AM2Q, Voltage on current output?

Hi all,

I am wondering about the following. 

An  AM2Q is connected to a logo BA8.

I have set AQ1 and AQ2 to be a 4-20ma output 

If i measure the voltage between Mx and Ix terminal i measure 13.49V  !!!!

Is this not strange. 

What if we  want to connect the 4-20ma logo Output to an measuring device that accepts a 4-20ma input and on this input we also measure a voltage. Will this not lead to problems.

I can understand that the measuring device has a voltage on his 4-20ma input, because there will be a passive 4-20ma sensor connected to the device input. The voltage  will power the 4-20ma sensor.

Should there be a voltage on the Logo 4-20ma analog output, or do i see this completely wrong.

Thanks in advance for your time.

Fabrizia

No thats normal.

You want to meassure a currend and you set your meter on voltage!

Think about the difference if you want to measure a voltage (zb an elektric plug = 230V) and you set your meter on Amperes and then....

If you use a CURREND output, then you can measure only a correct Currend if the resistance in the output is not to high (think about 500 - 1000 Ohm)

You must think in Current (mAmperes) not in Voltage. If the LOGO wants to make 15 mA on the output what is than the voltage?

Law of Ohm, U = I x R, You know the I, what is R?

Thank you for answering.

Indeed when placing a current meter in serie with an 220 ohm resistor between M1 an I1 i measure spot on 4-20ma.

And at 20ma i have a voltage drop of 4.4V over M1/I1.

There has to be a potential difference to have a current flowing.

Attached is a hopefully better description of what i intended to ask in this topic.

Best regards,

Fabrizio

If the smartbox has a normal signal input 0/4-20mA, this will have a low resistor e.g. 500 Ohm from input + to input -. There is no cross or cylce voltage or current. The higher voltage only occur with a higher resistor as you have at the input of a voltmeter, e.g.10 MOhm.

Regards, Scorp

P.S. Upload a link to your smartbox, if you want to checked from us, that the input can be used as you want.

Notice: LOGO AM2 module has an AKTIVE 4-20mA output.

Have you more information of your smartbox?

Hi,

Here is a link to the user manual of smartbox device.

https://www.manualslib.de/manual/464906/Gok-Smartbox-4.html?page=6#manual

It is in German, i could not find the Englisch version.

On Page 6, they specify the Input connection to the sensor.

They only say that smartbox provides 20V DC to power the 4-20ms sensor.

I have send a mail to smartbox to ask them about the connection to an active 4-20ms sensor.

Best regards,

Fabrizio

In this case it may not be good to connect to the Logo AM2 AQ. The sensors are 2-wired, then + may be DC20V and - is the 0/4-20mA input, internally connected to ground. But there are no terminals for ground. Ask the customer of the smartbox in details for connection with a current output, not a 2-wire-sensor.

Regards, Scorp

I received reply form smartbox.

"

the 4-20 mA input of SmartBox is only for passive 4-20mA signals (as you know) and it’s not possible to change this at the SmartBox.

It will not work with an active 4-20 mA signal, because of two supply voltages.

Is there a way to configure the Logo module to get a passive signal?

"

Is it possible to change a setting in logo to get an passive 4-20ma output?

My idee was to use logo to duplicate the 4-20ma current from  a passive sensor. 

Best regards,

Fabrizio

There is nothing to change at the Logo AM2 AQ, the connection is then not possible. Maybe you get another solution to duplicate the sensor values. Check the smartbox for a LAN connector with ability of Modbus TCP/IP. If available, then you can transfer the value over LAN connector of the Logo. The Logo is able to be Modbus TCP/IP client or server.

Regards, Scorp