10
LH 5946 / 130910 / 363
The LH 5946 can be used for standstill detection on all 3-phase, single
phase and DC motors, that generate a voltage caused by remanence when
freewheeling. As the voltage level Uan for standstill monitoring and the time
delay ts, after detection of standstill until the safety relays are switched on,
are adjustable, the function can be adopted to different
motors and applications.
Basic function of LH 5946
The auxiliary voltage is connected to the terminals A1-A2; the LED „UH“
lights up green. On undervoltage or missing auxiliary supply the safety
outputs are disabled.
If semiconductor monitoring outputs are used, their supply voltage must
be connected to A3(+)-A4.
A motor connected to the terminals L1-L2-L3 of the LH 5946 generates
a voltage when running down (motor is switched off). The voltage is pro-
portional to the speed and caused by residual magnetism (remanence).
This voltage is measured redundant on 2 input channels via the terminals
L2 and L3 with L1 as common reference.
If the voltage drops on both channels below the adjusted value U
an
, the
unit detects standstill. When the terminals X1-X2 of the feedback circuit are
bridged and the time delay ts is finished, the safety contacts 23-24, 33-34
and 43-44 close while contact 11-12 opens. All 4 contact paths have 2
forcibly guided contacts of 2 safety relays wired in series.
At the same time the monitoring relay energises (53-54 closes), the se-
miconductor output „ON“ is switched on and the LED „OUT“ lights green.
During time delay ts this LED flashes.
If the voltage measured on terminals L1-L2-L3 of LH 5946 rises over the
adjusted value plus hysteresis in at least one channel (the motor is switched
on or the shaft turns mechanically), the forcibly guided output contacts are
switched off immediately (contacts 23-24, 33-34 and 43-44 open while
contact 11-12 closes). The monitoring relay de-energises (53-54 opened),
the semiconductor output „ON“ goes off and the LED „OUT“ lights yellow
(= U
an
over adjusted value).
Feedback circuit X1 - X2
If the safety contacts control external contactors/components (e.g. to re-
enforce or multiply the contacts) the safety function of them must be monitored.
This is done with the feed back circuit (terminals X1-X2) to which the NC
contacts of the contactors/components must be connected. (see also
wiring diagrams).
The LH 5946 will only enable its safety output if the feedback loop X1-X2 is
closed while standstill is detected, i.e. the external contactors/components
are in initial state (NC contacts are closed).
The feedback circuit X1-X2 must be closed as long as the safety outputs
(because of running motor or external failure) are not enabled. If not the
failure „feedback circuit“ is indicated.
If the feedback circuit is not used, the terminals X1-X2 must be bridged.
Function
Failure monitoring
The LH 5946 includes a number of facilities to to detect failures that could
influence the safety function of the module. The failure check is carried out
on power up of the unit and in cycles during normal operation. If a failure
occurs the output relays switch off. The failure state is indicated with the
LEDs „ERR“ and „UH“ and the semiconductor output „ERR“ switches on.
With safety relevant failures the unit differentiates between external failu-
res (broken wire / offset, simultaneity failure, feedback circuit failure) and
internal failures.
Broken wire / offset failures and feedback circuit failures can be stored
or automatic reset after removing the fault. (see chapter failure storing).
Broken wire / offset
The connection wires between LH 5946 and motor are continuously
monitored for broken wire and on a DC-voltage offset higher then U
an
.
In the case of a broken wire or offset failure the output relays
are switched off immediately and the LED „OUT“ lights yellow.
In addition a failure signal comes up with delay (on broken wire after 2 s on
offset failure after 8 s): the semiconductor output „ERR“ switches on and
the LED „ERR“ flashes with failure code 2 or 3 depending on the failure
located either between L1-L2 or L1-L3.
Simultaneity of the measuring signals
As additional safety feature the 2 input signals (L2 and L3) are compared
continuously. This allows to detect also internal failures in one measuring
channel.
If the signals are different for at least 2.5 s (one channel >U
an
the other
<U
an
) simultaneity failure is detected. The semiconductor output „ERR“ is
switched on and the LED „ERR“ flashes with failure code 5.
If the measured signals return to the same level <U
an
the error remains
stored and the outputs are disabled.
The simultaneity failure is only reset when both channels return to > U
an
.
If after that both channels drop below the setting value, get < U
an
the out
relays will switch on.
Failure in feedback circuit X1-X2
As already mentioned the failure code „feedback circuit“ occurs when the
outputs are disabled and there is no connection between terminal X1-X2.
The semiconductor output „ERR“ is switched on and the LED „ERR“ flashes
with failure code 4.
Also when both input signals drop now to <U
an
and besides the open feed-
back loop no other failures are present the feedback circuit failure remains
active and the outputs remain disabled.
If the feedback circuit is now closed and the unit is on auto reset for external
failures (see failure storing) the output relays are enable and switch on.
Internal device failure
Internal failures are always stored, independent of the reset input X3 and
cause the output relays immediately to switch off, the semiconductor output
„ERR“ to switch on and the LED „UH“ to change it’s colour from green to red.
Examples for internal failures:
•
Failure on safety relays e.g. welded output contacts
•
Internal failures on measuring channels and measuring circuits
•
Internal failures on control circuits for the safety relays
•
failures on setting potentiometers for U
an
and t
s
•
Undervoltage failure (LED „ERR“ flashes with failure code 1)
Function
