HEIDENHAIN PWM 20 - Manual (Page 233)

234 HEIDENHAIN ATS Software User's Manual
Monitoring and
diagnostic
functions The EnDat interface enables comprehensive monitoring of the encoder without requiring an
additional transmission line. The alarms and warnings supported by the respective encoder are
saved in the "parameters of the encoder manufacturer" memory area.
Error message
An error message becomes active if a malfunction of the encoder might result in incorrect
position values. The exact cause of the disturbance is saved in the encoder’s “operating status”
memory. It is also possible to interrogate over the additional information “operating status error
sources.” For this purpose the EnDat interface transmits the error 1 and error 2 error bits (only
with EnDat 2.2 commands). These are group signals for all monitored functions and serve for
failure monitoring. The two error messages are generated independently from each other.
Warning
This collective bit is transmitted in the status data of the additional information. It indicates that
certain tolerance limits of the encoder have been reached or exceeded—such as shaft speed
or the limit of light source intensity compensation through voltage regulation—without implying
that the measured position values are incorrect. This function makes it possible to issue
preventive warnings in order to minimize idle time.
Online diagnostics
Encoders with purely serial interfaces do not provide incremental signals for evaluation of
encoder function. EnDat 2.2 encoders can therefore cyclically transmit so-called valuation
numbers from the encoder. The valuation numbers provide the current state of the encoder and
ascertain the encoder’s “functional reserves.” The identical scale for all HEIDENHAIN encoders
allows uniform valuation. This makes it easier to plan machine use and servicing.
Cyclic redundancy check
To ensure reliability of data transfer, a cyclic redundancy check (CRC) is performed through
the logical processing of the individual bit values of a data word. This 5-bit long CRC concludes
every transmission. The CRC is decoded in the receiver electronics and compared with the data
word. This largely eliminates errors caused by disturbances during data transfer.