Mitsubishi MELSEC-WS series, User Manual

Page: 41 / 152

Chapter 3
38
Product description
3.8.5 Extended fault detection time for cross-circuits on the outputs Q1 to
Q4 on the WS0-XTIO for switching loads with high capacitance
From firmware version V3.10 it is possible to configure an extended fault detection
time for cross-circuits for the outputs Q1 to Q4 on WS0-XTIO modules.
This configuration can be necessary for switching loads on which there is a cross-
circuit fault immediately after switching off (change from high to low) with a normal
fault detection time because the voltage at the load does not drop to the low level as
quickly as expected. Examples of such cases are:
 Loads with higher capacitance than permitted as standard for the output, e.g. the
supply voltage for programmable controller output cards for safety-related
switching.
For this application the test pulse for the output must also be deactivated (see
section 3.8.4).
 Inductive loads that cause an overshoot in the positive voltage range after the
induction voltage has decayed.
WS0-XTIO
firmware
Version
Option for switching loads
with high capacitance
Maximum time to low level ( ≤ 3.5 V)
allowed after switching off the output
(Q1 to Q4)
≤ V2.xx Not possible 3 ms
≥ V3.10 Deactivated 3 ms
Activated 43 ms
The capacitance beyond the value that is permitted for the output as standard must be
discharged to the low level in the customer’s installation after switching off the output.
If this condition is not met within the maximum time allowed, there will be a cross-
circuit fault on the output independent of whether the test pulses on this output are
activated or deactivated.
Pay attention to the suitability of the programmable controller output card for
the safety-related shut down of the outputs by switching the supply voltage!
The safety-related shut down capability can be affected or even lost as a result of the
following faults:
 Undetected cross-circuit on an output on the programmable controller output card
that can result in the reverse supply of the programmable controller output card.
In some circumstances this fault can be excluded by laying wiring in an
adequately protected area.

Undetected fault on the programmable controller output card that can result in the
external supply of the programmable controller output card by another live signal.

Extension of the response time by a buffer capacitor in the supply for the
programmable controller output card.
Please note that the outputs on the WS0-XTIO modules cannot discharge this
buffer capacitor, as it is normally behind a reverse polarization protection diode.
Table 15:
Maximum extended fault
detection times for cross-
circuits on WS0-XTIO
ATTENTION