A threshold value to check against if mteTriggerType is
'threshold'.
When the current sampled value is greater than or equal to
this threshold, and the value at the last sampling interval
was less than this threshold, one
mteTriggerThresholdRisingEvent is triggered. That event is
also triggered if the first sample after this entry becomes
active is greater than or equal to this threshold and
mteTriggerThresholdStartup is equal to 'rising' or
'risingOrFalling'.
After a rising event is generated, another such event is not
triggered until the sampled value falls below this threshold
and reaches mteTriggerThresholdFalling.