Maximum Allowable Distance Between HART Transmitter and S7-300 AI HART Card

[m_sadeghinia]

Hi
I'm working on a project that a HART transmitters and related control system (Siemens S7-300 with HART analogue input module) are 1100 meter away from each other.
between these two, there's multi pair cable with below specification:
12x2x0.75+7x0.5, CU/PVCISCR/OSCR/PVC/LSh/PVC/SWA/PVC
Cables will be laid in concrete trench.
Can anyone tell me please that this distance would be a problem or not? and if it is, how can i solve this...
Thanks.

[carl_e]

Every 2 wire loop powered HART transmitter has a spec for how much voltage the power supply has to provide in order to overcome the total loop resistance.
Sometimes this is a chart of resistance vs voltage, as shown in the attachment.

[link Point to another website Only the registered members can access] Other times it's an equation.

You need to determine the resistance of the copper wire for the run (remember that 1100m distance is 2200m of wire) and add to that the input resistance of the HART analog input module (typically 250 ohms, but it varies from model to model, mfr to mfr.) Then check the chart for your transmitters and see if your power supply has enough voltage to make the grade. If not, increase wire size or boost the power supply voltage.

[m_sadeghinia]

Thanks dear Carl.
May i know the reference of the image you mentioned? Or hopefully it's download link?

[carl_e]

The graph is sometimes called a "load line".

Every series of devices (like a brand x pressure transmitter or brand y temperature transmitter has its own load line graph or equivalent equation. The one I posted is for a Siemens DSIII pressure transmitter (published in the manual not the catalog page or spec sheet), but you should really use a load line for the specific devices that your project deals with.

Although most pressure transmitters have nearly identical specs (~10.5 volts to turn on with zero resistance in the loop) there are other 2 wire loop powered field instruments that require 19V+ to turn on and initialize, which would function only with much less loop resistance than a pressure transmitter.

I forgot to mention that
- the resistance of an Intrinsic Safety barrier
- resistance of loop powered meters in the loop
need to be taken into account in the calculation.

The devil is in the details.