Level & flow transmitter 500m from PLC

deelaluna

Member
Join Date
Feb 2008
Location
BALIKPAPAN
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Dear all,

I need your help, I'm still junior in automation field
I have 1 level transmitter & 3 flow meter which around 500mtr far from PLC AI/AO module,

1. Is it possible for me to use hardwire connection? is there any tips or tricks? what is the effect to the 4-20mA signal?

2. is there any devices or product which able to maintain 4-20mA accuracy ?


Thank you for the help,

regards,
 
Might be possible, I have transmitters 300 meters away. You will need to know the maximum impedance the transmitters can tolerate. Then calculate the impedance of your wiring and I/O card. If within the tolerance of the transmitter you should have no problems.

For example if your I/O card has an impedance of 250 ohms, and your wire 500 ohms and your device can tolerate upto 1000 ohms you are okay. However, if your device is only rated for 500 ohms, then it will not work. It you are close, increasing the wire size may be the answer.

So the first thing to check is the transmitter specification.


Ken
 
deelaluna said:
Dear all,

I need your help, I'm still junior in automation field
I have 1 level transmitter & 3 flow meter which around 500mtr far from PLC AI/AO module,

1. Is it possible for me to use hardwire connection? is there any tips or tricks? what is the effect to the 4-20mA signal?

2. is there any devices or product which able to maintain 4-20mA accuracy ?


Thank you for the help,

regards,
First, are the sensors loop powered (2 wire) or have their own power source (4 wire)?
For each sensor what is the maximum load impedance (resistance in ohms)?
If loop powered what will be the power supply voltage?
What wire gauge is going to be used?
What is the PLC AI module input impedance?
Are there any other devices in the 4-20ma loop?

Each sensor has a maximum load impedance it will power, typically 600 ohms but could be much more (1200 ohms) or less (300 ohms). If you add up all the series resistance (AI card,wire,recorder if used,external meter) you should be able to figure out if the loop will be OK. The load needs to be less than maximum the sensor will power.
Use at least a 24vdc power supply, if loop powered, and large gauge wire. You probably will be OK. Since it is a loop the current signal will be the same through out the loop. It is simple DC circuit.
An option is to have a remote I/O rack near the sensors and just one communication cable to the PLC. You might check the costs of both ways.
 

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