Hi! Please help me to establish the HART communication with Berthold radioactive multi detector HART output loop. The HART communication with single detector is working fine. where as the HART loop having two sources and two detectors with one HART current loop is not communicating with 375 field communicator, even with "always poll" option. Supply voltage & loop resistance are good.

 

From HART's application guide, page 8:
http://www.hartcomm.org/hcf/documents/appguide.pdf
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The multidrop mode of operation requires only a single pair of wires and, if applicable, safety barriers and an auxiliary power supply for up to 15 field devices (Figure 3).

All process values are transmitted digitally. In multidrop mode, all field device polling addresses are >0, and the current through each device is fixed to a minimum value (typically 4 mA).
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Most HART devics default to address 0, for the traditional point-to-point operational mode, where you have only a single HART device on the link.

Make sure you change the address value of each xmtr to something greater than 0, (like one or two) but give each device a different address.

David

 

Hi David

Thanks for reply.

in our application, we have two radioactive sources & detectors (one main unit & another one axillary unit) for a level measurement and the HART output is wired to control system from main unit. when HART communicator is connected this loop, it is not identifying the device, even with "always poll" option which Connects to a device at address 0 and if not found, the communicator will automatically poll for devices at addresses 1–15. so in our case, even if the main unit is having poll address other than"0" also, HART should identify. but it failed. whereas the HART communication with level measurement having single detector is working good. please note this is not in field bus.

Thanks

Regards
Thangs

 

1) Are both detectors are on the same 4-20mA link back to the control system?

It isn't clear what you mean by "wired to control system".

Is each detector wired to its own control system analog input?

Or are both wired to a HART multiplexor?

2) What is the HART address of each device: main device, aux device ?

 

In multi detector level measurement, the axillary unit is wired to Main unit through RS485 and the main unit HART output is connected to DCS for indication. that means only one output from this level detector and so they are not connected to any HART multiplexer. since we could not establish the HART communication, we could not identify the address of these devices.

 

What model level device are you using? LB490?

 

Is there a minimum of 230 ohm resistance in the 4-20 mA loop? If not HART will not work - if not, include a resistor. Also make sure there is not a lot of AC noise.

Cheers,
Jonas