How do I choose a 4-20mA transmitter? What is the difference between a 2, 3, or 4-wire transmitter and when should I use each?
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Choosing a 2, 3, or 4-wire transmitter depends on how accessible a power supply is to the transmitter, and what type of signal your source is. You can choose to build a discrete 4-20mA transmitter, or use a partially or fully integrated 2-wire or 3-wire transmitter from TI. Make sure to read the FAQs for:
2-wire transmitters are loop powered devices most commonly used to monitor a remote process with no access to a local supply. The sensor is powered by the transmitter. The transmitter and sensor must consume less than 4mA. If your system requires more than this, you may need to use a 3 or 4-wire transmitter. The sensor ground cannot be connected to the loop supply ground.
TI has the following 2-wire 4-20mA transmitters:
3-wire transmitters can be used with a local supply to transmit control data to remote devices. The ground of a 3-wire transmitter is shared with the receiver. Because 3-wire transmitters have a local supply, the sensor and its conditioning circuitry can consume more than 4mA. This allows 3-wire transmitters to use other common output current ranges such as 0-20mA or 0-24mA.
TI has the following 3-wire 4-20mA transmitters:
4-wire transmitters have separate paths for the power current and signal current, and the receiver does not share a common ground with the transmitter supply. Similar to 3-wire transmitters, 4-wire transmitters can also use other output current ranges such as 0-20mA or 0-24mA.
TI also offers 4-20mA transmitters that provide sensor excitation and signal conditioning