Current loops are useful for accurately communicating analog signals over long distances. Unlike voltage, current does not vary due to line resistance or capacitance—both which change with cable length. Current loops provide a high level of noise immunity. As a result, they are widely used in electrically noisy environments.
Maxim provides a wide range of products designed for implementing and protecting 4-20mA communication links.
Faulty current loop conditions as well as reverse inputs can easily damage sensor devices. Maxim's MAX14626, the industry's first 4-20mA current loop protector for industrial analog input modules, protects the sensor by restricting the amount of current with a current-limit switch. The device also prevents a reverse connection from damaging the sensor by isolating the output from the input with reverse-input protection.
See the MAX14626 data sheet for more information.
The MAX12900 is an ultra-low-power, highly integrated 4-20mA sensor transmitter in a small 5mm x 5mm package that converts PWM data from a microcontroller into current over a 4-20mA loop with two, three, or four-wire configurations.
See the MAX12900 data sheet for more information.
Analog signals from sensors need to be conditioned or prepared for further processing, e.g., for conversion from voltage to current. The MAX15500/MAX15501 analog output conditioners, acting as current loop transmitters, provide a programmable current up to ±24mA. These output conditioners also enhance system safety and reliability by protecting outputs against overcurrent conditions as well as a short-to-ground.
Highway Addressable Remote Transducer (HART®) technology allows a secondary (digital) signal to be superimposed on top of an analog signal using the 4-20mA current loop. The technology uses the current loop as the carrier and does not affect the loop's original analog communication capability. Maxim's DS8500 is one such HART modem that integrates modulation and demodulation.
See the DS8500 data sheet for more information.
The application notes referenced below provide a wealth of information on building current loop transmitters and loop-powered transceivers with integrated sensor interfaces.
|Reference Circuit||5610||High-Performance, High-Accuracy 4-20mA Current-Loop Transmitter Meets Toughest Industrial Requirements|
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