Wago Passive Isolator with Active AI

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Thread Starter

Hamid Ankuti

i have Wago 857-451 passive isolator and Analog Input Card Siemens 7kf02 that is active AI.

Can i connect this Wago to this AI?
and my transmitter must be 2 wire or 4 wire?
 
H

hamid Ankuti

who know what is my problem? please help me that my transmitter must will select 2 wire or 4 wire? can i connect 2 wire transmitter to Wago 857-451? and i don't have problem with this isolator when my AI Siemens card is active (7kf02)?
 
I would be cautious about what is understood a passive and active. To me the passive isolator is active in that it
"....filters and electrically isolates 0(4) 20 mA analog standard signals, while drawing power for signal transmission from the input
circuit." So it is loop powered from source.

Also, "The connected sensor supplies the passive isolator with the required power, while powering the connected load."

So as I understand it, the connected sensor is 4 wire to power the loop and the Siemens 7KF02 card is configured such that it does not power it's own loop. Unusual and somewhat confusing!
 
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hamid Ankuti

My friend Siemens 7KF02 AI Has 8 channel. on one channel when put in 4-20mA, you have 24Vdc on + & -, because it's has internal supply.
and my transmitter is 2 wire (4-20ma). when you connect + and - of transmitter to + and - of 7KF02 AI, you can read value. but when isolator coming between them, i can't read value. my isolator is Wago 857-451.

i want to know how can i connect this equipment together?

Thanks
 
H

hamid Ankouti

My friend Siemens 7KF02 AI Has 8 channel. on one channel when put in 4-20mA, you have 24Vdc on + & -, because it's has internal supply.
and my transmitter is 2 wire (4-20ma). when you connect + and - of transmitter to + and - of 7KF02 AI, you can read value. but when isolator coming between them, i can't read value. my isolator is Wago 857-451.

i want to know how can i connect this equipment together?

Thanks
 
The spec sheet for the Wago 857-451 says,

"The 1-channel passive isolator filters and electrically isolates 0(4) 20 mA analog standard signals, while drawing power for signal transmission from the input circuit. The connected sensor supplies the passive isolator with the required power, while powering the connected load."
http://tinyurl.com/ntgyszz

In the Teutonic tradition, the documentation shows only connections for the isolator, standing alone, without examples of connections to a source or a load.

So the statement is open to interpretation. I interpret the statement as the source (field transmitter) can be either an active output whose power supply has sufficient capacity to drive both the isolator and the load or a 2 wire loop powered device with a DC power supply for powering the transmitter, the isolator and the load.

Assuming my interpretation is correct, in order to use this passive isolator, you would need to add a stand-alone DC power supply (not the internal DC power in the AI card), in order to power your field transmitter, a 2 wire, loop powered transmitter.

You would also have to change the AI 'Measuring Mode' of the Siemens 7KF02 AI card. It is now configured to supply loop power directly to a field transmitter which conflicts with the isolator's active powered output (by the power suppy on the isolator input).

I'm not a Siemens guy, but a quick read of the 7KF02 manual A5E00253410-04-05/2008
http://tinyurl.com/ogb7tex
shows
4.2.3 Features of the analog modules
Characteristics
- 8 inputs in 4 channel groups (each group with two inputs of same type)
- Measurement resolution adjustable for each channel group
- User defined measuring mode per channel group:
- Voltage
- Current

and in the section following, 4.2.4, is a description of four 'Measuring Range modes' each of which is selected by the position (A, B, C, D) of a rotating device (looks like a square thingie in the photo).

A Thermocouple / resistance measurement
B Voltage (factory setting)
C Current (4-wire transducer)
D Current (2-wire transducer)

You need to set (rotate) this 'Measuring Range' position from the D position (2 wire transducer) to the C position (4 wire transducer) for the pair of AI channels to which you connect the isolator output.

The isolator's active output acts like a four wire transmitter where the newly added DC power supply supplies its power and powers the isolated output. That will match with a C position 4-wire Measure Range mode.
 
H

Hamid Ankouti

Thanks for your reply.

I could understand from your post. i must be use a DC power supply on input of isolator, while i have 2 wire transmitter and put on C position in 7kf02. did i understand correctly?
 
H

Hamid Ankouti

Dear Mr David

>> did i understand correctly?

> Yes.

I test it. on input of isolator i have 4-20mA and my transmitter is on, but i don't have any current in output of isolator and step7. range of AI card is on C also.

Please help me.
Thanks
 
The wiring:
P/S (+) > xmtr (+)
xmtr (-) > Wago #1 IN+
Wago #2 (GND 1) > P/S (-)

Wago #5 > Siemens (+)
Wago #6 > Siemens ground/common

You need to put a current milliamp meter in series in the Wago output and see if the Wago is providing an output. Test your meter first on a known current signal because otherwise a non-reading current is most likely blown meter fuse, believe me.

Disconnect the Wago from the Siemens and test for a Wago stand-alone output current signal. You should get a current reading.

Then re-connect the Wago to the Siemens and check for a Wago current output signal while the Wago is connected to the Siemens.

If the current signal is not coming from the Wago stand-alone, then the Wago is not working.

If the current signal comes from the Wago stand-alone, but doesn't pass through the Siemens, there is a either a connection problem at the Siemens or a Siemens input card issue.

If the Wago current signal goes through the Siemens input card, but your software doesn't read the signal, then it is a configuration issue. I'm not a Siemens guy so I can't help you with that.
 
H

Hamid Ankouti

Dear Mr David

>The wiring:
>P/S (+) > xmtr (+)
>xmtr (-) > Wago #1 IN+
>Wago #2 (GND 1) > P/S (-)
>
>Wago #5 > Siemens (+)
>Wago #6 > Siemens ground/common

I try your connection diagram,but i didn't get answer, and try this connection diagram
P.S (+) > Wago #1 IN+
Wago #2 (GND 1) > xmtr (+)
xmtr (-) > P.S (-)
Wago #5 > Siemens (+)
Wago #6 > Siemens ground/common

Thanks for your reply, you help me until to get answer.

my email is [email protected]
If you come to iran, i will happy to see you and going around the iran.

And thanks for administrator of control website.

Best regards my friend.
 
Thank you for providing the correct wiring solution for a 2 wire loop powered passive field transmitter on the input side of a Wago passive isolator.

It's likely someone will find this in the future and use that information to their benefit.

How gracious of you to extend an invitation to visit. Thank you.

David
 
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