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hi all,
i need to communicate from plc to flowmeter which is 400 meter distance. we are communication using 4-20ma so please advice me.

RE: communication

Something like this at both ends ? Link

RE: communication

4-20mA will easily run over 400m of shielded, twisted pair copper cable, assuming either an active output powered by the flowmeter or a passive output powered by a 24Vdc power supply. It's been done every day for the past 50 years. There are likely wireless solutions whose cost you can trade off against the cost of laying copper cable, depending on the landscape that the signal has to traverse.

4-20mA from flowmeters frequently uses HART for either setup, troubleshooting or multiple variables. HART functionality is lost when wireless or Fiber optic is used.

RE: communication

4-20 mA will work over much longer distances than 400 meters. You can consider increasing the wire size, but at 400 meters, it should be entirely feasible. Just look at total loop resistance and make sure the source is adequate.

RE: communication

If that was a lone signal from way across a field with frequent lightning storms you might want to do something different but if lightning isn't an issue in the area then only the wire size needs to be considered.

Keith Cress
kcress - http://www.flaminsystems.com

RE: communication

Can you use Zigbee with a mesh network... it's good to about 300m, by itself and can be extended much further, and I doubt that you would have a massive amount of data. It's very low power... much less than bluetooth or wi-fi...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?


RE: communication

some are saying that 4-20mA can take a maximum distance of 150 meter only.
if 4-20mA can take to 400 meter can you please suggest the cable size and best method.

RE: communication

They may be right, but are probably not. I've seen plenty of installations over 400 m with 4-20 mA working fine. To perform the calculation, you need to know the voltage of the 4-20 mA circuit power supply if loop powered or the maximum output voltage of the flowmeter if externally powered (or its max circuit resistance, if stated), along with the resistance of the input it's driving, e.g., 250 Ω or 500 Ω, and the resistance per unit length of the shielded twisted pair cable size you think you want to use. Here is a great reference that will help you do the calculation yourself: Link. Once you've done that, someone here can check your work.

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RE: communication

Whoever is saying 150 meters is a maximum length for 4-20 mA is misinformed. I once did an installation of a couple of kilometers, IIRC. We used #10 AWG shielded cable.

Possibly, some organization has recommended maximum of 150 meters, but this isn't based on physics, unless they were using extremely small wire, or had very limited power capacity in the loop power supply.

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