Allen-Bradley 1444-TSCX02-02RB User Manual page 488

Appendix A CIP Objects
Table 235 - Tacho (eTACHO)
Byte Offset Structure Member
Within Structure
0 TimestampNanoSec
4 TimestampSec
8 Reserved
12 Reserved
16 Reserved
20 ByteCount
34 TimingArray
488
Reference the measurement tables.
Data Type Description
UDINT Subsecond accuracy.
UDINT Seconds since 1970.
REAL
DWORD
UDINT
UDINT The size of the following array in bytes.
UDINT The array of tacho time values (24 bit, micro-second counter).
For FFT and TWF data
For asynchronous data, the actual sample period is transferred (REAL format).
For synchronous data, the same four bytes are used to transfer the number of
samples per revolution and an indicative speed for the transferred data.
Number of samples per revolution occupies the first byte, the remaining 3 bytes
are used for a scaled speed value (speed x 100). This format supports speed
values to 167,772.15 rpm with a resolution of two decimal places.
Example with 'data on the wire' of 0x 10DC7D05:
• 0x 10 = 16 samples per revolution
• 0x 057DDC = 359,900
• RPM = 359,900/100 = 3599 rpm (60 Hz)
Whether the data is asynchronous or synchronous can be known from the
identifier field. This has the following format.
Bits Description
0...1 Measurement channel (0, 1, 2, 3) from which the data originates
2 Data source (Transfer path 0 or 1)
3...4 Transfer path 0 data source (0 pre-filter, 1 mid-filter, 2 post-filter)
5...6 Transfer path 1 data mode (bit 5 = 0 asynchronous, bit 5 = 1 synchronous, then bit 6 indicates
which tacho was used)
7 Associated tacho source from the Normal CM Data Object
8...15 Measurement engineering units (index not CIP code)
16...31 The 16-bit tacho event counter (cross module synchronization scheme)
Rockwell Automation Publication 1444-UM001D-EN-P - June 2018