Why choose 4~20mA standard current signal output?

Generally speaking, the current output-based our UPB1 pressure transmitter, UTB3 temperature transmitter and other products are commonly used in the industry with a two-wire 4-20mA output.

The design of 4-20mA two-wire sensor uses 20mA to represent the full scale of the signal.

The selection of the maximum current of 20mA is based on safety and practical considerations. The spark energy caused by the current on and off of 20mA is not enough to ignite the gas.

But why is the starting signal not 0mA?

The current type transmitter converts the physical quantity into a 4-20mA standard current signal output, which must be powered by an external power supply. The 0-4mA current is to supply the minimum working current of the sensor itself. If 0-20mA is used, when the signal is At a very young age, the sensor does not get enough energy to work.

When the signal is lower than 4mA and higher than 20mA, it is used for various fault alarms. For example, it will not be lower than 4mA during normal operation. When the transmission line is broken due to a fault, the loop current is reduced to 0, so 2mA is often taken as the disconnection. alarm value.

At the same time, the electrical zero point of the instrument is 4mA, which does not coincide with the mechanical zero point. This "live zero point" is conducive to identifying faults such as power failure and disconnection.

For more details, please contact Stella Meng.