4-20mA Inputs to E4 UC 12RC1 operating on 24VAC

[Simon Tyrcha]

Is it possible to use 4-20mA inputs on an easy E4 UC 12RC1 which is supplied by 24VAC? Thank you!

[Konni66]

Hello Simon,

this should work if You use a 500 Ohms resistor to convert 4..20 mA into 2..10 V.

500 Ohms resistors are available exactly for this usage.
Or use a 499 Ohms resistor from E96 series.

Have a look at the attached picture.
Notice: You must connect 24 VDC-sensor-GND to easy's 24-VAC power-supply's 0 V.

Greetings
Konni

[Simon Tyrcha]

Vielen Danke!!!

Thank you!!!

[Simon Tyrcha]

Hello Simon,

this should work if You use a 500 Ohms resistor to convert 4..20 mA into 2..10 V.

500 Ohms resistors are available exactly for this usage.
Or use a 499 Ohms resistor from E96 series.

Have a look at the attached picture.
Notice: You must connect 24 VDC-sensor-GND to easy's 24-VAC power-supply's 0 V.

Greetings
Konni

Vielen Danke!!!

[Simon Tyrcha]

Hello Simon,

this should work if You use a 500 Ohms resistor to convert 4..20 mA into 2..10 V.

500 Ohms resistors are available exactly for this usage.
Or use a 499 Ohms resistor from E96 series.

Have a look at the attached picture.
Notice: You must connect 24 VDC-sensor-GND to easy's 24-VAC power-supply's 0 V.

Greetings
Konni

Please excuse my email inquiry regarding how to attach images. I have found the function to do so.

Can you please tell me if my diagram in the attached image is correct based upon your advice?

Thank you!!!

[Konni66]

Hello Simon,

I think, it will not work. What about the DC-GND? It's connected to (space)

Please show the sensor's data sheet to us.

Greeetings Konni

[ELWMS]

Hallo Simon!

I think it won't work. The analog input has the same internal reference point as the supply voltage. However, the UC device is operated with AC. the reference point is therefore not stable. The analog input works with 0-10VDC. It is not clear from the technical data whether mixed operation is possible. An EASY-E4-DC-6AE1 will probably have to be used because the electrical isolation is there.
12DC GND has to be connected somewhere. This is the reference point for the 12VDC.

But if an EASY-E4-DC-6AE1 is used, the supply voltage for the extension must be 24VDC, or would 12VDC also work?

Gruß,

ELWMS

SRy, mein Englisch ist etwas eingerostet...

[Konni66]

Hello,

EASY-E4-DC-6AE1 does not work at 12 VDC - data sheet shows 24 VDC only.
The DC-GND must be connected to AC-0V.
Otherwise the DC (current from sensor over 500 Ohms) input voltage has no reference point.

[Simon Tyrcha]

Hello Simon,

I think, it will not work. What about the DC-GND? It's connected to (space)

Please show the sensor's data sheet to us.

Greeetings Konni

 :)Of course you are correct!!!

I am new to working with analog devices, as you can likely tell, and misunderstood your diagram. I see now where the resistor in your diagram is going to ground.

I will attach photos of the power converter I am using, and a copy of the sensors data sheet, as well as an updated version of my diagram for your consideration.

Thank you very much for your support.

[Simon Tyrcha]

Hallo Simon!

I think it won't work. The analog input has the same internal reference point as the supply voltage. However, the UC device is operated with AC. the reference point is therefore not stable. The analog input works with 0-10VDC. It is not clear from the technical data whether mixed operation is possible. An EASY-E4-DC-6AE1 will probably have to be used because the electrical isolation is there.
12DC GND has to be connected somewhere. This is the reference point for the 12VDC.

But if an EASY-E4-DC-6AE1 is used, the supply voltage for the extension must be 24VDC, or would 12VDC also work?

Gruß,

ELWMS

SRy, mein Englisch ist etwas eingerostet...

Vielen Danke! Mein Deutsch ist auch sehr rostig!!! Aber besser als mein verstandnis von analog circuits!!!

[Konni66]

Hello Simon,
your diagram looks good to me. That's the way I would try.

PS:
Remember, the resistor should be placed near easyE4 - not located at the sensor.
We want to use the advantages of a current interface and transform it to voltage near the analogue input. Otherwise you'll get unstable measuring values.

Greetings Konni

[Simon Tyrcha]

Hello Simon,
your diagram looks good to me. That's the way I would try.

Greetings Konni

Vielen Danke, Konni!!! Ein schones wochenende!!!

[Simon Tyrcha]

Hello @Konni66

I am just returning to this project after my still successful battle with cancer, and I am having some issues.

The diagram that I am working from does retrun an analog value, however, its scale is off, and it causes a very high power consumption which has burnt out several fuses and a 500mA power supply.

I have tested the analog device, and it is calibrated correctly, and functions properly when used as a 4-20mA device in conjunction with my process meter; only drawing between 4 and 20 mA.

The manufactutrer of the level sensor advised using an additional resistor, however, this has not returned any stable values, and still draws over 500mAs.

In the attached picture, the first is wired as per the diagram you thought would work, and the second is with the additional resistors suggested by the level sensor manufacturer.

Please advise.

Danke!

[radar17892]

Hi Simon,

I can't see why the short circuit occurs. It needs a voltage of 250V to drive a current of 500mA through the 500Ohm resistor to ground. And the current to the Input's I5-I8 is ~1,8mA.
Where in the diagramm is the fuse? If the fuse was burnt out, is the Resistor OK??
Greedings Thomas

[Simon Tyrcha]

Thank you, Thomas!

In all honesty, I made a huge mistake by not including a fuse in the initial mock-up of this test, and it cost me a 500mA 24VAC power supply. The controller still seems to work. I have since included a fuse; first placed ahead of the main input to all attached devices (controller, 24VAC - 12VDC power converter, and sensor), and after that 500mA fuse failed, moved the fuse to just the sensor, which cost a second 24VAC power supply. Following that, I attempted several differing configurations with the 500mA fuse just after the 24VAC power supply, and each attempt cost an additional 500mA fuse.

Currently, I have wired the controller to operate on the same 12vdc circuit that the sensor operates from, and have a 250mA fuse after the 12vdc power converter and ahead of the controller and sensor, and I have a successful result. While I could use this approach in our project, I would prefer to retain the use of the 24VAC input to the controller, and would like to determine why the short circuit is occouring.

The resistors are all still measuring between 480 and 500 ohms.

To recap:
The original wiring was:
Main inlet power supply of 24VAC feeds the controller and the 24VAC-12VDC power converter in parallel.
The 12VDC power converter - output is connected back to the controllers 0 volts input and has a 500 ohm 1 watt resistor between the controllers 0 volts input and I5.
The sensors + volts lead is connected to the 12VDC power converter + volts output, and the sensors - volts lead is connected at the controllers I5.

I believe this should work; however, it is not.

I appreciate any help from the forum!

Thank you!
Simon