4-20mA Current Transmitter

[morizabal]

Aside from electrical connections what are the differences between a 3 wire current trasmitter and a 2 wire system. Which one is preferred in industry? Is it dependent on application?

 

[larryg]

Morizabal,
If I recall correctly, a two wire transmitter requires excitation voltage from the device it is connected to. A three-wire transmitter allows you to use an external supply (typically 15-30VDC).

Some PLC's provide power for your transmitters and some don't. As for preference, if you can do without the extra external power supplies, you can save on cost. Also, if you use the PLC's power, you minimize noise issues.

Hope that helps.

LarryG

 

[jbartos]

Suggestion:
1. There may be a tradition factor. 4-20ma has been widely used. It is linked to two-terminal devices.
2. Smart sensors may be more demanding on power supply and consuming more; therefore, the power supply is needed. Also, various nice features such as communications, alarms, selfdiagnosis, memory retention, etc. need power supply.
3. Three-wire loops are going to stay and will be progressing.
4. There are now projects that are overcrowded with power supplies.