4-20mA Question

How far realisticly can i run a 4-20mA signal ?

I am looking at about 150 meters back to an NI16I card.....

I n theory you could run this farr as the moon. It all depends on the cct resistance.

The bigger the cable, the farther you'll go.

What to look at is the transmitter. It must be rated for a certain impedance.

150 meters is usually a piece of cake. I have runned this in the thousand of feet.

Say you run the loop on 24 Vdc and at the other end there is a 1-5 volts conversion going on in the input module. You'll need to have enough voltage left after the drop due to the cable lenth, to pull the 1-5 volts.

24 volts / 20 mA = 1.2 Kohm

The total loop resistance must not be over this or the x-mitter will not have the mean to push the signal through it.

What is the cable resistance ??? You must by now realise how far you can push the signal

Very farrrrr.

Pierre said:

I n theory you could run this farr as the moon.

Click to expand...

As long as you take into account that at that distance your data is about 2.6 seconds old.

many thanks boys

I thought it was the case (resistance wise)!

just wanted to check as all my signals are normally 1-10 meters max, on a project that has 8 x 150 mtr loops and didnt want to make a **** up !

Here is a discussion on a similar topic:
http://www.plctalk.net/qanda/showthread.php?s=&threadid=8504&highlight=wire+size

Personally Sounds like a good job for devicenet or control net or whatever communications flavor you like. With needing 8 channels of analog it may be cheaper to go that route. (cheaper as overall not just looking at hardware but also installation)

If there is other i/o then that is a real god possibility.

Drewcrew6