Siemens S7-300 Installation And Operating Manual page 156

Digital modules
8.6 SM 326; DO 10 x DC 24V/2A (6ES7326-2BF01-0AB0)
Incorrect diagnostics of a wire break at the redundant digital output modules
Redundant operation of fail-safe output modules SM 326; DO 10 x DC 24V/2A can result in
the following behavior in case of an error: In addition to reporting a wire break and the
corresponding faulty channel, the module also reports faults at one or several other channels
if operating withdifferent load circuits.
Figure 8-49
Example
The module in this example reports faults at channels Q0 and Q1 after having detected a
wire break at Q0. This is caused by severe load differences between the two channels: 2 A
and 24 mA.
Remedy
The load at the output channels of the module should be close to equal in order to obtain
correct diagnostics data. That is, a low-to-high load ratio of at least 1:5 should be
maintained.
156
Incorrect diagnostics of a wire break at the redundant SM 326; DO 10 x DC 24V/2A
Installation and Operating Manual, 01/2010, A5E00085586-10
Fail-safe signal modules