Display and Sensor Issue on 4-20 mA Loop

[LuisGonzalez 0]

Hello everyone,

I'm installing a Vegadis 82 display and a Vegaplus C21 sensor in an industrial application, both connected to a 4-20 mA loop for level measurement. However, I'm encountering an issue:

The Issue: When I connect both the display and the sensor to the 4-20 mA loop, the display doesn't activate. I tested them individually with a 24V external power supply, and they work fine.

Background: We had previously used an Endress+Hauser FMU90, but it frequently provided inaccurate readings and isolated between 0 and a specific value. So, we switched to the Vegadis 82 and Vegaplus C21.

My Questions:

1. Any ideas on why the Vegadis 82 isn't energizing in the 4-20 mA loop?

2. Are there specific configuration settings or adjustments I need to make for this setup?

3. Is it common for display units or sensors to need an external power supply in a 4-20 mA loop?

[pturmel 160]

Are these devices loop-powered?  Are either non-isolated?  Show your circuit diagram.

[LuisGonzalez 0]

Thank you for your response and willingness to assist.

This installation dates back to 2008, and I don't have access to the original wiring diagrams. However, I've created a wiring diagram based on my observations:

 

We're using a GE PLC with the IC200ALG264E Analog Input Module. I'm seeking guidance as I'm not very experienced with this module. Attached are images of the GE module for reference:

 

If there are specific details or questions needed to provide assistance, please let me know. Your insights would be greatly appreciated in resolving the Vegadis 82 and Vegaplus C21 issue in the 4-20 mA loop setup.

Thank you for your support.

[pturmel 160]

You definitely need to power your devices separately.  Per GE manual GFK-1504N, page 10-39:

Quote

The module receives power from the backplane power supply. No external power source is required for module operation. Power for the user’s transceivers must be supplied from an external source.
 

It also extremely unlike that the wiring for the display is correct, as what you show doesn't have the display and input module in series on the signal lines, as is typically required.  Do you have manuals for the display and the transmitter?

(The input module is non-isolated, so it must be the last signal on the current loop.)

[LuisGonzalez 0]

Thank you for your guidance. I'll ensure the ALG266 module is the last device on the 4-20 mA current loop. I appreciate your insights. Additionally, I have attached the manuals for the display and sensor to ensure the correct power supply and wiring. If you have any further advice or considerations, I'd greatly appreciate it.

Thank you again,

47646-EN-VEGADIS-82-4-20-mA-compressed.pdf

58343-EN-Operating-instructions-VEGAPULS-C-21-Modbus-and-Levelmaster-protocol (1)_compressed.pdf

im-45300-en-vegadis-82-4-20-ma-hart-2021-02-15_compressed.pdf

[pturmel 160]

So, the manual for the levelmaster doesn't appear to be the correct one.  It shows Modbus output, not 4-20mA.   Assuming the 4-20mA version is similar, then it is a 4-wire transmitter, not a 2-wire.  You will need to supply power to the transmitter separately from the 4-20mA loop.

Then, you will probably need to wire the display into the signal loop as shown in the Vegadis manual, figure 17 in §5.5.  However, that figure shows an isolated PLC input, and your module is not isolated.  You might want to contact Vega for assistance, as they don't show the non-isolated case.  (Their internal arrangement of sensor and power terminals is not clear.)

[LuisGonzalez 0]

Thank you very much for your assistance,  I'll reach out to Vega's tech support to clarify the non-isolated case. Your insights have been helpful!

Best regards and thank you again,