Hart protocol

[vikas1947]

can i connect a rtd transmitter which is working using HART protocol ...can i give input to micrologix series plc or does it require special type of input module for hart sensore??

 

[nonuke]

Yes you can. Hart works on a 4-20ma current loop.

 

[danw]

A regular 4-20mA input will handle the HART 4-20mA output as just a 4-20mA signal, but a regular 4-20mA input won't be abel to decode any of the additional HART data.

If there's some requirement to use a HART communicator (handheld or software) to configure the HART field instrument then those devices need at least 250 ohms in the loop circuit to be able to read the HART signal.

Sometimes an additional resistor is put in series in the circuit for those analog inputs that use 10 or 100 or 62.5 ohm resistors (or whatever) across the AI input for current signals. Others break the loop open, insert a temporary resistor to do what's needed when they have to use the HART communicator or HART modem, then put it back together when they're done.