Belden 3078F

[esung911]

Hi,

Has anyone done any banchmarks to compare Belden 3078F versus the 3076F or recommend it? How much more signal degradation would I get from using a 3076F than a 3078F?

This reminds me of shopping for stereo wiring, gold plated or platinum....:confused:

Thanks

[IanVerhappen]

Though not a cabling expert by any means, the good news is that the Foundation is developing a cable specification against which you will be able to get a "check mark" just like field devices, the bad news is that I don't know when it will be available.

More news, is that there are other suppliers besides Belden who manufacture FF cable, Kerpen and Northwire are two that I am familiar with so check out their web sites to learn more about the various options and what they mean.

Ian Verhappen

[marisg]

Fieldbus requires that the cable's characteristic impedance be 100 Ohms. The 3078 cable has 150 Ohm characteristic impedance. If you are trying to save a little money by going to a lower wire size, try the 3077F cable, but be aware that you will get a lot more voltage drop feeding power to fieldbus devices in the field. Unless your cable runs are very short, I would not recommend that approach.

[aagostin]

Since you are posting this on the fieldbus forum, I assume you are looking for cable for Foundation Fieldbus H1, 32.25kBit/s. In that case, there is a specification that specifies the parameters that can be used with FF. As such, the cable manufacturers will clearly indicate whether a cable is produced according to this specification, and will then label it accordingly.
The 3078F is a fieldbus cable, but for high speed (1MBit/s to 2.5MBit/s). As such, as Maris wrote, it has an impedance of 150Ohm/km +/- 10% according to the IEC61158-2 fieldbus standard. Note that this standard not only specifies FF H1 but other bus systems as well. Hence the fine print in the datasheets becomes important.
Cable manufacturers can probably offer other H1 cables with thinner diameters, but the ohmic resistance will increase so that the voltage drop will increase. Usually is the other way round: customers rather look for thicker cables to compensate for the voltage drop and then connect more devices at longer distances. I know there is a cost impact to go for thicker cables than AWG18, but I would not expect too much savings going for thinner cable, since the base costs of manufacturing are sitll there in addition to the costs of raw copper.

[esung911]

Thanks for everyone's input.