24V vs 10V for 4-20 ma signal for analog input module

Skiroy

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Join Date
Mar 2012
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Panama City,fl
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Hey guys were having difficulties with a flow meter that takes 24VDC PSU but sends 4-20ma output as we verified. The Compact Logix analog module says its +/- 10VDC but can see Voltage or 4-20ma. Our raw data is incorrect. When we use a 1VDC 4-20ma signal generator its raw data is as expected.

Is there a difference between 24VDC 4-20ma and 10VDC 4-20ma? Isnt 4-20ma, 4-20ma? No matter the voltage being used to the device? I could understand if we were reading voltage but not current.

It is a ABB 1769-IF4 analog module. And can anyone explain when and why would one use the the analog common on the module vs the -V/I terminal?
 
Skiroy,
I think you are getting bogged down with some unnecessary details. The 1769-IF4 can use -10 to +10VDC, 0-5VDC or 4-20mA signals. How you wire it and program it will determine how it works. In your case you want 4-20mA so dont worry about any of the other ways to use the module.

The meter that is sending the 4-20mA signal, is it sourcing or sinking? Sourcing means that the power for the 4-20mA look comes from the meters electronics. Sinking means that you will have to supply the power for the 4-20mA loop. Most of the flow meters I have used come set up to source the output. You may have to change a jumper or it could be a setting in the meters program.

Once you know how this is done if you look at page 2-20 (44 in the pdf) in the user manual for the wiring look at the top one for how you would wire it up.

Come back if you have more questions.
 
Skiroy,

A 4-20 ma loop will use anywhere from 10 to 32 volts dc in order to create the 4-20 ma signal.

A +/- 10 volt analog input is only concerned with the voltage and the current is really not that important.

I looked at the wiring diagram and it appears that you have the 4-20 ma signal going into the voltage input and not the current input.

There may also be a configuration file for the card that you have not done or set up correctly.

james
 
Skiroy,
I think you are getting bogged down with some unnecessary details. The 1769-IF4 can use -10 to +10VDC, 0-5VDC or 4-20mA signals. How you wire it and program it will determine how it works. In your case you want 4-20mA so dont worry about any of the other ways to use the module.

The meter that is sending the 4-20mA signal, is it sourcing or sinking? Sourcing means that the power for the 4-20mA look comes from the meters electronics. Sinking means that you will have to supply the power for the 4-20mA loop. Most of the flow meters I have used come set up to source the output. You may have to change a jumper or it could be a setting in the meters program.

Once you know how this is done if you look at page 2-20 (44 in the pdf) in the user manual for the wiring look at the top one for how you would wire it up.

Come back if you have more questions.
It must be sinking because we have to supply 120VAC to the metter to power the meter,but we also have to send a 24VDC source to the analog output section of the meter which it states is an active output. So we have a 24VDC PSU in which the 0v is tied to the V/I- and then the 24VDC+ side of the PSU goes into the meter passes out via terminal 16 and then goes into the Analog module at I+.

When we use a meter on the Flow meter out put we get 4-20ma at low and high range as expected but its raw data is not right in the PLC program,opposed to our signal generator at 1V tool in which it works fine.

So your saying look for a jumper to switch from source to sink correct? And though the module says -/+ 10VDC that it doesnt care if the 4-20ma signal is based from a 24vdc Power Device?
 
It must be sinking because we have to supply 120VAC to the metter to power the meter,but we also have to send a 24VDC source to the analog output section of the meter which it states is an active output. So we have a 24VDC PSU in which the 0v is tied to the V/I- and then the 24VDC+ side of the PSU goes into the meter passes out via terminal 16 and then goes into the Analog module at I+

You are correct if it is a Sinking output. You said it is an ACTIVE output which is the same as a SOURCING output. Active and Passive is the same as Sinking and Sourcing. I would look into that more. With no wires on the terminals can you measure any voltage between the output + and - terminals? You could be putting voltage on terminals that already have power. Also you need to connect the - side of your power supply to the ALG COM terminals. They might be jumper-ed together but that is way the manual shows it.

When we use a meter on the Flow meter out put we get 4-20ma at low and high range as expected but its raw data is not right in the PLC program,opposed to our signal generator at 1V tool in which it works fine.

So you are saying that if you put a 4-20mA source on the wires to the PLC you get good numbers in the PLC? Not sure I follow you here.

So your saying look for a jumper to switch from source to sink correct?

There is no jumper for selecting source or sink. The module will not provide any power out for the loop. It is a sink only. The field device or an external power supply must provide the power.

And though the module says -/+ 10VDC that it doesnt care if the 4-20ma signal is based from a 24vdc Power Device?

Yes how you wire the module will determine what signal it uses. If you look at the terminals there are more than one point to land wires per channel. Where you land your wires determines if the module is looking for a Current or a Voltage input.
 
Yes how you wire the module will determine what signal it uses. If you look at the terminals there are more than one point to land wires per channel. Where you land your wires determines if the module is looking for a Current or a Voltage input.[/quote]

Right Im wired to current input on module. But what Im asking is if the ABB Analog module documentation says the iput ranges can be +/- 10VDC or 4-20ma does it matter if the flow meter out puts 4-20ma but is a 24VDC device? In other words If I read voltage off the meters its 24VDC but the current is 4-20Ma. So if the ABB analog module wants to see 4-20ma its irrelevant if the flowmeter is a 10 or 24VDC device as long as its outputing 4-20ma and Im wired to the current input terminals on the ABB analog module,correct?

We did get it to work with jumping the analog common to the I- terminal,but we dont understand it? Can u ellaborate on this theory? I have wired pots and other analog devices without having to jumper to the analog common terminal. The documentation doesnt explain why this is. What is the use of this terminal?
 
The module only cares about the 4-20mA signal if that is what you are using. Like James said earlier, the voltage used to create a 4-20mA signal is normally 10-32VDC. 24 is the "normal" voltage used in industrial controls. So to answer your question yes you are correct in your thinking.

As for the I- terminal, take a look at the attached snip out of the IF4 manual. It shows that the I- and COM terminals need to be jumped together. That is most likely required due to how they built the electronics. With all electronic circuits you have to have a return path to ground. The 4-20mA circuit is no different. Power is sent out of the supply and goes through the meters output. The meters output "regulates" the current to between 4 and 20 mA and that "flows" back to the module. That power enters the module and in order for the module to know what the signal level is it must complete the circuit to ground. So by connecting the power supply ground to COM the module can complete the circuit and provide the numbers to the Processor.

IF4_snip.PNG
 
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Are all analog Com terminals jumpered internally because this diagrams only shows the 0vDC from the power supply going into the last terminal,then all the remaining ANLG Com terminals are used to jumper to the V/I- terminals?
 
Okay this is how I have typically wired a Pot to a AB Analog module and have never had to use the ANLG Com terminal. Why is this? Have I been doing it wrong?

pot.jpg
 
The way you have wired it in post #11 is a differential input. No jumper required. See pdf

The jumper is required for single-ended input wiring see post #9. The jumper provides a path to the power supply.
 
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The way you have wired it in post #11 is a differential input. No jumper required. See pdf

The jumper is required for single-ended input wiring see post #9. The jumper provides a path to the power supply.
Im not seeing the difference between my Pot wiring diagram and the Voltage Differential transmitter wiring in post #9? The only difference is the jumper that I never used.

Maybe I am looking at it wrong but a POT has a High(+),Low(0V) and the signal wire. The Voltage Differential Transmitter in Post #9 also has a High(+),Low(0V) and the signal wire.

So why does it need the jumper?
 
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The drawing in post #9 does not show a differential input its all single-ended.

Differential voltage input would be connected to Vin3+ and V/I in3- only, no connection to the common.
Differential current would be connected to V/I in3- and I in3+

Single-ended requires all commons tied together.

https://www.google.com/?gws_rd=ssl#q=differential+input+vs+single+ended
 
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