MoTeC ACL VIM - Manual (Page 22)

18 Operation
Update Rate
Each input is measured at a maximum rate which is dependent on the
capabilities of the measuring device and may also vary between inputs on that
device. For example the VIM has some inputs that update at 500 Hz and
others that update as fast as 5000 Hz.
Refer to Appendix E: Update Rate Summary.
Anti-Alias Filter
If a channel is logged at a rate slower than its specified update rate then an
optional anti-alias filter can be applied.
The anti-alias filter is used to average out any variations in the signal between
logged values. This ensures that unrepresentative values are not logged.
The anti-alias filter is implemented by averaging the channel values between
logging events. For example, if a channel has an update rate of 1000 Hz and
it is logged at 100 Hz then the preceding 10 samples will be averaged each
time it is logged.
The anti-alias filter is normally turned on by default when a channel is added
to the logging list, but may be turned off if required. For normal purposes it is
recommended that the anti-alias filter is left turned on.
Note For some channels the anti-alias filter cannot be turned on because the
averaging performed the filter would cause incorrect values. This is the case
for on/off channels and channels where the bit values have a particular
meaning, for example error group channels.
Real Time Value (VIM, ADL2, SDL)
For channels that come from a VIM, an ADL2 or an SDL the logging
anti-alias filter also affects the real-time value of the channel. This is the
value that all other parts of the system see, such as the various
calculations.
Note The anti-alias filter is limited to 50 Hz for real time values even if
the channel is logged at a lower rate. For example, a channel logged at
10 Hz will be filtered and updated at 10 Hz in the logging and 50 Hz for
the real time value.
Note Channels that are not logged are updated at 50 Hz.