ABB SA/S 12.16.6.1 Product Manual - Knx Device
ABB i-bus
®
KNX Device
technology
SA/S | 2CDC 505 056 D0207 39
It is possible to program two threshold values for each output. With an
overshoot or undershoot of the current threshold value a 1 bit telegram is
sent on the bus. Thus for example, the failure of equipment can be detected
and displayed.
With relatively small current values (< 30 mA), natural deviations in the
electrical system will be immediately noticeable, e.g. natural ageing of the
equipment, voltage fluctuations through differing load levels during the day
as well as distortions of the sinusoidal load current, e.g. through switching
actions or frequency inverters.
The ideal observation, where the current consumption of the equipment
does not change with temperature fluctuations, operating voltage deviations
and ageing should be inspected in real systems. The changes of the
ambient conditions in practice and the associated changes in current
consumption and the monitored equipment must be considered. As ambient
influences cannot be eliminated in practice, the detection via a current
threshold model is only viable if a current change caused by tolerances and
ambient influences in normal operation is less than the current change
caused by failure of the equipment.
Recommended approach when monitoring loads that are close to the
detection tolerances of the SA/S current detection:
Connect the complete current circuit on the SA/S output.
Connect the current circuit and operate the loads in the typical operating
range.
In the ETS, set the data point types of the communication object and
start the ETS project group monitor in order to display the current value.
Observe current value I
A
via KNX until a constant current is indicated.
Cause equipment failure and observe the current value I
F
again.
Determine the difference in current I
D
= I
A
– I
F
.
Compare the difference in current I
D
with the current detection
tolerances. The current difference must be significantly larger than the
accuracy of the current detection (2 % of I
A
+/- 20 mA).
Set the current threshold in SA/S so that it is as near as possible to the
determined failure current: I
A
– ½ I
D
has proven useful.