Current transducers convert AC or DC electrical current signals into analog instrumentation signals for industrial control systems. They are important for running high-power machinery and processes. Transducers convert electrical energy into other forms of energy and are used in audio speakers and pressure transducers. Current transducers were extensively used in computerized process plants in the 1970s and 1980s. They are also used to convert 4-20mA DC analog process signals to 3-15psi analog pneumatic signals and to operate proportional pneumatic control valves. Sensor-specific transducers measure the magnetic flux of a power conductor to sense drive motor currents for machinery and process equipment.
A current transducer is a device that converts AC or DC electrical current signals into analog instrumentation signals so that they can be used and easily interpreted by certain industrial control systems. Most of the time they don’t look like much from the outside; they are usually square or rectangular in shape and might look like a portable speaker with input and output cable jacks. However, their function is very important for a number of different mechanical operations. Electricity is essential for running many types of high-power machinery and processes in manufacturing and other industrial settings. However, simply plugging machines into outlets isn’t always the best solution, which is where transducers come into play. The device takes the raw energy from the source and converts it exactly into the nominal values required by the machine on the input side. The engineering behind how this process occurs can be quite complex, but the simple fact of how it works is the most important aspect in most cases.
Transducers in general
In general, the term “transducer” is used for any device or mechanism that converts electrical energy into other forms of energy. Transducers are commonly a part of audio speakers, for example, converting electrical energy into audio energy; in pressure transducers, they convert to electrical signaling. The combined term “current transducer,” however, is usually only used in settings that require the conversion of alternating current (AC) or direct current (DC) electrical current signals to an analog signal basis. Convert the measured AC or DC current value, perhaps the power of a motor or pump, to a 4-20 mA (mA) DC analog process value or a 3-15 psi pneumatic signal for systems of pneumatic control. These devices usually appear to run on normal electricity, but the transducer is regulating the energy and output.
Main uses
Current transducers were used extensively in the 1970s and 1980s as large process plants, such as oil refineries, became computerized. Most had been controlled by pneumatic control systems up to that point, due to the inherent safety of pneumatics in flammable and explosive environments. In order for computers to use the real-time information from the many process pneumatic transmitters that measure temperatures, pressures, flows, levels and other variables, their pneumatic outputs must be converted into electronic signals using pressure.
There were also hundreds of air-operated control valves in these plants that had to get their output instructions from the control computer. In most cases, those computers sent signals such as 4-20mA DC analog current signals. This required a conversion from current to pneumatics. The industry soon referred to them as I to P or I/P transducers, with the “I” denoting current input and the “P” denoting pneumatic output.
Importance of magnetic fields
Most I/P transducers convert their electronic signals to pneumatics by passing current through a coil wound in a magnetic field, which modulates a back pressure nozzle into a pneumatic pilot circuit providing 3-15 psi pneumatic output . Pressure-to-current devices use pressure diaphragms mechanically linked to excited strain gauges, piezoelectric sensors, or capacitance sensors that drive one section of the output amplifier. These then transmit the required 4-20mA DC current output to the control systems.
Conversion devices
Relevant to the controls industry, the term is also used to refer to specific converter devices. These devices change 4-20mA DC analog process signals to 3-15psi analog pneumatic signals to operate proportional pneumatic control valves or to convert pressure signals to proportional 4-20mA DC analog process signals. These measurements are typically used to describe a process that is functioning normally. By converting an instrument’s actual signals into these standardized ranges, measurements outside these ranges can be annotated and used in diagnostics.
Sensor specific transducers
Some types of sensors, usually those that measure the magnetic flux of a power conductor to sense drive motor currents for machinery and process equipment, may also carry the name of the current transducer. These usually involve the transmission of an analog milliampere or voltage signal to control systems.
Solid core transducers have closed loop transformers that must be slipped onto the temporarily open end of a power conductor. Split core transducers, on the other hand, have a hinged side of the transformer ring that can be temporarily opened to allow the ring to slide around a conductor that cannot be disconnected. They usually incorporate rectifier and adjustable output conditioning circuits to allow specific calibrations for analog control systems.
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