Fault Signalling

The SITRANS LC 500 has three fault signalling options:

via the loop-current

via HART

via the solid-state output or solid-state relay.

Via the loop current

When using the mA signal, the SITRANS LC 500 operates according to NAMUR standards1 for fault signalling. The fault/failure signal can be triggered by a failure in the measuring system, such as:

a checksum error

a loss of signal caused by a defect in the module

a short circuit in the sensor

a process failure if the level exceeds the limit settings and if the unit is programmed to detect this

You can set the Upper and Lower Sensor Limits (menus 0B and 0C) outside the Upper and Lower Range Value settings. In this case, if the process value is outside its nominal range (the span between LRV and URV), but still not at a fault/failure level, the continuous mA output will saturate to 3.8 mA or 20.5 mA. If the process value is outside the Upper or Lower Sensor Limits, this will be registered as a fault/failure.

Depending on the setting chosen for 2-state Fault Signalling (menu 08), the signal will go to either 3.6 mA (F: Lo) or to 22 mA (F:Hi). If you do not use communications to receive status information, we recommend enabling analog fault signalling (menu 08), in order to be warned if a fault or failure occurs. (This feature is disabled by default.)

Via HART

See page 75 for HART Response Code Information. Each HART message is accompanied by a response code. It is then up to the Host to decide what to do in the case of a fault situation. The Host may decide to issue Command 48, which returns more detailed information.

Via the solid-state output

The solid-state switch can be wired up to an external relay, to provide a second level of protection. It can then be used to activate a failure alarm, or a level switch. (See page 93 for details of an application using SITRANS LC 500 as a level indicator, with the two-state output connected to a relay that activates a pump.)

1.See NAMUR recommendation NE 43 on page 107 for more details.

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SITRANS LC 500 – INSTRUCTION MANUAL

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Operation & Application

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Image 21
Siemens Sitrans, LC 500 instruction manual Fault Signalling, Via the loop current, Via Hart, Via the solid-state output