delimitation and explanation of analog and digital signals, see under digital measurement technology .
In some areas Transmitters are as sensors or short donors designated.
description
In the following, only those measuring transducers are shown that have an analog signal structure with different sizes in the input and output . Both electronic and non-electronic measuring devices can be used as such measuring devices.
The input signal of a transmitter is a physically measurable quantity . The part of the measuring device that responds directly to the measured variable is called the measured variable transducer, sensor (according to DIN 1319) or measuring probe. Processable variables are generated in the sensor by means of physical or chemical effects, mainly in the form of electrical signals. A standardized analog electrical standard signal is often generated as the output signal . Amplification and linearization are often necessary as intermediate steps. For simple applications, a Boolean variable is sufficient at the output (e.g. switching output for reference potential ).
A standardized analog electrical standard signal is often available as the output signal:
- 0… 20 mA
- 4… 20 mA (preferred; see also standard signal )
- 0… 10 V
- 10 ... 90% (0.5 V ... 4.5 V at = 5 V, ratiometric output signal)
Measuring transducers for electrical input variables often offer galvanic separation of the measured and output variables.
There are also transducers with the output signals time or frequency. There are two reasons for using them:
- These quantities can be recorded digitally very easily by means of limited counting with counters .
- These variables require a carrier (voltage or current) whose signal level does not contain any information, so that interference can hardly falsify the information.
A voltage-time converter is used in the analog processing stage of a digital voltage measuring device according to the two-ramp method .
A voltage-frequency converter is used in the analog processing stage of a digital voltage measuring device according to the charge balance method .
Examples
Transmitters are widely used to evaluate the following physical quantities:
- temperature
- rotational speed
- Rotation angle
- length
- pressure
- force
- strain
- electrical voltage
- electric current
- electrical power
- Flow
- Humidity
- Level
- frequency
- Components of gases ( gas sensor )
A pneumatic output signal was previously used to use transmitters in potentially explosive areas when there was no way to safely use electrical components in an explosive environment.
Example of a practical application
A mining company sells natural gas to a gas company. There is a pipeline for transport. A measuring orifice is installed at the transfer point. The differential pressure at the orifice creates a membrane deformation, this is recorded electrically and converted into a standard signal of 4… 20 mA. This signal is fed to the process computer in a control room. There, the current flow rate and the quantity delivered over time are calculated from this signal. The flow is the basis for the process control; the amount is the basis for commercial accounting. The measuring point is called a flow transmitter or a flow transmitter.