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porky2009
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PLC 4-20mA Output

04/27/2012 3:08 AM

Hi all.

In a PLC analogue output, how does the PLC vary the 4 - 20mA. The voltage is constant 24 Vdc...
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Del the cat
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Re: PLC 4-20mA output

04/27/2012 3:36 AM

It can't until a load is connected and then it will use current sensing and feedback to control the current (probably by adjusting the voltage).
I suspect you are measuring it off load.

Del

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Gord Graham
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#2

Re: PLC 4-20mA Output

04/27/2012 7:55 PM

A PLC can only work with digital number and to convert a 4-20 Ma signal for a PLC you install a 100 Ohm precision resistor across the two 4-20 ma wires. This will convert the 4-20 ma signal to a 1-5 vdc signal. The 1-5 signal is proportional to the 4-20 Ma signal
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Iris
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#3

Re: PLC 4-20mA Output

04/27/2012 9:21 PM

250 ohms to get 1-5 volts, not 100 ohms.
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Phys
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#4

Re: PLC 4-20mA Output

04/30/2012 8:50 AM

Timing is everything - just got an email from EDN.com that has an article on how to build a circuit to convert 1 to 5 v signal to a 4 to 20ma output - if you understand electronics, the circuit explains everything.

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