How to Connect a two-wire level probe to a four-wire configured Siemens Plc card???

Hi Guys!

Could some one please help out here!

I had to change a failing four-wire silo level probe at work.
I found that the spare at my disposal is a two-wire vega probe.

The analog card is configured for four-wire inputs.

I would like to use the same card's slot for my two-wired probe.

Please advise , how should I go about this one without having to change the card's cofiguration, as this will,presumably, affect other instruments( four-wire) already connected to the card.

I would be grateful for assistance.

Regards

Man G

To be able to help you, you need to help us, with a model of PLC, the type and model of PLC card, the type and model of your level probe, is it 0-10volt or 4-20 mA.

Supply the instrument with 24VDC from another source than the card, bring the + from the instrument to the PLC Card +, then from the PLC card - to the common of the 24VDC power source. What the PLC card sees is the same as if the instrument were a 4 wire device.

jtn said:

Supply the instrument with 24VDC from another source than the card, bring the + from the instrument to the PLC Card +, then from the PLC card - to the common of the 24VDC power source. What the PLC card sees is the same as if the instrument were a 4 wire device.

Click to expand...

Oops, wrote that in too big a hurry last evening. What I should have written: Supply the instrument with 24VDC from another source than the card to the instruments +, bring the - from the instrument to the PLC Card +, then from the PLC card - to the common of the 24VDC power source. What the PLC card sees is the same as if the instrument were a 4 wire device.

Jtn is right, if you don´t know what type of CPU or Analog input card. If it is an S7-300 analog input card, just change the switch from "C" to "D", and wire the + of the sensor to the + of the input, and the - of the sensor to the - of the input. just remember that the switch is for 2 inputs.

Eurika!!Thanks jtn. I now have a working silo level probe. I trully appreciate such an intelligent contribution.

As for nonuke and Gil47, the Plc is a 300s7 , 24V, 4-20mA anlog card. The level probe is a Vega ultrasonic one. But that's beside the point now as the level input is reaching the plc and shows on the scada. And this is as jtn suggested.

Thanks all of you guys for your help

Regards

Man G