Communication Issues

No device found 

  1. Verify all connections open circuits, shorts, or bad wiring.
  2. Determine if the loop resistance is at least 250 or higher (max 720)
  3. Check the polling address and duplicate address.

Erratic readings


  1. Verify SME is properly grounded.
  2. Check external electrical interferences

Power issues


  1. Verify correct power levels are applied to the transmitter.
  2. Verify wiring.
  3. Verify voltage drop.

LCD Display 

The SME-TRD device has the capability to blink the HART led to indicate that it is working correctly. HART LED is in the top right corner of the display.




Figure 1. SME-TRD HART led.



Always OFF 

HART disabled 

Always GREEN 

HART enabled, idle state

Blinking GREEN 

Bytes received; command not completed yet

Blinking RED

Bytes received; data corrupted

Always RED

Loop is open, no HART communication possible


What can go wrong with 4 - 20mA loops ?

Connecting 4-20 mA outputs