Analog Woes

Hi Guys!
I'm having real difficuly connecting a Lem current transducer (AT 100 B420) to a ET200s Analog module (6ES7 134-4GD00-0AB0).

I've tested the analog module with a 4-20ma generator all ok. And I've wired my meter in series with Lem when not connected to the analog mdule and get 4ma. But when I connect the two together I get nothing?
I've tried wiring the Lem directly to the analog module and in a powered loop but get nothing either way (

Am I missing something, it's been a while since I've messed around with this stuff.

Thanks

Roger

Do you have the polarity right?

Do you need to have a voltage source in the loop to power it?

The DK 100 B240 is a 4 wire device, requiring a 24Vdc power supply.

Presumably, if you checked its output and got 4mA, then there's a power supply connected to the CT.

When you checked the output of the CT with a meter in series with the output, was the meter battery powered (hence, floating)?

If the power supply is grounded and your analog input is 'single ended' then the AI's (-) is grounded, and a ground loop can develop between the AI ground and the power supply ground. A ground loop can drive the signal off scale.

Is the power supply floating?

Thanks for the replies.
Not sure where the DK come from? The AT 100 B420 is a 2wire device

https://www.dropbox.com/s/jh15i6jv7oo7mal/AT 100 B420.pdf


Data sheet for et200s module
https://www.dropbox.com/s/koo1tlj03qfdc67/et200s_4ai_i_2wire_st_manual_en-US (1).pdf


I'm using a 24VDC power supply that doesn't have the 0V grounded to earth so I guess that's floating?

Thanks for the help guys

The way I interpret the ET200S block diagram is that this analog input module is designed to power 2 wire, loop powered devices with its own module's loop power.



The block diagram shows DC power, P1 or L+ (over on the left side) connected to terminals 1/3/5/7 which would wire to the CT's positive terminal, providing DC power to the CT. The CT's negative terminal wires back to ET200S terminals 2/4/6/8. The load resistor for the analog input is internal to the module with connections from each side of the load resistor running to the ADU.

The AT 100 B420 manual shows the typical wiring circuit for a 2 wire loop powered device, with an external power supply. But since the ET200S provides DC power, you should use an external power supply with this analog input module

danw said:

The AT 100 B420 manual shows the typical wiring circuit for a 2 wire loop powered device, with an external power supply. But since the ET200S provides DC power, you should use an external power supply with this analog input module

Click to expand...

I had tried using the ET200s dc power and an external power supply but got no joy. Do you think the issue is down to using a floating supply as you suggested in your first post?
I'm at home now but will try grounding the supply when I get back to work on Monday.

Thanks again

Roger

Sorry, I can't proof my own writing.

My last statement should have been, "But since the ET200S provides DC power, you should NOT use an external power supply with this analog input module.

Since the module sources DC power, you do not want to use an external power supply.

Just connect the CT's (+) to an odd numbered ET200S terminal, and connect the CT's (-) to an adjacent even numbered terminal.

danw said:

Just connect the CT's (+) to an odd numbered ET200S terminal, and connect the CT's (-) to an adjacent even numbered terminal.

Click to expand...

Tried doing that and it goes into overflow range.
I've also now linked my 0V to earth and still get the same issue.

Thanks

Roger

Do any of the inputs on this card function properly? I suspect that an external 24Vdc in the loop might have fried the card.

Does the card still 'see' your 4-20mA simulator in 2 wire mode?

Take the ground off. Grounds can be an issue with AI's.

You might have to use an isolation transmitter.

danw said:

Do any of the inputs on this card function properly? I suspect that an external 24Vdc in the loop might have fried the card.

Does the card still 'see' your 4-20mA simulator in 2 wire mode?

Take the ground off. Grounds can be an issue with AI's.

Click to expand...

Sorted! Whilst re-checking the inputs with the simulator I noticed something. When I put 4.000mA on the input i get an overflow value, however when I put 4.001mA it works!
According to the manual I should have had a different value for underflow? I don't care anymore spent enough time on this.

Thanks for all the help!

I'm glad the power supply didn't fry the board.