NORD Drivesystems BU0220 - Manual (Page 40)

PROFIBUS DP – Supplementary manualfor NORD Frequency Inverter SK 2xxE
40 Subject to technical amendments BU 0220 GB-0912
4.2.3 Timeout monitoring
There are two different communication monitoring variants.
4.2.3.1 Access monitoring of DP master
Access monitoring is a monitoring function which is controlled by the PROFIBUS DP master. With this, the DP
master communicates a calculated time interval to each DP slave, within which a communication step must
take place. If this time interval is exceeded the DP slave exits the "data exchange mode" and switches to the
so-called safe mode. The frequency inverter to which it is connected is set to error status (Error E010
→ 10.2).
During system planning, the access monitoring time is automatically calculated for the entire PROFIBUS DP
network by the software tool STEP 7 / SIMATIC Manager. This value usually corresponds to 6x the "worst
case" cycle time, and is in the range between 10ms to 650s.
The access monitoring serves as a protective function against incorrect parameterisation or failure of the
transfer facilities and can by explicitly enabled or disabled for each individual DP slave.
DP slave properties Access monitoring setting
ATTENTION
In case of errors, disabling of access monitoring can result in the outputs of the affected
slaves not being set to "0". It is therefore strongly recommended that the access monitoring
is only disabled for test purposes during commissioning.
4.2.3.2 DP slave watchdog
The technology unit provides an additional timeout monitoring function. This can be enabled by the user in
parameter (P151) "External bus timeout" and set in ms steps. The time-out time must be set to at least 2x
the value of the Profibus cycle time in parameter (P151). This watchdog function is started on receipt of the
first valid PROFIBUS DP telegram (STW Bit 10 = "1" signal ("Process data valid")).
If all process data telegrams (PZD) are declared as invalid (STW Bit 10 = "0") the error message E10.2 is
generated. The bus module switches off all of its outputs (0V). This situation occurs if the automation device is
in STOP mode and the PROFIBUS DP master continues to send telegrams with data content "0".
As long as one of the connected frequency inverters is still in an error status, i.e. an error message has not
been acknowledged, the technology unit remains in timeout error status.