Glossary · Process instrumentation and analytical measurement
Two-wire transmitter
Also known as: 2-wire transmitter
German: Zweileiter-Messumformer
In process instrumentation, a two-wire transmitter is a transmitter that is connected with only two wires, which carry both its supply and its output signal; it regulates the loop current between 4 and 20 mA and operates on less than the 4 mA live zero.
- Process instrumentation
- Process industry
In one sentence
A two-wire transmitter uses one pair of wires for both power and its 4–20 mA signal, the standard wiring for process field instruments.
Example
Most pressure and temperature transmitters in a chemical plant are two-wire transmitters connected to analog input cards with HART.
How it applies
- Engineering: Two-wire wiring minimizes cabling and suits intrinsically safe circuits. The loop supply must provide the device's minimum terminal voltage at 20 mA or higher failure currents, plus all voltage drops in the loop.
- Commissioning: Loop checks verify wiring and scaling; HART communication allows configuration from the control system or a handheld.
- Troubleshooting: A signal that cannot rise above a certain value often indicates insufficient loop voltage or too much resistance, not a process limit.
- Documentation: Keep the loop diagrams and load calculation current. Use one term consistently: this site treats Two-wire transducer and Loop-powered transmitter as close synonyms.
Two-wire vs. four-wire transmitter
A two-wire transmitter is powered by the signal loop. A Four-wire transmitter has a separate supply and is used for devices that need more power.