Hello everybody

How far WE can USE HART? 2Km? 120km?

 

3Km maximum.

Here's a link to a table from a whitepaper, 00840-0100-4075, Rev AA, by Emerson/Rosemount.

http://s32.postimg.org/vd581fz11/Emerson_HART_cable_guidelines.jpg

Since they invented HART, they're probably in a good position to make the statement.

 

The HART specification HCF_SPEC-054 says "at least 1500 m" (5000 ft). This is provided that good quality low capacitance and large cross section cable is used. There is a 65 microsecond rule and some diagrams in the standard illustrating this. Most plants require minimum AWG 18 (0.75 mm2) cable anyway. You can easily find PE insulated cable with capacitance of 60 nF/km which is great.

Cheers,
Jonas

 

Jonas. Can I use Ethernet cable for RS485 comm in distances of 150 meters? I have done it before with no problems. Is there any potential harm of doing this?

 

Yes, but if you want reassurance B&B Electronics publishes the distance vs the baud rate chart for RS-485 communications, assuming 24AWG twisted pair cable (CAT 5 cable) and a balanced interface (RS-485).

https://s17.postimg.org/cx0cgy0z3/cable_length_vs_data_rate_for_24_AWG_twisted_pair.jpg

As long as you stay below 300Kbits/sec the chart says you're OK.