Publication 1794-6.5.11 - November 1997
Overview of the Frequency Input Module
1
-7
During normal operation, there is a sufficient number of pulses to prevent
the module from entering the 2 second extension mode. Once the user
defined number of pulses is reached within the sampling window, the
frequency is immediately reported.
If the sampling window was extended to 2 seconds while waiting for a
second pulse to occur, a situation which can occur during system startup,
the module will not wait for the number of pulses to be reached. Instead,
as soon as a second pulse occurs, the frequency will be calculated based
on the time between the 2 pulses, and the procedure starts over.
Missing Pulse Multiplier
The last user parameter which is provided to modify the frequency
algorithm is the Missing Pulse Multiplier. In this case, the user can set the
number of Minimum Frequency Sampling Time windows they will allow
to extend the time to capture a second pulse, before reporting a Missing
Pulse Alarm. The intent with this parameter is to allow a tradeoff of the
bandwidth available with the response time to report a missing pulse. This
mechanism is shown in the following figure.
Termination on Number of Pulses
Frequency Reported at
Number of Pulses to Terminate Reached =
T2 - T1
Pulses to Terminate - 1
Minimum Sampling Time
Frequency Input
Pulses
first pulse in window,
T1 time stored
pulses to terminate
number of pulses to
terminate reached
T2, update as each
pulse occurs
Missing Pulse Alarm Would be Reported After 2 Seconds, If No Pulse Occurs