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Standard acquire-on-change will grab incoming data based on on absolute change. This is not desirable when taking insulation resistance readings, as an absolute change of 10 k Ohm from 1 M Ohm to 990 k Ohm will happen very frequently, due to wet weather for instance, and not warrant any corrective actions, where . Whereas a change from 55 k Ohm to 45 k Ohm would cross an alert boundary and warrant immediate corrective action.

Setting a small acquisition threshold will cause a large amount of not very useful data to be captured, whereas setting a large threshold would cause low data volumes, but reduce sensitivity to genuine fault conditions.

To counter this, the "relative" acquire on change method must be set on the logger. To do this requires the use of the "Rail Event" feature of the SA380TX.

1) Open the "Rail Events" Tab - This is where we can create all sorts of clever acquisition rules.

RAIL EVENT TAB

2) Create a new "Rail Event" - This sets up a new set of acquisition rules. It is OK for your Rail Event to errors at this stage.

CREATE NEW RAIL EVENT

3) Create the "Start Trigger" - We want to acquire data when the SA380TX boots up, and then whenever there is a significant change in insulation resistance. Whenever there is a +/-5% change in insulation resistance, a new acquisition is started. It is OK for your Rail Event to errors at this stage.

SET START TRIGGER

4) Tell the SA380TX what to Acquire - We want to keep acquiring insulation resistance values so long as they continue change. Every time the insulation resistance changes by another 5% of its prior value, we grab another sample. It is OK for your Rail Event to errors at this stage.

SET ACQUISITION

5) Set the end conditions - We don't need an "end trigger" we keep on acquiring samples so long as they continue to change. At some point though we want to barrel these samples up and send them to Centrix. This is why we put a time-out period of 1 minute in place.

After 1 minute acquisition will end, and all samples acquired since the start trigger event will be sent to Centrix. Don't worry though, next time Insulation resistance changes by 5%, a brand-new acquisition will be triggered and the whole process repeats.

Your Rail Event should now have no errors.

END TRIGGER

SET END TRIGGER

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